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INFLUENCE OF PACKAGING MATERIALS AND STORAGE CONDITIONS ON THE QUALITY ATTRIBUTES OF
POTATO (Solanum tuberosum L.) TUBERS
KASHIF SARFRAZ ABBASI
95-arid-33
Department of Food Technology
Faculty of Crop and Food Sciences
Pir Mehr Ali Shah
Arid Agriculture University, Rawalpindi
Pakistan
2012
INFLUENCE OF PACKAGING MATERIALS AND STORAGE CONDITIONS ON THE QUALITY ATTRIBUTES OF
POTATO (Solanum tuberosum L.) TUBERS
by
KASHIF SARFRAZ ABBASI (95-arid-33)
A thesis submitted in partial fulfillment of the requirement for the degree of
Ph.D Agriculture
in
Food Technology
Department of Food Technology
Faculty of Crop and Food Sciences
Pir Mehr Ali Shah
Arid Agriculture University, Rawalpindi
Pakistan
2012
ii
CERTIFICATION
I hereby undertake that this research is an original one and no part of this thesis falls
under plagiarism. If found otherwise at any stage, I will be responsible for the consequences.
Student’s Name: Kashif Sarfraz Abbasi Signature. ____________
Registration No: 95-arid-33 Date.
Certified that the contents and form of the thesis entitled “Influence of Packaging
Materials and Storage Conditions on the Quality Attributes of Potato (Solanum
Tuberosum L.) Tubers” submitted by Mr. Kashif Sarfraz Abbasi have been found
satisfactory for the requirement of the degree.
Supervisor ________________________ (Prof. Dr. Tariq Masud)
Member ___________________________ (Dr. Asif Ahmad)
Member __________________________ (Prof. Dr. Muhammad Gulfraz) Chairman _____________________
Dean _____________________ Director Advanced Studies ______________
iii
IN THE NAME OF ALLAH
THE MOST MERCIFUL THE MOST
BENEFICIANT
iv
DEDICATED
TO
THE LOVING MEMORIES
OF
MY DECEASED FATHER
v
ACKNOWLEDGEMENT
I am highly indebted to Almighty Allah (The compassionate the most merciful) who
blessed me enough to carry out this humble effort in the form of present dissertation. I offer
my humblest compliments from the core of my heart to our beloved Prophet Muhammad
(Peace Be Upon Him) the city of knowledge, the highest of mankind who enlightened and
turned the lives of mankind into peace and great moral values.
Triumph begins with the role of parents to culture principles while completes with
the guidance of a teacher. I feel privileged to be associated with my affectionate supervisor
Prof. Dr. Tariq Masud, Chairman, Department of Food Technology who guided me during
the course of this research work with words of wisdom and progressive vision. I am
extremely grateful for his inspiring guidance, generous assistance, and constructive criticism
for the accomplishment of this manuscript.
I am thankful to the worthy members of my supervisory committee; Prof. Dr.
Muhammad Gulfraz and Dr. Asif Ahmad for their scholastic guidance and kind co operation
through out the period of my PhD studies. Sincere thanks are extended to Prof. Dr. M.
Shahbaz Bhatti Ex. Chairman Deptt. of Food Technology for his in time guidance and
technical support. I must pay homage to all the other faculty members of Department of
Food Technology for their continuous support and valuable suggestions during my course of
study.
Its matter of great privilege for me to offer my sincere regards to Prof. Dr.
Muhammad Munir (Ex Vice Chancellor, Arid Agriculture University), Prof. Dr. Tariq
Mahmood (Chairman, Deptt. of Environmental Sciences), Prof. Dr. Muhammad Aslam (Ex.
Chairman, Deptt of Entomology), Dr. Khalid Saifullah Khan (Incharge Central Laboratory),
Mr. Muhammad Nisar (Controller Examinations), Mr. Sohail Mahmood Malik (Dy.
Controller Examinations, Federal Urdu University, Islamabad) Mr. Ayaz Elahi (Dy.
Registrar, Examinations) Dr. Riffat Hayat (Assistant Professor, Soil Science) and Mr.
Mahmood-ul-Hassan (Lecturer, Plant Breeding and Genetics) for their generous cooperation
and time to time assistance.
vi
I found myself fortunate enough to have the company of my Ph.D colleagues Dr.
Ahmad Bilal, Mr. Sartaj Ali, Mr. Talat Mahmood, M. Javed Tarin for their moral support
and judicious advice during my research work. I feel it appropriate to offer my deep sense of
appreciation to my friends Raja Rehan Arif (Marketing Specialist, F&VDP, Lahore), Mr.
Nazar Iqbal (Seed Analyst, FSCD, Islamabad), Dr. Farid Asif Shaheen (SSO, PSF,
Islamabad), Mr Abdus Sattar (NARC, Islamabad) for their valuable inputs during the write
up of this manuscript.
I express my thanks to Higher Education Commission of Pakistan for providing me
the financial assistance through Indigenous Fellowship program to make this project
possible.
Last but not least, I am very grateful to the endless prayer of my mother and all
family members for their patience, support and encouragement throughout my study.
Deepest gratitude I reserve for my wife, daughters and son for their patience and moral
support for my persuasion to higher ideals of life.
(KASHIF SARFRAZ ABBASI)
CONTENTS Page
vii
Certification ii
Dedication iv
Aknowledgement v
List of Tables xiii
ABSTRACT 1
1 INTRODUCTION 3
1.1 ORIGIN AND DISTRIBUTION 3
1.2 PRODUCTION AND VARIETIES 3
1.3 NUTRITIONAL AND MEDICINAL VALUE 5
1.4 POTATO STORAGE PHYSIOLOGY 6
1.5 VALUE ADDITION 8
2 REVIEW OF LITERATURE 11
2.1 SPECIFIC GRAVITY 11
2.2 STARCH 12
2.3 VITAMINS AND MINERALS 15
2.4 POLYPHENOLS 16
2.5 ANTIOXIDANTS 18
2.6 POLYPHENOL OXIDASE 20
2.7 PER OXIDASES 22
2.8 PACKAGING SYSTEMS 23
2.9 POTATO GREENING 30
2.10 POTATO GLYCOALKALOIDS 33
2.11 LOW TEMPERATURE SWEETENING 35
2.12 SUGAR 37
2.13 POTATO SPROUTING 39
2.14 CHIP COATINGS 44
2.15 ACRYLAMIDE 46
3. MATERIALS AND METHODS 49
3.1 PHASE-I 49
viii
3.2 PHASE-II 49
3.2.1 Packaging Trial 50
3.2.2 Light Trial 51
3.2.3 Temperature Trial 51
3.2.4 Sprouting Trial 52
3.3 PHASE-III 53
3.3.1 Potato Chip Coating 54
3.4 PHYSICO-CHEMICAL AND FUNCTIONAL ANALYSIS OF POTATO 55
3.4.1 Physical Analysis 55
3.4.1.1 Size 55
3.4.1.2 Goemetric mean diameter 55
3.4.1.3 Sphericity 55
3.4.1.4 Surface area 55
3.4.1.5 Tuber counts 56
3.4.1.6 Firmness 56
3.4.1.7 Specific gravity 56
3.4.1.8 Total soluble solids 56
3.4.1.9 pH 57
3.4.1.10 Sprouting 57
3.4.1.11 Weight loss 57
3.4.2 Chemical Analysis 57
3.4.2.1 Dry matter 57
3.4.2.2 Starch 58
3.4.2.3 Protein 58
3.4.2.3 Fat 59
3.4.2.4 Sugar 59
3.4.2.5 Glucose 60
3.4.2.6 Fiber 60
3.4.2.7 Ash contents 60
3.4.2.8 Mineral composition 61
3.4.3 Functional Assays 61
ix
3.4.3.1 Ascorbic acid 61
3.4.3.2 Total glycoalkaloids 62
3.4.3.3 Chlorophyll 63
3.4.3.4 Total phenolic contents 63
3.4.3.5 Radical scavenging activity 64
3.4.3.6 Enzyme estimation 65
3.4.3.6.1Extraction and protein estimation 65
3.4.3.6.2 Polyphenol oxidase (PPO) assay 65
3.4.3.6.3 Per oxidase (POD) assay 66
3.4.4 Potato Chips Evaluation 66
3.5 STATISTICAL ANALYSIS 67
4. RESULTS AND DISCUSSION 68
4.1 PHYSICO-CHEMICAL, FUNCTIONAL AND PROCESSING
ATTRIBUTES OF POTATO VARIETIES 68
4.1.1 Physical Attributes of Potato Varieties 68
4.1.2 Proximate Analysis of Potato varieties 71
4.1.3 Functional Attributes of Potato Varieties 76
4.1.4 Potato Chips Evaluation 78
4.2 EFFECT OF DIFFERENT PACKAGING MATERIALS ON THE
QUALITY ATTRIBUTES OF POTATO 81
4.2.1 Effect on Weight Loss 81
4.2.2 Effect on Total Soluble Solids 85
4.2.3 Effect on pH 87
4.2.4 Effect on Specific Gravity 90
4.2.5 Effect on Glucose 93
4.2.6 Effect on Total Sugars 96
4.2.7 Effect on Starch 98
4.2.8 Effect on Ascorbic Acid 101
4.2.9 Effect on Total Glycoalkaloids 103
4.2.10 Effect on Total Phenolic Contents 106
x
4.2.11 Effect on Radical Scavenging Activity 108
4.2.12 Effect on Polyphenol Oxidase Activity 112
4.2.13 Effect on Peroxidase Activity 115
4.2.14 Effect on Chip Moisture Contents 118
4.2.15 Effect on Chip Fat Absorption 121
4.2.16 Effect on Chip Color 123
4.2.17 Effect on Chip Crispiness 126
4.2.18 Effect on Chip Flavor 128
4.3 EFFECT OF DIFFERENT LIGHT SOURCES ON THE
QUALITY ATTRIBUTES OF POTATO 130
4.3.1 Effect on Weight Loss 130
4.3.2 Effect on Total Soluble Solids 133
4.3.3 Effect on Color 135
4.3.4 Effect on Glucose 137
4.3.5 Effect on Total Sugar 139
4.3.6 Effect on Starch 141
4.3.7 Effect on Ascorbic Acid 143
4.3.8 Effect on Chlorophyll 146
4.3.9 Effect on Total Glycoalkaloids 149
4.3.10 Effect on Total Phenolic Contents 151
4.3.11 Effect on Radical Scavenging Activity 154
4.3.12 Effect on Chips Moisture Contents 156
4.3.13 Effect on Chip Fat Absorption 159
4.3.14 Effect on Chip Color 159
4.3.15 Effect on Chip Crispiness 163
4.3.16 Effect on Chip Flavor 165
4.4 EFFECT OF DIFFERENT TEMPERATURE STORAGE ON THE
QUALITY ATTRIBUTES OF POTATO 167
4.4.1 Effect on weight Loss 167
4.4.2 Effect on Total Soluble Solids 170
4.4.3 Effect on Glucose 172
xi
4.4.4 Effect on Total Sugars 175
4.4.5 Effect on Starch 177
4.4.6 Effect on Ascorbic Acid 181
4.4.7 Effect on Chlorophyll 183
4.4.8 Effect on Total Glycoalkaloids 186
4.4.9 Effect on Total Phenolic Contents 188
4.4.10 Effect on Radical Scavenging Activity 191
4.4.11 Effect on Polyphenol Oxidase Activity 194
4.4.12 Effect on Peroxidase Activity 196
4.4.13 Effect on Chip Moisture Content 199
4.4.14 Effect on Chip Fat Absorption 202
4.4.15 Effect of Chip Color 204
4.4.16 Effect on Chip Crispiness 207
4.4.17 Effect on Chip Flavor 209
4.5 EFFECT OF DIFFERENT ANTI SPROUTING AGENTS ON THE
QUALITY ATTRIBUTES OF POTATO 212
4.5.1 Effect on Weight Loss 212
4.5.2 Effect on Total Soluble Solids 215
4.5.3 Effect on Sprouting 218
4.5.4 Effect on Specific Gravity 220
4.5.5 Effect on Glucose 221
4.5.6 Effect on Total Sugars 225
4.5.7 Effect on Starch 227
4.5.8 Effect on Total Glycoalkaloids 230
4.5.9 Effect on Total Phenolic Contents 233
4.5.10 Effect on Radical Scavenging Activity 235
4.5.11 Effect on Polyphenol Oxidase Activity 238
4.5.12 Effect on Peroxidase Activity 241
4.5.13 Effect on Chip Moisture Content 244
4.5.14 Effect on Chip Fat Absorption 246
4.5.15 Effect on Chip Color 249
xii
4.5.16 Effect on Chip Crispiness 251
4.5.17 Effect on Chip Flavor 253
4.6 EFFECT OF INTEGRATED TREATMENTS ON THE QUALITY
ATTRIBUTES OF POTATO 256
4.6.1 Effect on Weight Loss 256
4.6.2 Effect on Total Soluble Solids 258
4.6.3 Effect on Sprouting 261
4.6.4 Effect on Glucose 263
4.6.5 Effect on Total Sugar 265
4.6.6 Effect on starch 267
4.6.7 Effect on Ascorbic Acid 269
4.6.8 Effect on Chlorophyll 272
4.6.9 Effect on Total Glycoalkaloids 274
4.6.10 Effect on Total Phenolic Contents 276
4.6.11 Effect on Radical Scavenging Activity 279
4.6.12 Effect on Polyphenol Oxidase Activity 282
4.6.13 Effect on PerOxidase activity 284
4.6.14 Effect on Chip Moisture Contents 286
4.6.15 Effect on Chip Fat Absorption 289
4.6.16 Effect on Chip Color 291
4.6.17 Effect on Chip Crispiness 293
4.6.18 Effect on Chip Flavor 295
GENERAL DISCUSSION 298
CONCLUSIVE SUMMARY 305
RECOMMENDATIONS 311
LITERATURE CITED 312
LIST OF TABLES
xiii
Table No. Page 1a. Physical attributes of potato varieties 69
1b. Correlation between physical attributes 70
2a. Proximate analysis of potato varieties 72
2b. Correlation between proximate components 73
3. Mineral composition of potato varieties 74
4a. Functional attributes of potato varieties 77
4b. Correlation between functional attributes 77
5a. Evaluation of potato chips 79
5b. Correlation between potato chips attributes 80
xiv
LIST OF FIGURES
Figure No
Page
Fig. 1 Weight loss in potato under different packagings showing minimum
loss in polypropylene and LDPE during storage
83
Fig. 2 Total soluble solids in potato under different packagings showing highest
increase in control during storage
86
Fig. 3 pH in potato under different packagings showing maximum retention in
polypropylene and LDPE during storage
88
Fig. 4 Specific gravity in potato under different packagings showing maximum
value in LDPE during storage
91
Fig. 5 Glucose in potato under different packagings showing lowest contents in
polypropylene during storage
95
Fig. 6 Total sugar in potato under different packagings showing lowest contents in
polypropylene and LDPE during storage
97
Fig. 7 Starch in potato under different packagings depicting maximum decline in
control during storage
100
Fig. 8 Ascorbic acid in potato under different packagings showing highest
retention in polypropyleneduring storage
102
Fig. 9 Total glycoalkaloids in potato under different packagings showing highest
increase in control during storage
105
Fig. 10 Total phenolic contents in potato under different packagings showing
maximum retention in polypropylene during storage
107
Fig. 11 Radical scavenging activity in potato under different packagings showing
highest activity in polypropylene during storage
110
Fig. 12 Polyphenol oxidase in potato under different packagings showing lowest
enzymatic activity in LDPE during storage
113
Fig. 13 Per oxidase in potato under different packagings maintaining lowest
enzymatic activity in polypropylene and LDPE during storage
117
Fig. 14 Chip moisture content in potato under different packagings showing
highest increase in control during storage
120
xv
Fig. 15 Chip fat absorption in potato under different packagings showing maximum
value in control during storage
122
Fig. 16 Chip color in potato under different packagings showing highest
value in polypropylene during storage
124
Fig. 17 Chip crispiness in potato under different packagings showing highest
value in polypropylene and LDPE during storage
127
Fig. 18 Chip flavor in potato under different packagings showing highest
value in polypropylene during storage
129
Fig. 19 Weight loss in potato under different light sources showing minimum loss
in dark followed by mercury during storage
132
Fig. 20 Total soluble solids in potato under different light sources showing lowest
increase in dark and green light during storage
134
Fig. 21 Color in potato under different light sources showing highest scores in dark
during storage
136
Fig. 22 Glucose in potato under different light sources showing highest increase in
florescent light during storage
138
Fig. 23 Total Sugar in potato under different light sources showing highest
increase in florescent light during storage
140
Fig. 24 Starch in potato under different light sources showing highest decline in
florescent and red lights during storage
142
Fig. 25 Ascorbic Acid in potato under different light sources showing highest
retention indark followed by green light during storage
145
Fig. 26 Chlorophyll in potato under different light sources showing maximum
increase in florescent and blue lights during storage
147
Fig. 27 Total glycoalkaloids in potato under different light sources showing
highest increase in florescent light during storage
150
Fig. 28 Total phenolic contents in potato under different light sources showing
maximum retention in green light during storage
152
Fig. 29 Radical scavenging activity in potato under different light sources showing
highest activityin dark during storage
155
xvi
Fig. 30 Chip moisture contents in potato under different light sources showing lowe
value in dark during storage
157
Fig. 31 Chip fat absorption in potato under different light sources showing lowest
value in dark during storage
160
Fig. 32 Chip color in potato under different light sources showing highest value in
dark and green light during storage
162
Fig. 33 Chip crispiness in potato under different light sources showing highest scor
in dark and green light during storage
164
Fig. 34 Chip flavor in potato under different light sources showing highest scores
in dark and green light during storage
166
Fig. 35 Chip flavor in potato under different light sources showing highest scores
in dark and green light during storage
168
Fig. 36 Total soluble solids in potato under comparative temperature storage
showing maximum increase at 5oC
171
Fig. 37 Glucose in potato under comparative temperature storage showing maximu
contents at 5oC
174
Fig. 38 Total sugar in potato under comparative temperature storage showing
maximum contents at 5oC
176
Fig. 39 Starch in potato under comparative temperature storage maintaining
maximum contents at 15oC
179
Fig. 40 Ascorbic acid in potato under comparative temperature storage
maintaining maximum retention at 5oC
182
Fig. 41 Chlorophyll in potato under comparative temperature storage maintaining
maximum contents at 25oC
185
Fig. 42 Total Glycoalkaloids in potato under comparative temperature storage
showing lowest contents at 5oC
187
Fig. 43 Total phenolic contents in potato under comparative temperature storage
showing maximum retention at 5oC
189
Fig. 44 Radical scavenging activity in potato under comparative temperature
storage showing highest activity at 5oC
192
Fig. 45 Polyphenol oxidase in potato under comparative temperature storage 195
xvii
showing lowest enzymatic activity at 5oC
Fig. 46 Per oxidase in potato under comparative temperature storage showing lowe
enzymatic activity at 5oC
198
Fig. 47 Chip moisture content in potato under comparative temperature storage
showing highest contents at 25oC
200
Fig. 48 Chip fat absorption in potato under comparative temperature storage
showing highest value at 25oC
203
Fig. 49 Chip color in potato under comparative temperature storage showing highes
value at 15oC
205
Fig. 50 Chip crispiness in potato under comparative temperature storage showing
highest value at 15oC
208
Fig. 51 Chip Flavor in potato under comparative temperature storage showing high
value at 15oC
210
Fig. 52 Weight loss in response to different sprout inhibitors showing minimum
loss in CIPC during potato storage
213
Fig. 53 Total soluble solids in response to different sprout inhibitors showing
maximum increase in control during potato storage
217
Fig. 54 Sprouting in response to different sprout inhibitors showing maximum
percentage in control during potato storage
219
Fig. 55 Specific gravity in response to different sprout inhibitors showing lowest
value in control during potato storage
222
Fig. 56 Glucose in response to different sprout inhibitors showing highest
increase in control during potato storage
224
Fig. 57 Total sugar in response to different sprout inhibitors showing highest
increase in control during potato storage
226
Fig. 58 Starch in response to different sprout inhibitors showing maximum
contents in CIPC and clove during potato storage
229
Fig. 59 Total glycoalkaloids in response to different sprout inhibitors showing
lowest increase in CIPC and clove during potato storage
231
Fig. 60 Total phenolic contents in response to different sprout inhibitors showing
maximum retention in CIPC and clove during potato storage
234
xviii
Fig. 61 Radical scavenging activity in response to different sprout inhibitors
showing highest activity in CIPC and clove during potato storage
237
Fig. 62 Polyphenol oxidase in response to different sprout inhibitors showing
lowest enzymatic activity in CIPC and clove during potato storage
239
Fig. 63 Per oxidase in response to different sprout inhibitors showing lowest
enzymatic activity in CIPC and clove during potato storage
242
Fig. 64 Chip moisture contents in response to different sprout inhibitors showing
highest contents in control during potato storage
245
Fig. 65 Chip fat absorption in response to different sprout inhibitors showing
highest contents in control during potato storage
248
Fig. 66 Chip color in response to different sprout inhibitors showing highest
scores in CIPC and clove during potato storage
250
Fig. 67 Chip crispiness in response to different sprout inhibitors showing highest
scores in CIPC and clove during potato storage
252
Fig. 68 Chip flavor in response to different sprout inhibitors showing highest
scores in CIPC and clove during potato storage
255
Fig. 69 Weight loss in response to integrated treatment showing minimum loss as
compare to control during storage
257
Fig. 70 Total soluble solids in response to integrated treatment showing lower
contents as compare to control during storage
260
Fig. 71 Sprouting in response to integrated treatment showing lower percentage
as compare to control during storage
262
Fig. 72 Glucose in response to integrated treatment showing lower contents as
compare to control during storage
264
Fig. 73 Total sugar in response to integrated treatment showing lower contents as
compare to control during storage
266
Fig. 74 Starch in response to integrated treatment maintaining higher contents as
compare to control during storage
268
Fig. 75 Ascorbic acid in response to integrated treatment maintaining higher 271
xix
contents as compare to control during storage
Fig. 76 Chlorophyll in response to integrated treatment maintaining lower
contents as compare to control during storage
273
Fig. 77 Total Glycoalkaloids in response to integrated treatment maintaining
lower contents as compare to control during storage
275
Fig. 78 Total phenolic contents in response to integrated treatment maintaining
higher contents as compare to control during storage
278
Fig. 79 Radical scavenging activity in response to integrated treatment
maintaining higher activity as compare to control during storage
280
Fig. 80 Polyphenol oxidase in response to integrated treatment showing lower
enzymatic activity as compare to control during storage
283
Fig. 81 Per oxidase in response to integrated treatment showing lower enzymatic
activity as compare to control during storage
285
Fig. 82 Higher Chip moisture content in potato chips due to aloe vera (A.V)
coatings as compare to control
287
Fig. 83 Higher Chip fat absorption in potato chips due to aloe vera (A.V)
coatings as compare to control.
290
Fig. 84 Comparision of Chip color in response to aloe vera (A.V) coatings on
potato chips
292
Fig. 85 Comparision of Chip crispiness in response to aloe vera (A.V) coatings
on potato chips
294
Fig. 86 Comparision of Chip flavor in response to aloe vera (A.V) coatings on
potato chips
296
ABSTRACT
Agro ecological diversity and favorable environment have enabled Pakistan to
harvest bulk of potato crop however facing problems of poor post harvest management
practices and unavailability of superior raw material for the potato processing industry.
A comprehensive study was planned to identify best packaging material and
appropriate storage conditions for the premium potato variety. The present study has
been divided in to three different phase to address specific objectives. The first phase
of study encompasses physico-chemical, functional and processing attributes in
prominent potato varieties. The selected variety was subjected to different post harvest
storage conditions along with their processing parameters analysis in second phase of
the study. The last phase of study evaluated the storage stability of premium variety
under best results identified in the second phase. In the first phase of study, physical
attributes (tuber size, geometric mean diameter, sphericity, surface area, firmness,
specific gravity, total soluble solids, pH, sprouting %, tuber color) Chemical attributes
(dry matter, starch, protein, fat, sugar, fibre, ash and predominant minerals) functional
attributes (ascorbic acids, glycoalkaloids, total phenolic contents, radical scavenging
activity) and processing performance (chip moisture contents, fat absorption, color and
sensorial attributes) were evaluated in ten commercial varieties i.e. Agria, Atlantic,
Cardinal, Chipsona, Courage, Desi, Desiree, Hermes, Lady Rosetta, and Satellite. In
general Lady Rosetta followed by Hermes was the most appreciable variety regarding
their physical attributes. Lady Rosetta followed by Atlantic attained maximum dry
matter and starch contents. Least sugar contents were recorded in Agria and maximum
fat and protein contents were quantified in Desiree. In general; functional attributes
were found maximum in Desi followed by Desiree. A promising correlation was
estimated between most of these parameters with distinctive correlation (R=0.903)
identified between total phenolic contents and radical scavenging activity. Post
processing parameters like moisture contents, fat absorption, and sensory evaluation in
Lady Rosetta showed its preference over all other varieties followed by Hermes. In the
second phase variety” Lady Rosetta” was evaluated under different storage conditions
1
2
(packaging, light, temperature, and anti sprouting agents) on the basis of transition in
their quality attributes (reported in 1st phase) and enzymatic (polyphenol oxidase,
peroxidase) activities. Potatoes were stored under different packaging materials (jute,
nylon, polypropylene, cotton, low density polyethylene, medium density polyethylene,
high density polyethylene) at ambient temperature (25±2oC). Results revealed that
polypropylene packaging and low density polyethylene packaging were found best and
maintained tubers quality attributes up to 63 days, while other packaging materials
were also found effective as compare to control. Thirty days storage of tubers under
different illuminations (blue, fluorescent, green, mercury, red, dark) at ambient
temperature (25 ±2oC) was carried out. Potato tubers kept under dark presented
minimum loss of quality parameters however green and mercury lights posed best
storage performance over all other illuminations during one month. Tubers were found
highly susceptible to fluorescent light with poor processing attributes were recorded in
red and blue light exposures. Results under comparative temperature regimes (5, 15
and 25oC) showed maximum storage stability up to 126 days under 5oC, however
associated with low enzyme activity, elevated sugars contents in tubers and poor
processing performances in fried chips. Exposing tubers to different anti sprouting
agents (hot water treatment, spearmint oil, clove oil, CIPC) showed that CIPC and
Clove oils applications were found significant in preventing tuber sprouting at the end
of 80 days storage. In general, both retained superior tuber characters with remarkable
processing characters during the storage period. Tuber dormancy was ensured under
both treatments till the end at ambient temperature (25 ± 2oC) storage. In the last phase
integrated post harvest management of potato variety “Lady Rosetta” on the basis of
best results identified in second phase ensured tuber dormancy and prolonged storage
life up to 180 days with appreciable retention of tuber quality attributes and superior
processing performance as compare to 100% sprouting observed in control on the 80th
day of storage. Coating of potato chips with 20% aloe vera gel presented best results
with reduced fat uptake along with appreciable sensorial scores.
3
Chapter 1
INTRODUCTION
Potato (Solanum tuberosum) belongs to solanaceae family and is a
perennial plant, which is herbaceous in nature. The plant however is grown in
Pakistan annually and its propagation is carried out through tubers, which are thick
puffy part of the rhizome found underground and covered by modified eyes and
buds. The climatic requirements of potato are cool and moist but frost brings
mechanical injury, which is detrimental for the crop. The stem tuber is the edible
part of the crop which serves as an energy reservoir and commonly employed for
vegetative propagation purpose. Botanically potato tuber is an extension of stolon
arising from the buds at the base of stem (Beukema and Vander-Zaag, 1990).
1.1 ORIGIN AND DISTRIBUTION
Potato is native to several countries of Latin American continent like Peru,
Chile, Bolivia, Argentina, Colombia etc. It is believed that the cultivated potato
was derived from the feral species found in South America, particularly in the
Andes of Peru and Bolivia. The crop is introduced in the European continent
through Spain and then into England. The wide spread of this crop through out the
world is witnessed during the start of 17th century into different British colonies
like Ireland, Scotland, United states and Indo-Pak subcontinent (Hawkes, 1978).
1.2 PRODUCTION AND VARIETIES
Potato is number one non-grain food crop in the world and one third of the
total production is being harvested in densely populated developing countries, like
3
4
China and India, and thus alleviates the food crisis in third world countries (PIC,
2008). It is ranked top most important crop in South American continent, second
most important crop in Europe and fourth on the Globe after wheat, rice and maize
(Messer, 2000). The overall estimated yield of potato in the world is about 320.67
million tons and China being the major contributor produces 72 million tons
followed by Russian Federation and India with yield of 35.7 and 26.2 million tons
respectively. The demand for potato in the international market is one the rise and
all the major exporting countries are trying to increase the yield and as a reciprocal
increase their share in world market (FAO, 2007).
Potato is the most imperative and widely cultivated vegetable crop in
Pakistan with an estimated 2.5 million tons production from an area of 150
thousand hectare. Punjab province produces the lion’s share of potato crop
contributing 90% and the rest of the three provinces produce 10 % of the total
potato produce of Pakistan in an order of Khyber Pakhtun Khwa being a leading
producer followed by Balochistan and Sindh (GOP, 2009). The overall availability
in world market is however below par and Pakistan contributes only around 1% in
world production. Despite significant area under cultivation and multiple growing
seasons the annual export remained only 50,000 tons contributing 0.5% of the
world export. The main potato export markets are Sri Lanka and Afghanistan
(PHDEB, 2008)
Potato carries broad biodiversity, with more than 4000 known varieties
most of which belong to the species Solanum tuberosum consumed in 150
countries of the world (Burlingame et al., 2009). Few of the most recognized
varieties of potato in Pakistan are red skinned (Desiree, Courage, Cardinal,
Kuroda, Lady Rosetta, Raja, etc.) and white skinned (Agria, Hermes, Chipsona,
5
Satellite, Sante, Diamont, etc.), which are produced on large scale across the
country and consumed for processing and table use (PHDEB, 2008).
1.3 NUTRITIONAL AND MEDICINAL VALUE
The world wide consumption of potatoes is ascribed to its lusciousness and
high nutritive value (Rytel et al., 2005). It produces more dry matter per hectare
than the major cereal crops like wheat, rice etc (Gravoueille, 1999) thus considered
as an important staple crop in most parts of the world. Potatoes are a rich source of
carbohydrate with starch being the key ingredient or the main form, which serves
as an inexpensive source of energy (Lachman et al., 2001). In addition it is also
considered as good source of high-quality protein such as lysine (Friedman, 2004).
One hundred grams of potato provides 90 kilocalories energy containing vital
constituents like water 75.0 grams, carbohydrates 19.0 grams , fat 0.1grams,
protein 2.0 grams, Thiamin (Vit.B1) 0.08 mg, Riboflavin (Vit.B2) 0.03 mg, Niacin
(Vit.B3) 1.1 mg, Vitamin B6 0.25 mg, Vitamin C 20.0 mg, Calcium 12.0 mg, Iron
1.8 mg, Magnesium 23.0 mg, Phosphorus 57.0 mg and Sodium 6.0 mg. (Raban et
al., 1994).
Four of the six main vitamins required in our daily diet are present in
potatoes, which speak highly of the nutritious importance of the crop. The vitamins
found in potatoes are ascorbic acid, thiamin, riboflavin and niacin. Among others
ascorbic acid is the main vitamin present as dietary antioxidant, which is
vulnerable against heat and light thus considered as major index of quality
deterioration duration storage (Burlingame et al., 2009). In addition potatoes are
the second most imperative source of vitamin B6 for the elderly who are
particularly at risk of chronic diseases. Vitamin B6 influences hormonal synthesis,
erythrocyte production, immune modulation and central nervous system functions.
6
In addition is also important against treatment of various chronic diseases such as
sickle cell anemia, asthma, and cancer (Kolasa, 1993). Potato is low cholesterol,
high potassium food with significant antioxidants potential thus capable of
protecting human beings against cardiovascular diseases and cancer (Lachman et
al., 2000). Polyphenol in addition are the most common dietary antioxidant
(Lachmann et al., 2008) being efficient as reducing agents, metal chelators and
reactive oxygen species quenchers in biological system.
1.4 POTATO STORAGE PHYSIOLOGY
Potato tuber undergoes physiological dormancy period during the
postharvest storage. The length of the dormancy period is dependent on the
varietal genetic profile, environmental factors and storage conditions. Commercial
potato cultivars grown for the processing industry have shorter dormancy periods
and associated with different storage disorders like sweetening, greening, toxicity
etc; therefore it is obligatory to employ suitable storage conditions to ensure their
continuous supply (Suttle, 2007). It is literally impossible to prevent potato tubers
from light exposure during the marketing chain and commercial processing. The
response however, presents remarkable changes in the physiology of the potato
tuber and deteriorates its quality by either inducing sweetness or sprouting or any
other morphological change. Such undesirable changes also include tuber
greening due to excessive chlorophyll accumulation and formation of toxic
steroidal glycoalkaloids.
Glycoalkaloids are present as alpha-solanine and alpha-chaconine in
marginal tuber layers however with the increased amassing of the compounds,
significant economic losses coupled with food safety hazards are observed.
Presently high glycoalkaloids (GA) intake considered as grave food safety concern
7
and with the increasing demand for fresh and processed potatoes the threat has
increased manifold (Percival, 1999). Excessive glycoalkaloids accumulation leaves
bitter taste if the concentration goes past a specific level with upper safe intake
limit for human is 20 mg/100g f.w (Nema et al., 2008). Excessive glycoalkaloids
intake result in diarrhea, vomiting, fever, rapid pulse, colic pain, low blood
pressure, gastroenteritis, and neurological disorders (Slanina, 1990). Although
abundant chlorophyll formation in potatoes is not serious threat for human body
but green potatoes appear to be highly unattractive in comparison to normal red
skinned or white skinned potatoes. The unappealing green color of the potatoes
reduce their market value and according to a research carried out by British potato
council, £ 6 million loss has been borne by the grower due to its green
pigmentation (Anon, 1998).
The efficient sprout control is necessary to maintain effective tuber quality
and minimal storage losses. Sprouting can increase tuber weight loss primarily due
to rapid evapotranspiration through the lenticels and leads to elevated reducing
sugar level (Hartmans et al. 1995). In addition, sprouted tubers are ascribed to the
elevated levels of toxic glycoalkaloids (Friedman, 2006). Sprouting in potato can be
controlled by using different sprout inhibitors like CIPC (Fauconnier et al., 2002),
Sprout suppressants like essential oils (Kleinkopf et al., 2003), irradiations (Rezaee
et al., 2011) pressure application (Saraiva et al., 2011 ) and hot water treatments
(Kyriacou et al., 2008).
Potato is semi perishable crop however placed under low temperature
storage to prevent them from sprouting and to ensure their regular supply
whenever required. Low temperature potato storage is however associated with
8
low temperature sweetening and is specifically undesirable in processing potato
varieties (Kyriacou et al., 2009). The phenomenon is primarily associated with the
potato storage under low temperature and as a result of which the insoluble starch
is enzymatically hydrolyzed into soluble glucose, fructose and sucrose
(Sowokinos, 1990). Tuber sweetening deteriorates tuber commercial quality and
causes the fried products to turn brown and bitter in taste due to subsequent
acrylamide formation. Acrylamides are toxic compounds produced in the fried
potato products as a by-product of the maillard reaction in the presence of major
precursors like reducing sugar (glucose) and the amino acid (asparagines)
(Mottram et al., 2002).
1.5 VALUE ADDITION
Potato value addtition includes different commercial preparations like
potato chips, mashed potatoes, steamed potato, potato patties, whole baked
potatoes, potato flakes and dehydrated potato granules. Commercial production of
alcoholic beverage and adhesive in manufacturing industries are also some of the
other uses of this important crop especially in developed countries. Potato is one of
the very few vegetables with lot of serving variations which can both be served hot
as potato chips and cold as potato salad without losing its peculiar taste. Another
important dish is mashed potatoes in which the potatoes are boiled, peeled and
served after mashing them with milk, yogurt or butter (Christine, 1996). However
the most important one being the potato chips which gained terrific economic
value in processed food industry. The most important among snack products is
discovered back in 1853 by George Crum an American Chef, and gained
tremendous popularity in processed food industry. Currently, Potato chips
contributes major share in the snack food market of the world and generated total
9
revenues of US$16.4 billion in 2005 (www.Potatopro.com) and the consumption of
this important snack exceeds 1.2 billion pounds per year in United States (Clark
2003).
Reduction of post harvest losses is an area of grave concern and several
loss reduction techniques have been developed over time, which not only limit the
post harvest losses but also improve the quality of horticultural commodities. Low
and high temperature, modified atmosphere, controlled atmosphere, hypobaric
storage, irradiation etc. are few of the physical methods to achieve the objective of
reduction of post harvest losses and final quality maintenance. The chemical
methods used for this purpose include waxes, edible coatings, fungicides, ethylene
absorbents, senescence retardants etc.
Several varieties of potato have been developed and released to the farmers,
even though these varieties exhibit appreciable tuber characteristics, the
comprehensive data regarding their proximate composition, mineral contents,
functional potential and processing performance under local ecological condition
(weather, soil, irrigation) were mainly unknown. In addition appropriate
postharvest management of this very important crop is desirable to fetch premium
share in the International market. Few of the appropriate measures include on farm
low cost storage, hydrocooling, modified atmosphere packaging and
waxing/coating. One of the major pre requisites before marketing of the produce is
sorting, grading followed by quality oriented packaging according to international
standards. The horticultural commodities have a short shelf life and the improved
post harvest management techniques involving proper sorting, grading, packaging,
labeling and transportation through the supply chain not only increases the shelf
life but also brings material gains to the farmers. In this regard approprate storage
10
conditions (Temperature, Light) along with the suitable sprout inhibitor are needed
to be identified in order to conserve the commericial value and to enhance the
storage stability of this important crop. A comprehensive study is therefore
designed with following objectives addressed in different section of this
manuscript:
1. To analyze different Physico-chemical, functional and processing attributes
of some important potato varieties grown in Pakistan.
2. To identify the suitable packaging material for the premium variety
3. To establish appropriate storage temperature for the selected potato variety
4. To evaluate the best light source for the selected variety
5. To investigate the best sprout control under storage period.
6. To establish integrated management system to asses the storage life of
selected potato variety.
11
Chapter 2
REVIEW OF LITERATURE
Potato is gradually becoming one of the most important crops both for the
farmers and the consumers in Pakistan. The production volume places it at number
four amongst major crops of Pakistan and its high nutritive value and yield gives it
an additional value. At the time of independence the area under potato was about
three thousand hectares and the yield obtained from the cultivated area was about
thirty thousand tons (Malik, 1995). The scenario has gradually changed over the
years and in the last few decades it has become Pakistan’s fastest growing staple
crop. Presently 2.5 million ton production of potato can easily address the issue of
food security for the expanding population of Pakistan (GOP, 2009).
Potato being important cash crops with substantial exportable potential can
improve farm incomes and foreign exchange earnings for the country. Major
varieties that have been cultivated in Pakistan for table and processing purpose are
of Dutch origin and physiochemical evaluation of these varieties under indigenous
environmental conditions is very important to identify their potential in growing
market for table and processed consumption (PHDEB, 2008).These attributes
defines the economic importance of these varieties and establish their ultimate use.
The present study investigated transition in different quality attributes of potato in
response to different packaging systems and storage conditions.
2.1 SPECIFIC GRAVITY
Specific gravity is one of the most important tools for the quality
evaluation of potato variety and is largely associated with the presence of its dry
matter or total solid contents. The correlation between specific gravity and
11
12
processing quality of potato is eminent (Komiyama et al., 2007), and the potato
processing industry for the production of chips and French fries mostly depends
on the specific gravity for the acceptable quality of processed products (Haynes,
2001). Gould, (1999) reported that for an every 0.005 increase in specific gravity
an approximate increase of one percent in the chip yield is achieved, thus enables
the processor to find and select tuber of high solid content with minimum effort
and time.
Specific gravity varies between different potato varieties as some are
intrinsically of high total solid contents. Under comparable growing conditions
certain varieties are consistently high in dry matter contents such disparity has
also been reported by previous researchers (Lefort et al., 2003). Different methods
has been developed to determine the specific gravity in potato varieties like,
hydrometer (Snack Food Association, 1991) brine solution (Lusas and Rooney,
2001) weight of potatoes in air and water (Kumar et al., 2005) etc. Specific
gravity affects the oil uptake in the processed potato products like Chips, French
fries etc (Sinha et al., 1992). Potato varieties with a high specific gravity have
been revealed to produce a high yield of chips with low oil uptake (Kita, 2002). A
positive relationship between specific gravity and oil uptake in thin sliced sweet
potato crisps has also been reported by Hagenimana et al. (1998).
2.2 STARCH
Starch is the most important caloric nutrient and contributing 70-80% of the
dry matter of the potato which accounts to its close correlation with the specific
gravity and dry matter contents. The two main components of starch i.e Amylose
and Amylopectin are present in the ratio of 1:3 (Salunkhe and Desai, 1984). The
sugar produced in the leaves of potato plants are translocated to the growing tissues
13
where they are converted into starch which is primarily mediated through the
polymerization activities of starch synthetase enzyme (Fernie et al., 2002). The
energy requirement of dormant potato tuber during post harvest storage and
sprouting initiation is largely dependent on this polymerized starch. Biemelt et al.,
(2000) reported that sprouting in stored potato is largely dependent on the
hydrolysis of starch content, which offer substantial energy for the growth and
development of sprouts.
Potato processing and other related industries require examination
concerning starch quality and dry matter (DM) contents of potato tubers. Haase,
(2003) reported the Coefficients values (R2) for dry matter and starch
concentration respectively were 0.92 and 0.83 (starch concentration involving 14
and 24%), and 0.94 and 0.88 (starch concentration ≥14%). In addition both
constituents were checked by near infrared spectroscopy. (R2 justification set was
0.98 and 0.97 for dry material and starch concentration, correspondingly). He
concluded the effectiveness of near infrared technique with a reduced amount of
deviation than the under-water weighting techniques.
Liu et al. (2003) determined physico-chemical properties of starch isolated
from three potato cultivars (Snowden, Shepody and Superior) during development.
Various analytical techniques like Differential scanning calorimetry for
retrogradation and gelatinization, Structure of crystalline starch by X-ray
diffraction method and Rapid viscosity analysis for starch glue viscosity and
pasting temperature were carried out. The content of starch of potato tubers
showed a great variation during its growth with maximum around 2–3 months.
Shepody and Snowden had high starch content as compared to Superior; X-ray
14
diffraction model of starch granule remained unchanged during potato
development time. Starch of Shepody cultivar showed peak absolute viscosity,
maximum temperature and smaller value of enthalpy of gelatinization and
retrogradation. Minimum growth time of potatoes caused lower swelling, elevated
amylose concentration and top gelatinization temperature, pasting temperature and
finishing viscosity of starches.
Casanas et al. (2009) studied eight different cultivars and three
species/subspecies like Solanum x chaucha, Solanum tuberosum spp. tuberosum
and spp. andigena were harvested in Tenirife and evaluated for their proximate
composition. The study revealed lot of variations in all cultivars and
species/subspecies with respect to its chemical analysis. Mean values for moisture
contents showed a lot of variation among the three species/subspecies under study.
Potatoes belonging to spp. tuberosum revealed high level of moisture content as
compared to S. x chaucha, and higher level in latter than the spp. Andigena. Local
potatoes were smaller in size with lower moisture contents and higher nutritional
level. Study concluded negative correlation between starch and moisture contents.
LDA analysis showed significant differences between local and newly imported
potato varieties.
The textural attributes in tubers like consistency, mealiness, sloughing etc
are largely associated to its starch properties and subsequently changes during the
processing. Kita, (2002) identified the relationship between chip texture and
starch, non-starch polysaccharides. Amongst five tested varieties, Saturn’’ and
‘‘Panda’’ varieties exhibited best texture in crisps owing to its palpable starch
and non starch contents.
15
2.3 VITAMINS AND MINERALS
In addition to significant carbohydrates and quality proteins contents
(Friedman, 2004), potato provides a substantial contribution to the daily supply of
vitamins and minerals. They are significant source of minerals like potassium,
phosphorous, calcium etc. (Andre et al., 2007) and their value in the human diet is
highly appreciated as a prime source of ascorbic acid (Dale et al., 2003). Vitamin
C is the predominant vitamin present in potato and of significant functional
importance (Davey et al., 2000). It acts as a natural antioxidant by donating
electrons and scavenging free radicals thus preventing cellular damage inside the
biological system (Padayatty et al., 2003). It aids in collagen production, facilitate
iron absorption, promote wounds healing, and maintain healthy gums eventually
improve the overall immune system (Goggs et al., 2005). During post harvest
storage of fruits and vegetables ascorbic acid known to be effected by factors like
light, heat, oxygen, prolonged storage, mechanical damage, chilling injury, relative
humidity, variety, soil type, physiological stages etc. (Lee and Kader, 2000).
Ascorbic acid is known to be powerful natural antioxidant being capable of
deactivating reactive oxygen species by conjugation with other antioxidant as in
ascorbate-glutathione cycle (Jimenez et al., 1996). It also prevents enzymatic
browning in fruits and vegetables by the reduction of quinones back into phenolic
substrates (Robert et al., 2003) however oxidized itself into dehydro-ascorbic acid
(Padayatty et al., 2003). It have also been used in different food preparations for
the prevention of enzymatic browning, color retention and effective post harvest
application for storage life extension.
Potato being low fat food is also being considered as an imperative source
of vitamins A and B (Lachman et al., 2000). They are the second most important
16
contributor of vitamin B6, which involved in amino acid, nucleic acid, glycogen,
and lipid metabolism and thus regulates immune modulation, erythrocyte
production, and neural functions (Kant and Block, 1990). It also plays role in the
treatment of various chronic diseases such as sickle cell anemia and cancer
(Kolasa, 1993). Potassium is a predominant mineral found in the potato tuber
(Yilmaz et al., 2005). It helps to regulate inter and intra cellular fluids and mineral
balance thus helps to overcome hypertension in patients. In addition also found
vital in transmitting nerve impulses and helping muscular contraction.
2.4 POLYPHENOLS
Polyphenols are the commonly occurring secondary plant metabolites
primarily associated with the antioxidant activity as verified by in-vitro lipid
oxidation model (Kaur and Kapoor, 2002). More than 8000 phenolic structures
have been indentified so far being as simple as phenolic acid to highly complex
tannins (Harborne, 1998). They are synthesized in the plant metabolism through
shikimate pathway and acetate pathway (Bravo, 1998). Phenolics are vital for plant
development, reproduction and connected to diverse role such as protein synthesis,
enzyme biosythesis, anti-pathogen, anti tumour and aids in the detection of
symbionts. They also protect live plants against oxidative stress and promote
healing (Shahidi and Naczk, 1995).
Phenyl alanine acts as precursor in phenol biosynthesis, primarily mediated
through the activity of Phenylalanine Ammonia Lyase (PAL) which catalyses the
deamination of phenylalanine (Hamauzu, 2006). Phenolics exist in diverse
configuration as free, glycosylated, polymerized forms (Naezk and shahidi, 2004)
however the basic compositional feature of phenolics is diphenyl propane moiety
that comprises of two aromatic rings linked through three carbon atoms forming an
17
oxygenated heterocycle i.e; phenol subunit (Teixeira et al., 2005). They are present
either as simple phenols (one phenol sub units), poly phenols (two phenol subunits)
or tannins (three phenol subunits). Phenolic acid is the carboxylic derivative of
phenol which is also associated with the sensory attributes and antioxidant
potential in foods (Robbins, 2003).
Polyphenols have strong antioxidant potential in neutralizing and
quenching free radicals by donating electrons and forming phenoxyl radicals which
are relatively inert and do not instigate further radical reactions (Fernandez et al.,
2004). They act as terminator of free radicals and chelator of metal ions capable of
lipid peroxidation (Schroeter et al., 2002). Milde et al. (2007) reported that
polyphenols along with carotenoids prevent the oxidation of Low Density
Lipoproteins thus preventing from atherosclerosis and related disorders. Owing to
its significant antioxidant capacity the role of phenolics in human health is
increasingly being realized. The protective effect of diet rich in fruits and vegetable
against degenerative diseases is largely attributed to the presence of phenolic
compounds (Manach et al., 2005). Regular intake of diet rich in phenolics has been
linked to lower rate of cancer and cardiovascular diseases (Seeram et al., 2005).
Considerable diversity of phenolic compounds present in potato tubers having
major phenolics as gallic acid, chlorogenic acid, caffeic acid (Niggeweg etal.,
2004) while minor includes ferulic acid, rutin, quercetin, kaempferol etc. (Nara et
al., 2006). In addition purple and red fleshed potato varieties also includes
petunidin, p-courmaric, pelargonidin (Reyes, 2005). Despite having moderate
phenolic contents potato exhibited potato exhibited the second best inhibitory
action on low density lipoprotein oxidation between 23 different vegetables studied
(Vinson et al., 1998).
18
2.5 ANTIOXIDANTS
Antioxidants are the compounds which have the capacity to quench free
radicals and protect the biological systems against their potential detrimental
effects (Diplock, 1998). Free radical produced in the biological system due to
different physiological processes like oxidative stress, senescence etc induces
loss of nutritional quality of fruits and vegetable during post harvest storage
(Antolovich et al., 2001). Oxidative stress induced by these free radicals in the
form of super oxide anions (O-2), Hydrogen peroxide (H2O2) and Hydroxyl
Radicals (OH-) considered to be the key factors in various degenerative diseases.
Free radicals are the molecules having one or more unpaired electron which confer
them considerable degree of reactivity. They are omnipresent and generated in
normal physiological processes like respiration, pathogenic activity, inflammatory
cell activations, mutations etc. (Hussain et al., 2003).
Free radicals are present either as reactive nitrogen species (RNS) or
reactive oxygen species (ROS) and capable of damaging extensive range of
oxidizable substrates like DNA, Proteins, Lipids, and Carbohydrates (Haila, 1999).
Reactive oxygen species (ROS) can physiologically transform DNA, producing
single/ double-stranded DNA fragments, base or sugar modifications, hold or
stimulation of transcription, and genomic instability (Poli et al., 2004). Reactive
nitrogen species (RNS) like nitrogen oxides and peroxynitrites have also been
involved in DNA modifications. In addition, different redox metals capable of
producing free radicals, and non-redox metals having potential to bind critical
thiols, facilitates the mechanism of carcinogenesis (Leonard et al., 2004). Valko et
al. (2001) observed that ferous-induced stress is believed to be a primary cause of
human colorectal cancer. The production of ROS and RNS inside the biological
19
system leads to the chemical modifications of important macromolecules. Anti
oxidants have the capability to avoid such modifications and avert the beginning of
oxidizing chain reactions (Velioglu et al., 1998). They quench free radicals by
conferring electron or hydrogen, neutralizing the singlet oxygen and deactivation
of metal ions (Shahidi, 2002).
Antioxidants are broadly classified as non enzymatic (free radical
scavengers like ascorbic acids, phenolics, flavonoids, tocopherols) or
enzymatic (inhibit peroxidase reactions like superoxide di-mutases,
glutathione peroxidases) in nature (Nzaramba, 2007). On the basis of their origin
they are characterized as synthetic or natural. Butyl hydorxy toluene (BHT) and
Butyl hyroxy anisole (BHA) are the examples of synthetic antioxidants having
phenolic structures with different alkyl substitution. However the uses of these
synthetic antioxidants are assumed to cause carcinogenity thus being restricted to
use in food stuff (Koleva et al., 2002). Thus need arises to replace these synthetic
antioxidants with naturally occurring antioxidants. Natural antioxidants constitutes
wide range of compounds like, phenolic compounds (Flavonoids, phenolic acids,
gallic acids, anthocyanins), nitrogen compounds (alkaloids, amines, amino acids),
Carotenoids, Ascorbic acids, tocopherols etc (Shahidi, 2002). Most of these
antioxidants are of food origin and termed as dietary antioxidants.
Significant antioxidant activity has been identified in the peel (Singh and
Singh, 2004) and flesh (Lachman et al., 2008) of potato and thus considered to be
an important source of dietary antioxidants. Being major staple crop in most part of
the world utilization of potato as an alternate source of synthetic antioxidant will
be very effective against different chronic disorders. Their regular intake of dietary
antioxidants can prevent from diabetes, cardiovascular diseases, carcinogenesis,
20
neurological disorder and ageing (Makazan et al., 2007). Highest anti oxidant
activity has been estimated in purple skinned varieties followed by moderate
and lowest activity recorded in red skinned and yellow skinned potato
varieties respectively (Li et al., 2006).
Antioxidant assays largely depends on their effects through different
mechanism and specified functions. Different assays have been developed to
measure the antioxidant activity. Their mode of action is either as electron transfer
reaction based assay and hydrogen atom transfer reaction based assay. Electron
transfer reaction based assays include trolox equivalence antioxidant capacity
(TEAC), ferric ion reducing antioxidant power (FRAP), 3-ethyl-benzothiazoline-6-
sulfonic acid (ABTS) and 2, 2 Diphenyl -1-picryl hydrazyl (DPPH). Hydrogen
atom transfer reaction based assays are total radical trapping antioxidant parameter
(TRAP) and oxygen radical absorbance capacity (ORAC) (Huang et al., 2005).
The most frequently used assays are DPPH and ABTS radicals because of their
simplicity, swiftness and sensitivity (Arnao et al., 1999).
2.6 POLYPHENOL OXIDASE (PPO)
Enzymes are necessarily required in cellular metabolism for regulating key
biochemical reactions and their working mechanism is required for understanding
the chemical basis of life. They lower down the activation energy required for the
particular biochemical reaction and facilitate the formation of enzyme-substrate
complex. Being biological catalysts they are highly specific, usually required in
small amount and their activity is measured by the quantity of reaction product.
Polyphenol Oxidase (PPO) is also called as phenol oxidase, tyrosinase,
catechol oxidase, mono phenol oxidase and diphenol oxidase. Enzymatic browning
21
initiated in fruits and vegetables due to multiple reasons like mechanical injuries
(cutting, wounding and bruising), storage disorders (chilling and freeze injuries) or
by physiological reasons (ripening and senescense) (Crumiere, 2000). PPO activity
increases with the increase in physiological stages and becomes highly pronounced
during senescence, and under stress conditions. Thus the activity is the significant
index of post harvest storage life in horticultural produce.
Enzymatic browning causes nutritional and sensorial loss in horticultural
commodities and primarily mediated through the activities of the group of enzymes
termed as Poly phenol oxidases (Anthon and Barrett, 2002). These enzymes
catalyze reaction between colourless polyphenol molecules (Catechol) and
molecular oxygen forming orange coloured benoquinone which spontaneously
cause the formation of dark coloured complex called Melanins (Ding et al., 1998).
The polyphenol oxidase (PPO) activity using catechol (polyphenol) as substrate is
described as under:
Catechol + Oxygen ----------- Benzoquinone + water ------------- Melanin
The formation of dark colored pigment (melanin) however, confers
antimicrobial properties to the fresh produce and their colour intensity is reliant on
the kind of substrate and environmental conditions (Nicolas et al., 1994).
Polyphenols are present in fruits and vegetables in diverse forms like Gallic acid,
flavonols, benzoic acid, cinnamic acids, chlorogenic acids etc. and most of them
acts as substrate for polyphenol oxidase activity (Crumiere, 2000). Yemenicioglu,
(2002) reported that polyphenol oxidase activity can be controlled in Russet
Burbank potatoes by mild heat treatment at 50oC. He reported significant reduction
(25-45%) in enzyme activity with appreciable sensorial parameters while
22
blanching at above temperature for 60 minutes. The technique have been found as
better alternative to sulphitation for browning control in potatoes.
Controlled browning is often required in different food processing
operations to promote desirable sensorial attributes in the finished products. The
coloured intensity for the specific product development is regulated by the amount
of enzymes and its respective substrate. The processing quality of prunes, black
raisins, figs, tea, cocoa and coffee is largely dependent on the presence of their
indigenous polyphenol oxidase activity (Walker, 1995).
2.7 PER OXIDASES (POD)
Peroxidases are also related to the browning of fruits and vegetables
primarily mediated through the break down of hydrogen per oxides (H2O2)
(Loaiza-Velade and Saltveit, 2001). They along with catalase cause the formation
of free radicals and oxygen however unlike catalases they are of different types and
require specific substrate (R) for their activity.
2H2O2 → 2H2O +O2 (Catalase)
H2O2+ RH2 → 2H2O+ O2 (Peroxidase)
Peroxidase catalyses different metabolic functions like auxin catabolism,
bridge formation between cell components, alcohol oxidation and cause the
formation of different metabolites like lignin and suberin (Lejaa et al., 2003).
Nevertheless peroxidase and polyphenol oxidase are the major enzymes
responsible for quality loss in horticultural produce due to phenolic dilapidation
(Francois and Espin, 2001). The liberation of free radicals in response to their
23
enzymatic activity reacts with unsaturated fatty acids and cause the formation of
membrane lipid peroxidation in intra cellular organelles eventually leads to the
cellular desiccation, electrolyte leakage and cellular mortality (Scandalios, 1993).
POD activity increases in fruits and vegetables under stress conditions and
with the progression in their physiological stages i.e ripening, senescence etc
(Aydin and Kadioglu, 2001). El-hilali et al. (2003) reported increase in peroxidase
activities under storage condition in mandarin and the same have been reported by
Setha et al. (2000) in papaya. Anthon and Barrett, (2002) studied the thermal
stability of different enzymes in potatoes at temperature ranges between 60-85oC.
He declared peroxidase being most resistant one followed by pectin methyl
esterase, polyphenol oxidase, and lipoxygenase. This makes peroxidase the
selective enzyme in fruits and vegetables post harvest studies being thermal stable
and omni present in plant parts. The inactivation of peroxidase provides reasonable
assumption of natural safety that the other quality related enzymes have also been
inactivated. Hence peroxidase activity has also been commonly employed as an
indicator of appropriate blanching in freezing industry.
2.8 PACKAGING SYSTEMS
Fruits and Vegetables are high moisture commodities and thus require
appropriate post ha8rvest techniques to prolong their storage life. Use of suitable
packaging systems extends the storage life by protecting the perishables during
transit, slowing down the ripening process during post harvest storage and
conferring value addition during marketing (Kittur, 1998). The primary advantage
of packaging is that the stored product maintains its novelty and eating quality as
24
compared to those stored in air. The stored commodities can fetch premium price
in the market only if the quality and quantity of the competing product is poor. The
efficient marketing tactic can recuperate the supplementary packaging costs with
rational profit (Maria, 2007).
Packaging is a vital component of post harvest supply chain management in
horticultural crops. In Pakistan and other developing countries large jute bags
(mostly expired cereal bags) with carrying capacity of 80-100 kg are being utilized
for potato packaging. The present uses of such poor quality second hand bags are
responsible for the disease indicence followed by the bulk of commodity loss
during transportation and storage. In this regard no systematic effort has yet been
carried out to study the response of indigenous potato crop to the type and
permeability of different packaging materials. The quality oriented packaging
system like polyethylene, polypropylene, polystyrene, bio degradable plastics,
corrugated cartons, cushioning materials are required in compliance with food
safety standards to compete the international market for valuable foreign exhange.
Fruits packed in modified atmosphere packaging decrease the consumption
of respiration substrates i.e organic acids and sugars thus preventing the quality of
produce (Ding et al., 2002). Low oxygen and high carbondioxide levels decreases
rate of respiration, restricts ethylene production, curb enzymatic reactions,
minimize physiological disorders and eventually conserve the eminence of the
perishables. Browning disorders and tissue senescence can efficiently be inhibited
by decreasing oxygen and increasing carbon dioxide in the storage atmospheres
(Robert et al., 2003) in addition elevated carbon dioxide also reduces the effect of
ethylene especially in climacteric fruits (Mathooko et al., 1995).
25
The influence of MAP on horticultural commodities varies with gaseous
exhange, storage period, variety and packaging permeability (Rakotonirainy et al.,
2001). Reduced oxygen (<2%) in storage atmosphere however effects
tricarboxylic acid cycle (TCA) as a consequence of anaerobic respiration.
Unoxidized pyruvic acid accumulation resulted into ethanol formation with
subsequent off flavor development and tissue disintegration (Kays, 1991).
Therefore changes in oxygen and carbon dioxide levels should be under significant
threshold level (Beaudry et al., 1999). This can be achieved by establishment of
suitable packaging system with appropriate permeability to avoid anerobiosis
during the post harvest storage.
Transition in the quality attributes of horticultural commodities under
different packaging systems have been an important point of interests for the
researchers. Potato storage under controlled atmosphere is not recommended due to
the increased rate of respiration under high carbon dioxide level (Fonseca et al.,
2002). On the other hand extremly low oxygen level leads to the onset of anaerobic
respiration followed by tissue breakdown and off flavor development (Kays, 1991).
Packaging has been considered as best alternate for potato storage by employing
modified atmospheric condition around the stored tubers. The prevention of off
flavor development due to the efficient packaging also proved to be advantageous to
get superior quality processed products.
Different types of packaging systems have been employed to minimize post
harvest losses in potato. Rosenfeld et al. (1995) employed different types of
packagings like polyester, mesh, colored paper and polyethylene bag for “Beate”
potato variety under 5°C and 23°C temperature for 1 and 2 weeks storage. The
26
highest Glycoalkaloid contents at elevated temperature were observed in all
packaging systems. Blue colored polyethylene attained maximum while black
colored polyethylene maintained minimum glycoalkaloid contents. Gosselin and
Mondy, (1989) packed Russet Burbank and Cheftain potato varieties in paper and
polyethylene bags and evaluated their physico-chemical parameters at an interval of
1, 4 and 8 weeks. He reported that the potatoes packed in polyethylene were lower in
weight loss and ascorbic acid and showed higher polyphenols and glycoalkaloids
contents than those packed in paper during the storage at 20 oC. Similar information
was reported by Abong et al. (2011) who found significant difference in the
ascorbic acid contents in four Kenyan potato varieties during post harvest storage.
He found significant reduction in ascorbic acid contents in potato strips during
harvest, packaging, storage and processing. Shetty et al. (1999) layed the
guidelines for the prevention of soft rot, dry rot and silver scurf diseases in freshly
packed potato. Careful harvest, gentle handling, sorting, washing, drying and
packaging at temperature 45-50 oF should be carried out to avoid disease
proliferation during storage and transportation.
Oner and Walker, (2011) investigated the effect of modified almosphere
packaging on the quality attributes of refrigerated potato strip prior to processing.
He concluded that two step blanching (60 and 98oC) of potato strips followed by
aseptic packaging increased the storage life of potato strips with appreciable post
processing attributes. Baskaran et al. (2007) demonstrated improved quality
attributes in minimally processed potato cubes stored under modified atmosphere
packaging in conjunction with low dose gamma irradiation. Beltran et al. (2005)
studied different sanitizers like water; sodium hypochlorite, sodium sulfite,
27
ozone Tsunami, and the combination of ozone–Tsunami were evaluated on
microbiological and sensorial characteristics of fresh cut potato in modified
atmosphere packaging. The combination of Ozone-Tsunami under modified
atmosphere packaging has been found the most capable treatment against
microbial load.
Packaging systems decreases weight loss and increase ascorbic acid in
tomato (Sammi and Masud, 2007, Badshah et al., 1997) however under prolong
storage duration low ascorbic acid contents have also been reported (Batu and
Thompson, 1998). The application of calcium chloride and potassium
permanganate along with packaging materials has been reported to increase the
storage life in tomatoes (Saammi and Masud, 2007) and apricots (Ishaq et al.,
2009). Alsadon et al. (2004) studied tomato packaging at three different
temperature regimes i.e. 5°C, 15°C and 25 °C and 97% relative humidity.
Maximum storage life was observed at 5°C while higher fungal decay and fast
color development were reported at 25°C. Improved post harvest storage life was
also observed in peach cultivars (O Henry’ and ‘Elegant Lady’) under modified
atmosphere packaging (Zoffoli et al., 1997). Similar observations were recorded
for packed peaches cultivar i.e. Yumyeong at 0 ◦C for 4 weeks storage with higher
electrical conductivity than the control (Choi and Koo, 1997). Das et al. (2006)
studied the effect of MAP and controlled atmosphere (CA) on the accurance of
Salmonella Enteritidis in cherry tomatoes. He found increased mortality rate of S.
Enteritidis on tomato surface that were stored in MAP than those placed in
Controlled atmosphere and air. He concluded that modified atmosphere packaging
is effective in preventing microbial and insect contamination
28
Different packaging systems are commonly supplemented with low
temperature storage (Kyriacou et al., 2009), sprout inhibitors/suppressants (Frazier
et al., 2004), ethylene scavengers (Abbasi et al., 2004), edible coatings (Khuyen et
al., 2008), irradiation (Blessington et al., 2007) etc. in formulating an integrated
strategy to minimize post harvest losses. In addition these packaging materials are
processed into sheets, wraps, pouches and containers by employing different
processing operations providing barrier properties during physiological gaseous
exchange (Hong et al., 2003). Modified atmosphere packaging (MAP) has been
found effective in quality persistence of horticultural commodities under post
harvest storage (Beaudry, 1999) and found inexpensive as compare to Controlled
atmosphere storage (Tuil, 2000). It is employed in the storage of fruits and
vegetables by using plastic films which restrict the exchange of respiratory gases,
primarily increases carbon dioxide and decreases oxygen around the produce
eventually prolonged the storage life (Sanchez et al., 2003). In general packagings
can be employed around fresh fruits and vegetables in two different confirmations.
Firstly to establish a modified atmosphere passively by employing packaging
material of suitable permeability and secondly to create modified atmosphere
actively by flushing out the air from the packaging material with specified gas
mixture. The purpose is to maintain an optimum level of gases inside the
packaging causing a decrease in respiration with out being detrimental to the
product quality (Durand, 2006).
Different types of packaging materials with specific permeability have been
employed for horticultural produce. The plastic packaging had better effect against
weight loss, retards hardening and had similar impact on quality parameters as
29
edible coatings. The combined effect of plastic packaging along with different
edible coating can be effective in storage stability of horticultural commodities.
Polyethylene packaging has been extensively used for providing modified
atmosphere around fruits and vegetables. They are of different types like High
Density Polyethylene Pcakaging (HDPE), Medium Density Polyethylene
Packaging (MDPE) and Low Density Polyethylene Packaging (LDPE). The use of
proper type depends on the type of produce and storage conditions. HDPE has high
tensile strength and low cost but limits gaseous exchange however the use of
LDPE is preferred for their application in tomatoes (Alsadon et al., 2004) owing to
its improved gaseous exchange, better flexibility and good clarity (IQS, 2005).
Polypropylene based bag and bio based polymeric matrix were used to pack the
cherry fruits and investigations revealed that oriented polypropylene based bag
displayed best results under normal atmospheric conditions (Conte et al., 2009).
The modification in different packaging materials has been reported especially in
the produce having high rate of respiration. This is carried out by introducing pores
of defined size and number in the packaging material (Exama et al., 1993). The
packaging modification can also be achieved by amalgamation of ethylene & vinyl
acetate oriented polypropylene and low density polyethylene, which resulted in
achieving excellent results for storing the produce over a long period of time. The
incorporation of sorbic anhydride in polyethylene packaging film along with its
antimycotic potential has also been demonstrated by Weng and Chen, (1997).
The use of synthetic packaging being of petroleum origin and non-
biodegradable nature pose many ecological problems. So efforts should be carried
out to convert or replace plastic packaging into biodegrable and environmental
30
friendly packaging. The organic raw materials like starch, cellulose, proteins,
chitin/chitosan can be used as better alternative. The use of Chitosan application
was found useful in lowering respiration rate, reduced polyphenol oxidase activity,
delayed colour change, decreased weight loss and inhibition of the post harvest
decay in longan fruit (Jiang and Li, 2001). Another pattern of using biodegradable
packaging is the cross linking of natural polymers with synthetic monomers.
Nevertheless due to rapid industrial growth and food security issues practically it
seems impossible to completely replace the synthetic plastics.
2.9 POTATO GREENING
Formation of chlorophyll in cortical parenchyma due to light exposure
results in undesirable greening process (Pavlista, 2001) and is also associated
with public health concerns due to the formation of toxic glycoalkaloids and
economic loss during marketing. Unlike glycoalkaloids, chlorophyll is non
toxic however greened potatoes are of poor economic value and considered
unfit for human consumption (Percival, 1999). Light and mechanical damage
are the most imperative post harvest factors affecting the synthesis of
glycoalkaloids in potato tubers (Plhak and Sporns, 1992).
The phenomenon of potato greening is usually avoided by the farmers in
Pakistan during early morning harvest there by preventing them from exposure to
direct sunlight as also suggested by Woolfe, (1987). The harvest is usually
followed by on farm storage in pits by the farmers or in dark cold storage by the
processor. However exposure of potato tuber to light during post harvest
handling and marketing is inevitable specifically during their retail display in
31
super stores under intensive illuminations. Comprehensive study of tubers
response to different colored light along with the transition in their quality
attributes is required to identify the best illumination for indigenous premium
potato variety for retail display storage where ever required in the local and
export market.
Potato stored under different light types showed variable physiological
responses. The effect of indirect sunlight, fluorescent light, storage in darkness
under room temperature and storage in darkness under refrigerated conditions
was investigated for 14 days on the total glycoalkaloid content of potato tubers
(Rita et al., 2007). Highest chlorophyll and glycoalkaloids contents were
reported in the fluorescent light with steady increase through out their storage
period. Irrespective of light and temperature source small sized tubers attained
higher chlorophyll and glycoalkaloids concentrations. Edward and Cobb,
(1996) investigated that the potato tuber exposure to direct sunlight in field
and fluorescent light in super market increases the chlorophyll and
glycoalkaloids production. Tuber exposure to sunlight, fluorescent,
ultraviolet, and luminous lights after harvest, during storage, transit and
marketing causes chlorophyll and glycoalkaloids accumulation thus poses
main concerns to producer, processor and consumer (Percival, 1994). The
influence of light sources on different potato varieties during storage has been
investigated by Sengul et al. (2004). Potato tubers from Marfona and Granola
varieties were separated as normal, greened, wounded and sprouted. Potatoes
storage was carried out in normal store dark, normal store light, retail
32
refrigerator dark and retail refrigerator light. They observed that high
temperature; light, physical damages and post harvest handling were
significant factors responsible for the accumulation of glycoalkaloids
concentrations ranged between 0.66-32.76 mg/kg f.w in different tubers. The
response of different potato varieties (Kerrs Pink, King Edward and Desiree)
under different light source (low pressure mercury, high pressure mercury,
high pressure sodium and Fluorescent warm white) has been reported by
Percival et al. (1993). He concluded that glycoalkaloid and chlorophyll
contents were found maximum in King Edward and higher glycoalkaloid and
chlorophyll contents were recorded in sodium and fluorescent lights as
compare to those placed under low and high pressure mercury lights.
The influence of light duration on the potato tubers have also been
reported by Zrust et al. (2001). He found two fold increase in glycoalkaloid
contents in potato varieties under light exposure for 14 days (68.6 mg kg-1)
than those placed for 7 days (33.1 mg kg-1). The simultaneous increase in
chlorophyll and glycoalkaloids contents under prolong exposure to light
sources has also been reported (Griffiths et al., 1994).
The effect of different temperatures (5, 10, 20 and 25°C) on chlorophyll
and glycoalkaloids accretion in potato cv. King Edward under low photon density
has been studied by Edwards and Cobb, (1997). The maximum chlorophyll
contents were indentified at 20 °C while the concentration of glycoalkaloids
remained unaffected under different temperature regime.
33
2.10 POTATO GLYCOALKALOIDS
Glycoalkaloids (GA) are predominantly found in different species of
family solanaceae i.e potatoes (Solanum spp.), tomatoes ( Lycopersicon
spp.), egg plant (aubergines spp.) etc. however some of them are also
present in non solanaceous plants like apple, sugar beet, cherries
etc.(Friedman, 2006). They are the naturally occurring toxic compounds in
potato reported to have anti microbial, anti fungal and insecticidal properties
contributing to the immune response of the crop against different diseases,
pests, insects, and animals (Rodriguez-Saona et al., 1999). GA are present in
different parts of potato plant like flowers, young leaves, tubers, eyes, peels
and sprouts however, its maximum amount is present in the tuber peripheral
layer and periderm cell parenchyma (Friedman et al., 2003).
Total glycoalkaloid are present in the forms of α-solanine (C45 H73 NO15,
Mol wt. = 868.07) and α-chaconine (C45 H73 NO14, Mol. Wt = 852.07) contributing at
least 95% of the total in potato. Both of them are structurally alike, holding a same
aglycone (solanidine), Carbohydrate moiety in α-solanine is composed of glucose,
galactose and rhamnose (β-solatriose), while in α-chaconine is of glucose,
rhamnose and rhamnose (β-chacotriose) (Nema et al., 2008). Cholesterol has
been considered as the precursor of GA synthesis in potato which is present as
the major sterol present in the potato. Biosynthesis of Solanidine is believed to be
associated with cholesterol which causes the formation of α-solanine and α-
chaconine by galactosylation or glucosylation respectively (Smith et al., 1996). The
ratio of concentration of α-solanine and α-chaconine depends on the variety,
anatomical plant parts, agronomic practices and ranges 1:2 to 1:7 (Bejarano,
34
2000). The development of GA is related with the potato greening, however no
metabolic link has been identified between chlorophyll and GA biosynthesis
(Edward and Cobb, 1997).
The quantity of glycoalkaloids in food is attributed to its medicinal or
toxicological properties. Low quantities (below 15mg/100g f.w) impart
flavor and functional value, while high quantities (above 20 mg/100g f.w)
can impart bitter taste and even may even cause death at excessive intake (28
mg/100g f.w) (Mensinga et al., 2005). Joint WHO/FAO expert committee on
Food additives (JECFA, 1993) established 10mg/100g fw of GA intake as of
no adverse effect level however; the upper safe limit for their intake is
suggested at 20mg/100g f.w (Papathanasiou et al., 1999). This upper safe
limit has been established for acute toxicity and does not correspond to
possible chronic disorders therefore the upper limit recommended at 5-7
mg/100g TGA in potato cultivars suitable for human consumption (Valkonen
et al., 1996).
The primary effects of GA toxicity in human metabolism appear in
the gastrointestinal tract characterized by diarrhea, vomiting, and abdominal
pain (Patel et al., 2002). The secondary toxicological effects of GA are
associated with different neurological disorders like paralysis,
bronchospasm, cardiac failure, dizziness, headache etc. GA affects the
nervous system firstly by the disruption of membranous phospholipids and
secondly by the inhibition of acetyl cholinesterase activity, an enzyme
responsible for acetylcholine regulation, a compound required for nerve
impulses conduction (Mensinga et al., 2005). The intake of GA in human
35
diet under permissible limits has also been associated with some beneficial
effects. They are reported to posses anti allergic, anti inflammatory (Choi
and koops, 2005), anti cancer (Lee et al., 2004), anti asthma (Dorland, 1994)
and cholesterol lowering effects (Friedman, 2006).
The formation of GA in potato during pre and post harvest period is
dependent on several factors like cultivars, environment, harvesting
conditions (temperature and time), physiological stages (maturity,
sprouting), phytopathogens, mechanical injuries (bruising, wounding), Light
(intensity, duration, wavelength), packaging (color, type, permeability) etc.
(Nema et al., 2008). The proper management of all these factors can keep
the formation of this toxin under permissible limit. GA in the potato tubers
are not destroyed during boiling, baking and frying however, they are
reduced during different processing operations (peeling, cutting, dicing etc)
involved in the production of value added products like chips, French fries
(Peksa et al., 2006).
2.11 LOW TEMPERATURE SWEETENING
Improper storage of vegetables is very critical in under developed
countries due to poor transportation and high temperature that favors decay rather
than storage. Natural physiological processes (ripening, respiration, evapo-
transpiration), physical damages, microbial invasion limits the storage life of the
fresh produce. These all factors are directly or indirectly influenced by different
temperature variables. Temperature is most important factor in determining the
post harvest quality and life under storage (Bachmann and Earles, 2000). Low
36
temperature slows down the enzymatic activities, hinder respiration rate, retard
softening and determine the final nutritional composition (Madhavi and
Salunkhe, 1998). Keeping horticultural commodities under low temperature
storage is therefore a very efficient technique to reduce the post harvest losses;
however its optimum range for specific produce is very much critical to avoid
various disorders like, Chilling injury, freeze injury, and the most important
being potato specific low temperature sweetening etc.
Potato storage under low temperature is employed to extend the post
harvest storage period by extending the natural dormancy through an imposed
dormancy (Wiltshire and Cobb, 1996). Generally in commercial storage, after
curing (stimulation of suberization and wound healing) tubers are purposely
stored at 3-5°C for seed, at 6-9°C for fresh market and at 10-15°C for processing
(Western Potato Council, 2003) however, their storage temperature is largely
related with the undesirable hexose accumulation termed as low temperature
sweetening (Tamaki et al., 2003).
Low temperature sweetening in potato tubers starts with in few days and
is characterized by the degradation of starch polymers into sucrose due to
inactivation of glycolytic enzymes (Phosphofructokinase and fructose-6-
phosphate phosphotransferase). Sucrose is further hydrolyzed into glucose and
fructose by the activity of enzyme invertases (Sonnewald, 2001). Reducing
sugars accumulation in potato tubers during low temperature storage is of prime
industrial concern due to its participation as substrate in maillard reaction at
elevated temperature. The high level of reducing sugars gives rise to
commercially unacceptable brown crisp color (Blenkinsop et al., 2002). Kumar et
37
al. (2004) reported that the brown chip color in the potato tubers can be reversed
to some extent by reconditioning them at warmer storage temperature (> 15oC)
before frying. At intermediate temperature sugars are converted back into starch,
or metabolized as respiratory substrate. However the process of reconditioning is
cultivar dependent and does not alleviate the sugars at acceptable level especially
in case of senescent sweetening and considered to be irreversible (Knowles et al.,
2009).
In order to maintain desirable processing quality in selected potato variety
proper temperature management is very important under prolonged storage. The
optimum storage temperature for the premium potato variety “Lady Rosetta”
grown under indigenous conditions is required as the foremost investigation for
the potato growers in the country. Changes in different vital attributes
(especially sugar metabolism) in the premium potato variety under
comparative temperature regimes are of great concern for the processor to
develop export quality product.
2.12 SUGAR
The level of sugars in potato tuber is an important quality attribute with
special reference to post processing browning. The amount of total sugar contents
ranges between trace amounts to 5 % of dry matter (Kyriacou et al., 2009). These
are primarily present in the form of non reducing sucrose and reducing fructose
and glucose (Blenkinsop et al., 2002). Though the role of sucrose in browning is
limited however it serves as precursor for the assembly of reducing sugars
mediated through storage activated enzymes i.e invertases (Kumar et al., 2004).
38
Reducing sugars are present in the form of Aldoses carrying aldehyde functional
group i.e. glucose or in the form of ketoses carrying ketone as functional group
i.e. fructose (Fennema, 1996). The processing quality of potato tuber is however
associated with the presence of reducing sugars being considered as an index of
proper frying color. Non-enzymatic browning during maillard reaction in
processed potato products is associated with the production of neurotoxin acryl
amides (Dewilde, 2006) which is of grave food safety concern.
Different pre harvest factors have been reported to effect the sugar
accumulation in potato during storage like genotype (Gaur et al., 1999), Soil
moisture (Eldredge et al ., 1996), soil nutrients ( Kolbe et al., 1995) temperature
during growth (Pavlista and Ojala, 1997) tuber maturity ( Hertog et al., 1997),
and mechanical stress (Hironaka et al., 2001).
Edwards et al. (2002) reported storage temperature being the major post
harvest factor influencing potato sugar profile. He found minimum sucrose,
fructose and glucose contents at 10 oC storage as compare to those placed at
3.3oC and 8.3oC temperature regimes and also found decline in sugar contents in
potato upon reconditioning. Other post harvest factors may include tuber
dormancy (Fauconnier et al., 2002), senescent sweetening (Wiltshire and Cobb,
1996) and storage temperature (Zhou and Solomos, 1998).
Different assays have been developed to estimate the different sugar
fractions in potato tubers like Lane and Eynon titration method (AOAC, 1990),
colorimetric method (Nourian et al., 2002), high performance liquid
39
chromatography (Rodriguez-Saona and Wrolstad, 1997) and glucose reagent
strips (Martin and Ames, 2001).
2.13 POTATO SPROUTING
Sprouting during the post harvest storage results in extensive economic
losses due to increased weight loss and reduced tuber quality. Sprouting reduces air
flow through the piles under storage thus elevates the average temperature
consequently increases the chances of disease attack and reduced storage life.
Since low temperature storage (4-15°C) is carried out for potato hence sprouting is
also known to be associated with the swift conversion of starch into sugars which
confer substantial commercial loss to the commodity (Sonnewald, 2001).
Sprouting in potato tubers can be prevented either by prying with dormancy
breaking processes using different sprout inhibitors like CIPC, IPC etc. or
restricting the development of meristems by using different sprout suppressants
like essential oils, hot water treatment etc.
Chloro isopropyl N- phenyl carbamate (CIPC) or chloropropham is one of the
most widely used sprout inhibitor for potato which inhibits sprouting by interfering
with mitotic cell division. It disrupts the spindle formation and eternally damages
the meristems (Kleinkopf et al., 2003). It has been applied in storage atmosphere
as thermal fog, spray, dust etc. (Frazier et al., 2004) however its application
should remain under the acceptable EPA (Environmental Protection Agency)
residual level (> 50 ppm). Chloropropham is occasionally used as a mixture with
propham (isopropyl N-phenylcarbamate or IPC) which has the faster but similar
sort of action as CIPC and assumed to achieve better sprout control (Meredith
40
1995a). CIPC application as single dose can attain long-term sprout inhibition, and
often being applied before natural dormancy release in potato tubers under storage
(Frazier et al., 2004). CIPC application is however associated with growing health
concerns related to their potential adverse impacts on human health, as it may
potentially damage erythrocytes, kidney, liver and spleen (Nakagawa et al., 2004)
in addition it has also been related to the ozone depletion (Kerstholt et al., 1997).
The increasing health and environmental concerns have reduced the permissible
residue limits from 50 to 30 ppm in United States on fresh potatoes (Kleinkopf et
al., 2003) and need has raised for safer alternative.
Maleic Hydrazide (MH) is applied as pre harvest sprout inhibitor in potato
crop after the tuber cell division is completed and is translocated from stems and
leaves to the developing tubers (Wiltshire and Cobb, 1996). It is an isomer of
nitrogenous base uracil and believed to interfere with the mitotic cell division.
Tecnazene (1, 2, 4, 5-tetrachloro-3-nitrobenzene) is another volatile sprout
suppressant which is applied as a powder during the potato storage. It appears to
prevent mitotic cell division however the efficacy may be reduced after tubers have
broken dormancy (Meredith, 1995b).
Essential oils and their major components are increasingly being used as
Potato Sprout Suppressants. The environment and food safety concerns regarding
the use of different sprout inhibitors have created need for safer alternatives
primarily as the essential oils extracted through natural sources (Oosterhaven et
al., 1995). Volatile oils have been employed since long in most of the parts of
world for the sprout inhibition in potato. The potatoes were known to bury in pits
covered with leaves of muna (Minthostachys glabrescens) and soil in the Latin
41
American countries like Argentina, Peru etc. for sprout inhibition (Vaughn and
Spencer, 1993). These volatile oils are less noxious imparting peculiar odor of
their parent source (Buchanan et al., 2000) served as defense mechanism against
microbial and insect loads (Rajendran and Sriranjini 2008) and also being used in
aromatherapy, colognes, and cooking spices (Vaughn and Spencer, 1991).
Vokou et al. (1993) reported that different aromatic plants like spearmint
(Mentha spicata L), penny royal (Mentha pulegium L), rosemary (Rosmarinus
oficinalis L.) and sage (Salvia fruticosa L) rich in essential oils like carvone,
pulegone, and 1,8-cineole were found effective against potato sprout inhibition. He
further added that the application of essential oils only interfere with the growth
and elongation of emerging sprouts thus precisely be called as sprout suppressant
rather sprout inhibitors. Oosterhaven, (1995) identified oil extracts from aromatic
plants like pepper mint (Mintha piperita), caraway (Carum carvi L.) and dill
(Anethum graveolens L.) as potent sprout suppressant for potato. Aromatic plants
like, Japanese mint (Mentha arvensis L., rich menthol contents), lemongrass
(Cymbopogon flexuosus L., high in citral) (Farooqi et al., 2001) and basil
(Ocimum americanum L., elevated linalool contents) (Singh et al., 1997) were
also reported to carry suppressing effects against potato sprouting during storage.
In addition to their sprout suppressing effect essential oils also been reported to
carry significant fungicidal (Gorris et al., 1994), bactericidal (Vokou et al., 1993)
and insecticidal (Isman, 2006) characteristics thus prolonged the post harvest
storage life of potato.
Essential oils are the secondary metabolites primarily present as terpenoids
and phenylpropanoids produced inside the epidermal and mesophyll tissues of
42
plant in the special morphological modifications like secretory glands, resin ducts
etc. The principal components present in the essential oils belong to the class of
chemical compounds called terpenoids which are produced from different
precursors like Isopentenyl pyrophosphate (IPP) and Dimethylallyl
pyrophosphate (DMAPP) during several metabolic pathways (Sangwan et al.,
2001). These are present either as mono terpenes, sesqui terpenes, di terpenes, tri
terpene and tetra terpene produced during pyruvate and mevalonate pathways
(Buchanan et al., 2000). Essential oil composition inside the plant depends on
developmental stages, agronomic practices, and post harvest procedures (Hay,
1993). Carvone is an important member of mono terpene family a prominent
constituent of spearmint, caravay, dill weed is an important compound for potato
sprout inhibition. Carvone biosynthesis in spearmint starts with the combination
of IPP and DMAPP to form geranyl diphosphate (GPP). Initially GPP is cyclized
to limonene which in turn hydroxylated to trans-carveol, which is eventually
oxidized to carvone (Bouwmeester et al., 1998). Phenylpropanoids are less
frequent in essential oils and act as natural defense mechanism against
microorganism, insects and animals (Sangwan et al., 2001). Phenyl alanine and
tyrosine are the main precursors which cause their biosynthesis during shikimate
pathway (Buchanan et al., 2000). The major phenyl propanoids found in certain
plant essential oils include eugenol, myristicin and methyl cinnamate (Sangwan et
al., 2001). Eugenol is the active component in clove oil being used for potato
sprout suppression. Phenylalanine along with NADPH cause the biosynthesis of
eugenol in the aromatic plants catalyzed through the enzyme eugenol synthase
(Koeduka et al., 2006).
43
In addition different other techniques have been employed to
prevent potato sprouting under storage. Rezaee et al. (2011) exposed potato
tuber cv. Agria with gamma irradiation on different dates during their post
harvest storage. He observed complete sprout inhibition by 50 Gy (Grays)
and 150 Gy at 8oC and 16oC temperature respectively. Saraiva et al. (2011)
reported sprout inhibition in potato tubers by pressure treatment of 100
Mpa for 5-10 min. Low pressure (30-50 Mpa) did not prevented potato
sprouting however found efficient in delaying sprout development.
Kyriacou et al. (2008) investigated impact of different time and
temperature variables regarding hot water treatments for sprout prevention
in potato. He concluded that short duration hot water treatment can prevent
potato sprouting and dehydration during subsequent storage. Rangana et al.
(1998) recommended hot water treatment at 57.5°C for 30 min to improve
storage stability in potatoes. Potatoes storage can successfully be carried
out at 8 or 18°C for 12 weeks without sprouting with no adverse effects on
the over all quality parameters. Shabana et al. (1987) studied the effectiveness
of different wax applications for sprout suppression and found reduced solanine
contents in treated potato during storage.
With the advent of safe food concept and environmental concerns
pertaining to the use of chemical sprout inhibitors like CIPC, IPC, MH the
need arised to develop integrated sprout management approach to ensure
potato storage with out the use of hazardous chemicals. The storage of
premium potato variety with the help of cheap sprout suppresents of natural
origin will facilitate the poor farmers for economic storage. In addition
44
development of potato crop free of such detrimental effect will also enable the
local farmers for “organic” potato storage which recieve top notch in the
international market
2.14 CHIP COATINGS
Potato chips are the oil rich (35-40%) products (Moreira et al., 1999) and
considered as preferred snack food world over due to its palatable taste and ease of
preparation. The high fat contents however of grave concern for the peoples
suffering from chronic heart diseases and obesity. Different techniques have been
employed to minimize the oil contents in the final products like, modification in
size and thickness (Gamble and Rice, 1988), pre drying (Pedreschi and Moyano,
2005), modification in frying techniques (Mehta and Swinburn, 2001) and frying
medium (Berry et al., 1999), frying temperature (Mellema, 2003) and potato chips
coatings (Williams and Mittal, 1999).
Application of different coating materials reduces oil uptake and improves
consumer preference for the fried products. The fat uptake in the fried products is
determined by two mechanisms i.e condensation effect and capillary effect
(Mellama, 2003) which are altered by the application of different coating materials.
Since the fat uptake by the chips is largely the function of its surface properties
thus coating is considered as promising route for its mitigation in finished
processed product. In addition, pre processing coating application on potato
products reported to mitigate likely acrylamide formation in the processed products
(Fiselier et al., 2004). Different types of coating materials are employed during
frying operations however the selections of proper coating material with desirable
45
barrier and mechanical properties are essential for the premium quality production.
These coating materials can be thin and invisible (Gennadios et al., 1997) or thick
like batter (Fiselier et al., 2004).
Albert and Mittal, (2002) studied the effect of different coating materials
like gelatin, gellan gum, methyl cellulose, pectin, sodium caseinate, soya protein
isolates, wheat protein, and found general reduction in fat uptake as compare to
control. Mallikarjunan et al. (1997) reported that the coating with cellular
derivatives cause the formation of protective layer on the surface eventually
decreases the fat uptake in the fried products. Garcia et al. (2002) evaluated the
surface application of cellulose derivatives in different formulations for the
reduction in oil uptake in fried products. He concluded that coating reduced the oil
uptake by 35-40% with appreciable retention of different sensorial attributes.
Garmakhany et al. (2008) studied the comparative effect of different hydrocolloids
(carboxy methyl cellulose, xanthan gum, guar gum) applications on the quality
attributes of potato chips. He revealed that CMC 1% application cause minimum
fat uptake and maximum color scores in the fried products.
Aloevera is tropical and subtropical plant widely known to its theraptic and
medicinal properties (Eshun and He, 2004). It is mucilage gel extracted from leaf
parenchymatic cell predominantly being used since long against cardio vascular
diseases, ulcer, gastro intestinal and renal disorders (Ni et al., 2004). Owing to its
antibiotic and anti inflammatory properties it has also been considered as remedy
against lethal diseases like AIDS and cancer (Renoylds and Dweck, 1999). The use
of aloevera gel has also been increasing in cosmetic industry (Aburjai and Natsheh,
2003) and known to carry antifungal activity (Saks and Burkai-Golan, 1995). In
46
addition it is increasingly being used as functional ingredient in food industries for
ice creams, beverages and desserts production (Moore et al., 1995). It is reported to
carry specific barrier properties and thus used as postharvest edible coating to
increase the shelf life of Cherries (Martinez-Romero et al., 2006) and table grapes
(Valverde et al., 2005).
Selection of aloe vera gel for chips coating in the present study has been
carried out as novel technique in processing. The application was required for the
development of plant based coating material i.e. HALAL (permissible food in
Islamic jurisprudence) to get reduced fat uptake in potato chips along with
appreciable retention of sensorial attributes. Such high quality processed product
would equally be the appreciated by the processor and consumer due to added
economic and health benfits.
2.15 ACRYLAMIDE
Toxic compounds found in thermally processed starchy foods are called as
Acrylamide (AA) (Svensson et al., 2003) and the International Agency for
Research on Cancer declared them to be animal carcinogen (Group 2A), possible
genotoxic carcinogen and neurotoxin to humans (IARC, 1994). The deep fried
starch rich foods like French fries, doughnuts, potato chips and extruded snacks are
rich source of these toxic compounds (Moreira et al., 1999).The presence of this
lethal compound in baked and fried starchy foods has created great concerns
regarding consumer`s food safety.
47
United States is the one of the biggest consumers of potato chips with an
over all consumption of around 1.2 billion pounds per year (USDA 2002).
Previously this consumption of potato chips was not considered as a health hazard,
however a recent study revealed that when starchy foods are subjected to high
temperature during a cooking a process of baking and frying, they release highly
toxic chemicals known as acrylamide, which become a part of the finished product
and present a serious threat to human well being (Kita et al., 2004). Desirable
commercial attributes of aroma, taste and appearance can only be achieved by the
process of browning, which results in caramelization and maillard-reactions
imparting the toxic AA in the finished product.
Several scientists proposed different techniques to mitigate acrylamide
formation in foods during processing. The critical test will however be to attain
significant acrylamide reduction in processed food with intact product sensorial
and nutritional attributes. The concentration of reducing sugars has been the prime
contributor of acrylamide formation during processing and determines the color of
fried products. Potato intended for roasting, frying or baking should contain less
than 1g/kg reducing sugar to mitigate likely acrylamide formation (Biedermann-
Brem et al., 2003). The use of different organic acids has been found very effective
in decreasing the acrylamide contents in the processed products. Low pH plays an
important role in reducing acrylamide formation and primarily being achieved in
different foods through organic acids like citric, acetic and lactic acid (Mestdagh et
al. 2007). Granda et al. (2004) reduced acrylamide formation in potato chips by
vacuum frying between 118oC and 140oC at 1333 Pa. The process minimized
acrylamide formation by 94% without conferring significant modifications in
48
sensorial parameters of processed potato. The use of different hydrocolloids
application during processing confers moisture barrier properties to the food
products. Fiselier et al. (2004) coated potato croquettes with blend of breadcrumbs
and egg before heating and found considerable reduction in acrylamide content
(280 to 50 parts per billion). Vattem and Shetty, (2003) also observed reduced
acrylamide formation (930 to 580 parts per billion) by coating the potato strips
with chickpea batter before deep-fat frying. Large variation in acrylamide contents
has been reported in different potato varieties used in processing operations In
general varieties having low reducing sugar and protein contents have been
associated with reduced acrylamide contents in finished products. Varieties like
Agria, Lady Rosetta, Lady Clair, Lady Jo, Jupitor, Saturna etc. grown under sandy
loam and clay soils are reported to produce less acrylamide contents in French fries
(De Wilde et al., 2006).
The available information on acrylamide formation so far emphasizes
common recommendation on healthy food intake. People should consume
balanced and antioxidants rich diet composed of fruit and vegetables as their major
food segment, and restrains the intake of thermally processed foods. There is
consensus on the health risk caused by the acrylamide hence it can easily be
concluded that if it is not possible to avoid these harmful compounds than there
level should be kept to as low as possible and a term used for the reduced
acrylamide is ALARA (as low as reasonably achievable), which is a globally
accepted principle when it comes to the formation of acrylamide in the food items.
49
Chapter 3
MATERIALS AND METHODS
3.1 PHASE-I
In the 1st Phase physico-chemical, functional and processing attributes of
ten commercial potatoes (Solanum tuberosum L.) were studied. These varieties
were harvested from Potato Research Institute, Sahiwal (Punjab-Pakistan) in
January 2009 and were immediately transferred to the Food Technology
Department, PMAS-Arid Agriculture University, Rawalpindi (Punjab-Pakistan)
where the trials were carried out. Six were yellow-white skinned namely, Agria
(AGR), Atlantic (ATL), Chipsona (CHI), Desi (DES), Hermes (HER) and Satellite
(SAT), four were reddish skinned Cardinal (CRD), Courage (COU), Desiree
(DESR) and Lady Rosetta (LR). These were chosen because of the recent increase
in their production and contribution to the processing industry in Pakistan. The
tubers were graded into homogenous lots of > 50 mm length, sorted for the
exclusion of damaged, diseased and sunburned tubers afterward placed between
15-20oC for suberization for one week.
3.2 PHASE-II
For the 2nd Phase of the study potato variety “Lady Rosetta” was harvested
from Potato Research Institute, Sahiwal (Punjab, Pakistan) in January, 2010. The
experimental material was shifted to the Post harvest Technology Laboratory of the
same University. Potatoes were washed, sorted and graded into homogenous lot
before subjecting to the different analytical trials. The selected tubers were cured
49
50
for one week at temperature between 15-20oC. The second phase is further divided
in to four experiments as described below:
3.2.1 Packaging Trial
Packaging trial of potato variety “Lady Rosetta” was carried out as a 1st
experiment of second phase of the study. Potatoes were packed in different
packaging materials of same size (30 cm × 40 cm) and perforations (10%)
procured from Ms. Multi packages Ltd. (Lahore, Pakistan). The set of treatments
included:
1. T1 = Control
2. T2 = Jute packaging (JP)
3. T3 = Nylon packaging (NP)
4. T4 = Poly propylene packaging (PPP)
5. T5 = Cotton packaging (CP)
6. T6 = Low Density Polyethylene packaging (LDPEP)
7. T7 = Medium Density Polyethylene Packaging (MDPEP)
8. T8 = High Density Polyethylene Packaging (HDPEP).
One Kg potato tubers were placed in each replication and 3 kg tubers were
maintained in each treatment for per day analysis. In total 30 Kg (Thirty packaging
per treatment) potatoes were placed in each treatment later subjected to different
physico-chemical and processing analysis at week and bi week intervals
respectively. All the packaged potatoes were stored at temperature and relative
humidity maintained around 25±2oC and 70±5%, respectively.
51
3.2.2 Light Trial
Light trail of potato variety Lady Rosetta was carried out as 2nd experiment
of the second phase of the study. The potatoes were placed under different light
sources in specially designed cabinets. The trial was divided into following set of
treatments:
1. T1 = Blue light (BL)
2. T2 = Fluorescent light (FL)
3. T3 = Green light (GL)
4. T4 = Mercury Light (ML)
5. T5 = Red light (RL)
6. T6 = Dark (D)
Potatoes were placed under lamp of 20 W of different light sources
maintained at a distance of 1 m during storage except in T6. All the tubers were
bared to specific light and rotated at 24 hours interval to ensure maximum skin
exposure. 1 kg potato tubers were placed in each replication and 3 kg tubers were
maintained in each treatment for per day analysis. In total 30 Kg potatoes were left
in each treatment and were subsequently subjected to different physico-chemical
and processing analysis at three days and a week interval respectively. All the
potatoes were stored at temperature and relative humidity maintained around
25±2oC and 70±5% respectively.
3.2.3 Temperature Trial
Potato variety Lady Rosetta was placed under different temperature
regimes with relative humidity maintained at 70±5% to conduct 3rd experiment of
52
second phase of the study. The potatoes were placed under three temperature
regimes:
1. T1 = 5 ±1oC
2. T2 = 15 ±1oC
3. T3 = 25 ±1oC.
One kg potato tubers were placed in each replication and 3 kg tubers were
maintained in each treatment for per day analysis. In total 30 Kg potatoes placed in
each treatment and were subjected to different physico-chemical and processing
analysis at bi week intervals.
3.2.4 Sprouting Trial
Potato variety Lady Rosetta was subjected to different sprout controls to
conduct 4rth experiment of second phase of the study. Potatoes were subjected to
different treatments as under:
1. T1 = Control
2. T2 = Hot Water Treatment (55 ±2oC for 30 minutes)
3. T3 = Spearmint Oil (1%)
4. T4 = Clove Oil (1%)
5. T5 = CIPC (100 ppm)
Hot water treatment was carried out in water bath maintained at specific
temperature and time once before the start of storage. Spear mint and Clove oils of
100% purity were supplied by Ms. Shah Traders (Karachi, Pakistan). 1%
emulsions each of spear mint and clove oils were prepared in distilled water with
0.05% Tween 80 used as an emulsifier. Tubers were dipped in emulsion for 20
53
seconds ensuring the entire tuber surface was coated. CIPC was procured from Ms.
United Phosphorus Limited (Gujrat, India) and applied once as thermo aerosol in
the storage chambers at specified concentration (100 ppm).
One kg potato tubers were placed in each replication and 3 kg tubers were
maintained in each treatment for per day analysis. In total 30 Kg potatoes were left
in each treatment during storage (Temp. 25±2oC, R.H. 70±5%) afterward subjected
to different physico-chemical and processing analysis at nine days interval.
3.3 PHASE-III
For the 3rd phase of the study potato variety “Lady Rosetta” was harvested
from Potato Research Institute, Sahiwal (Punjab, Pakistan) in January 2011. The
experimental material was shifted to the Post harvest Technology Lab. Food
Technology Department, PMAS-Arid Agriculture University, Rawalpindi.
Potatoes were washed, sorted and graded into homogenous lot before subjecting to
the different analytical trials. The selected tubers were cured for one week at
temperature between 15-20oC.
The results identified in the 1st and 2nd phase were evaluated in combination
in third phase to assess different quality attributes along with the eventual post
harvest storage life in potato tubers. The potato variety lady Rosetta was given hot
water treatment (55±2oC for 15 minutes) followed by Clove Oil application (1%).
Tubers were packed in Polypropylene packaging and than stored at 10±1oC
temperature and 70±5% R.H. The potatoes were divided into two homogenous lots
for analysis:
1. T1 = Control
2. T2 = Integrated Treatment
54
One kg potato tubers were placed in each replication and 3 kg tubers were
maintained in each treatment for per day analysis. In total 30 Kg potatoes were left
in each treatment which were subjected to different physico-chemical and
processing analysis at twenty and thirty days intervals respectively.
3.3.1 Potato Chip Coating
In the third phase of study potato processing was carried out only in the
tuber placed in T2 (integrated treatment). Pre processing potato chip coating was
carried out in different levels of Aloe vera gel followed by subsequent frying at
180-185oC temperature. Aloe vera gel was extracted from freshly harvested aloe
vera leaves and blanched at 70oC for 10 minutes. Aloe vera gel was prepared in
three different formulations each with 1% sorbitol (Sigma-Aldrich, USA) added as
plasticizer along with distilled water as under:
1. T1= Control
2. T2 = Aloe vera (10%)
3. T3 = Aloe vera (20%)
4. T4 = Aloe vera (30%)
The potato chips were dipped in prepared formulations for 5 minutes,
allowed to drip off and dried before frying. The frying was carried out at thirty
days interval in potato stored under intergrated treatment.
Different physico-chemical, functional and processing attributes in potato
tubers during different phases (1, 2 and 3) of the present study were performed
55
according to standard methods described as under. All the results were expressed
on dry weight basis in phase no.1 in order to record appropriate comparison
between the selected varieties.
3.4 PHYSICO-CHEMICAL AND FUNCTIONAL ANALYSIS OF
POTATO
3.4.1 Physical Analysis
3.4.1.1 Size
Potato size in terms of linear dimension (L) was determined by digital (0-
150mm, China) with precision of +0.01 mm.
3.4.1.2 Goemetric mean diameter
Geometric Mean Diameter (Dg) was determined by the multiple of Length
(L), Width (W) and Thickness (T) of potato as described in the equation given
below
Dg = (LWT) 0.333
3.4.1.3 Sphericity
Equation described by Ahmadi et al. (2008) was employed for the
determination of tuber Sphericity as under:
Ф= (Dg/ L) ×100
Where as Dg = Geometric Mean Diameter, L= Length
3.4.1.4 Surface area
Equation reported by Baryeh, (2001) was employed for the estimation of
surface area in potato tubers as under:
56
S = π Dg 2
Where, Dg = Geometric Mean Diameter.
3.4.1.5 Tuber counts
Individual tuber counts (TC) in different varieties were estimated manually
per 25 Kg packaging as:
Tuber counts = (TC)/25 Kg.
3.4.1.6 Firmness
Potato tuber Firmness was determined by fruit Firmness Tester model
(Wagner FT-327) euipped with 11mm plunger. Results quantified were converted
in to Kilopascals (Kpa).
3.4.1.7 Specific gravity
Tuber Specific gravity was measured by the estimation of tuber weight in
air and tuber weight in water. The specific gravity was determined by the
following equation as described by Gould, (1995).
Weight in air Specific Gravity =
Weight in air – Weight in water
3.4.1.8 Total soluble solids
Total Soluble Solid (TSS as oBrix) was estimated in the homogenized
potato tuber in each varietals sample by using a Digital refractometer (Model PAL-
III, ATAGO-Japan) as reported by AOAC (1990) method no. 932.12.
Standardization of Instrument was carried out by using distilled water at 25±1oC
temperature.
57
3.4.1.9 pH
The pH values were recorded by using a pH-meter (Inolab. WTW Series,
Germany) as illustrated in AOAC (1990) method no. 981.12. The instrument was
carefully calibrated with Buffers 4, 7 and 10. The reading was recorded by the
direct insertion of electrode in the homogenized sample taken in the beaker.
3.4.1.10 Sprouting
Sprouting (SPRT) percentages in potato tubers (sprout length > 3mm)
were calculated by the equation described by Ranganna et al. (1998).
No. of eyes sprouted Sprouting (%) = × 100. Total no. of eyes
3.4.1.11 Weight loss
The weight loss (%) in different experiments at specified storage
interval was determined by weighing the samples with digital balance (OHAUS,
Model TS4KD Florham Park, NJ, USA) and reported as percent loss in sample
weight based on its initial weight.
Initial weight - Final weight Weight loss (%) = ×100
Initial weight
3.4.2 Chemical Analysis
3.4.2.1 Dry matter
Dry matter (DM) was determined by Oven Drying method at 102oC till
constant weight is achieved as described in AOAC (1990) method no. 934.06. The
calculations were carried out as under:
58
Weight of Fresh sample - Weight of Dry sample Dry Matter (%) = × 100
Weight of Fresh sample
3.4.2.2 Starch
Starch estimation was carried out by making the tuber sugar free by the
repeated extraction with 80% iso-propanol. Tubers were dried at 70oC and than
starch were hydrolyzed by 60% perchloric acid. The glucose was estimated
spectrophotometerically by using anthrone reagent as described by Kumar et al.
(2005).
3.4.2.3 Protein
Crude protein estimation was carried out by multiplying the total nitrogen
contents with conversion factor 6.25 using the Kjeldhal apparatus as described by
AOAC (1990) method no. 920.10. 5grams of homogenized sample was digested
with the addition of 1 gram copper sulphate, 10 grams potassium sulphate and 30
milliliter sulphuric acid in the digestion flask. The procedure was followed by
continuous heating till color less matter was obtained. Consequential material was
diluted with distilled water followed by distillation in the presence of 10 milliliter
sodium hydroxide (40% solution) in the distillation apparatus. The liberated
ammonia was trapped in 4% boric acid solution containing methyl red as indicator.
Distillate obtained was titrated with sulphuric acid (0.1 N solutions) to attain
golden brown end point.
Nitrogen (%) was estimated by the equation described below:
1.4 (V2-V1) × Dilution factor × Normality of HCl N (%) =
Sample weight
59
Protein (%) was estimated as the multiple of Nitrogen (%) and Conversion factor
(6.25)
3.4.2.3 Fat
Crude fat was determined according to the AOAC (1990) method no.
983.23. Dried 10g sample placed in thimble was extracted with hexane (B.P 40-
60oC) taken as solvent in pre weighed soxhlet flask. The solvent was recovered
after the completion of extraction process and fat containing flask was dried in
Oven till constant weight. The crude fat contents were gravimetrically determined
by the following equation.
Weight of flask+ fat - Weight of empty flask Fat Contents (%) = × 100
Weight of sample
3.4.2.4 Sugar
Lane and Eynon titration method using Fehling’s solution was employed
for the estimation of Reducing sugar (RS), non reducing sugar (NRS) and total
sugars (TS) contents as reported in AOAC (1990) method no. 925.35. Ten grams
sample was diluted with 100 ml warm water, stirred thoroughly to dissolve all
suspended particles subsequently filtered in 250 ml volumetric flask. 100 ml of
prepared solution was transfer in to conical flask along with 10 ml of diluted HCl
and boiled for 5 minutes. The resultant solution was cooled and neutralized with
10% NaOH and made up to volume in 250 ml volumetric flask. The solution was
titrated against Fehling`s solution and reading were recorded as under:
4.95 (Factor) × 250 (Dilution) ×2.5 Total Sugar (%) =
Weight of sample × Titre× 10
60
4.95 (Factor) × 250 (Dilution) Reducing Sugar (%) =
Weight of sample × Titre × 10
Non Reducing Sugar (%) = Total Sugar - Non Reducing Sugar
3.4.2.5 Glucose
Glucose estimation was carried out by Glucose test strips imported from
Snack Food Association, (Arlington Virginia USA). The color change was
correlated with the color chart and the values were expressed in percentage (%).
The tests were conducted in triplicate.
3.4.2.6 Fiber
Crude fiber estimation was carried out according to AOAC (1999) method
no.920.86. 5g dried fat free sample was digested with 1.25% sulphuric acid
followed by 1.25% NaOH solutions. The residue obtained filtered, washed and
ignited in muffle furnace at 550oC till the formation of white ash.
Crude fibre estimation was carried by the following equation:
(c-b) – (d-b) Crude Fibre (%) = × 100
(a) Where; a = Sample weight, b = crucible weight, c= sample weight before ignition
d= sample weight after ignition.
3.4.2.7 Ash contents
Ash content was determined AOAC method no. 940.26 (1990). 5g sample
was directly incinerated in the muffle furnace at 550oC till grayish white residue
was obtained. The ash content was estimated as:
61
Weight of Ashed sample Ash contents (%) = × 100
Weight of sample
3.4.2.8 Mineral composition
Mineral estimation in potato tubers was carried out according to AOAC
(1999) method no. 923-07 with some modifications. Five grams sample was
digested at 180- 200oC temperature in the presence of nitric acid and perchloric
acid in the ratio of 7 milliliters and 3 milliliters respectively to acquire transparent
clear contents. The received transparent contents were diluted with bidistilled
water in 100 ml flask. Mineral contents like iron, magnesium, calcium in potato
tubers were estimated by Atomic Absorption Spectrophotometer (GBC-932
Australlia) against their standard curves of known concentrations. Estimations of
sodium and potassium were determined by Flame Photometer (Model PFP 7
Jenway, England) whereas phosphorus detection was carried out in
Spectrophotometer (CE-2021, 2000 series CECIL Instruments Cambridge,
England).
3.4.3 Functional Assays
3.4.3.1 Ascorbic acid
Ascorbic acid (AA) estimation was carried out by titrametric method by
employing 2, 6, di-chlorophenol indophenol dye (redox dye) as explained in
AOAC (1990) method no. 967.21. 10 g representative sample was taken in beaker
and made up to volume with 100 ml 3% Phosphoric acid and filtered. 10 ml of
filtrate was titrated with the standard dye solution till pink end point. The ascorbic
acid contents were quantified as under:
62
Dye factor × Titration × Volume made up Ascorbic acid (mg/100g) = × 100
Weight of sample × Volume of filtrate
Dye standardization: Five milliliters of standard ascorbic acid solution was diluted
with five milliliter of metaphosphoric acid (3%) and titrated with dye
solution till pink color endures for ten seconds. Dye factor was estimated (mg
ascorbic acid/ ml of dye) as:
Dye Factor (D.F) = 0.5/ titration.
3.4.3.2 Total glycoalkaloids
The Total glycoalkaloids (TGA) determination was carried out by the
method described by Grunenfelder et al. (2006). Ground lyophilized potato tissue
(500 mg) was extracted in 10 ml of 80% ethanol at 85-90oC for 25 minutes. The
extract were filtered and reduced to 3-5ml on rotary evaporator at 50oC. Each
extract was rinsed twice with 3ml of 10% (v/v) Acetic acid and than centrifuged at
10,000g for 30 minutes at 10oC. The pH of the supernatants was adjusted at 9.0
with NH4OH. The extract was refluxed at 70oC for 25 minutes followed by
overnight storage at 4oC temperature. The extract were similarly centrifuged as
earlier, after discarding the supernatants the resulting pellets were dissolved in 0.5
ml of 7%( v/v) phosphoric acid and stored at -20oC. The Total Glycoalkaloids were
estimated by adding 200µL of extract in 1 ml of 0.03% (w/v) in concentrated
phosphoric acid. The contents were allowed to settle for 20 minutes and
absorbance was measured at 600nm. TGA concentrations were quantified based on
63
α-solanine (Sigma-Aldrich) standard curve using a CE-2021, Spectrophotometer
(CECIL Instruments Cambridge, England) and expressed as mg TGA/100g d.w.
3.4.3.3 Chlorophyll
Chlorophyll (CHL) extraction from different tuber samples was carried out
by acetone and subsequent quantification was done in spectrophotometer as
illustrated by Percival, (1999). Five grams representative (selected from each side
of potato tuber) lyophilized tissues were ground to a fine powder with the help of
mortar and pestle. Sample was transferred to test tubes followed by extraction with
10 milliliter of acetone. The extract was vortexed than stored at 4oC for 24-72
hours. After storage chilled extracts were again vortexed and centrifuged for 15
minutes at around 2,500 g. The supernatant was collected for chlorophyll
determination.
Chlorophyll content was measured in 1.00-cm cuvettes at A647 and A664.5
using Spectrophotometer (CE-2021, 2000 series CECIL Instruments Cambridge,
England).
Total chlorophyll concentrations were expressed as mg/100g d.w from the
following equation:
Total Chl = 17.90 (A647) + 8.08 (A664.5)
3.4.3.4 Total phenolic contents
Total phenolic contents (TPC) in terms of Gallic acid Equivalent (GAE)
were carried out by Folin–Ciocalteu (FC) assay as explained by Lachmann et al.
(2008) with few modifications. Tubers randomly selected were freeze dried and
64
than extracted thrice with 80 % ethanol to get representative plant extract. 2 gm
extract was quantitatively converted into 100 ml volumetric flask and adjusted with
80% ethanol. In 5 ml of the sample slightly diluted with distilled water, 2.5 ml of
FC and 7.5 ml of 20% solution of sodium carbonate were added. Contents were
allowed to settle for 2 hours and absorbance was measured at 765 nm using a CE-
2021, Spectrophotometer (CECIL Instruments Cambridge, England). Total
phenolic contents were quantified by standard calibration curve derived from the
absorbance of known Gallic acid concentration (10-100 ppm). Results were
articulated as mg Gallic Acid Equivalents (GAE) per 100g d.w.
3.4.3.5 Radical scavenging activity (RSA)
Antioxidant activity was measured as radical scavenging activity (RSA)
using method described by Singh and Rajini, (2004) that involves electron transfer
reaction based assay by employing free radical 2, 2-diphenyl-1-picrylhydrazyl
(DPPH). Five mg of freez dried potato extract was incubated with 1.5 ml of DPPH
solution (0.1mM in 95% Ethanol). The reaction mixture was properly shaken and
allowed to stand for 20 minutes under ambient temperature. Absorbance of the
resultant mixture was determined at 517nm against blank. The radical scavenging
activity was determined as decrease in the absorbance of DPPH using the
following equation.
Asample 517 nm Scavanging effect (%) = 1 - x 100
AControl 517nm
65
3.4.3.6 Enzyme estimation
3.4.3.6.1Extraction and protein estimation:
Enzyme extraction was carried out by the method described by
Yemenicioglu, (2002) with some modifications. Washed, peeled and diced
potatoes were placed under -20oC before homogenate preparation. 200 grams
frozen potato was homogenized with 300 ml acetone and 1gram
polyvinylpolypyrrolidone (PVPP) in waring blender. The resultant mixture was
homogenized for 2 minutes subsequently filtered through whatman No.1. Acetone
powder preparation was carried out by repeated extraction and evaporation. The
extraction mixture was prepared by mixing 0.4 g PVPP, 2g acetone powder and 50
ml of cold 8.8% Sodium chloride solution. Extraction was completed at 4oC
temperature 3 hours under magnetic stirrer. The extract was filtered, centrifuged at
11000g for 20 minutes and subsequently stored at -20oC prior to enzyme
estimations.
Protein estimation was carried out by Lowry method using bovine serum
albumin (BSA) as standard. Protein standards of crude and partially purified
extracts were prepared in 8.8% NaCl solution and deionized water respectively. All
the assays were carried out in triplicate. The enzyme activity was calculated as
U/g fresh weight, in spectrophotometric assay 1 U was defined as 0.001 change in
absorbance per minute per ml of enzyme extract.
3.4.3.6.2 Polyphenol oxidase (PPO) assay:
Poly phenol Oxidase (PPO) activity was determined by the method as
described by Yemenicioglu, (2002). The reaction mixture contained 2ml 0.01M
66
sodium phosphate buffer (pH 7.0), 0.2 ml of 0.25 M catechol and 0.3 ml enzyme
extract to the total volume of 2.5 ml. The optical density (OD) of the reaction
mixture was determined spectrophotometerically at 420 nm. PPO activity was
calculated by the change in OD over a period of thirty seconds and expressed as
U/g fresh weight.
3.4.3.6.3 Per oxidase (POD) assay:
Peroxidase estimation was carried out as reported by Abbasi et al. (1998).
Reaction mixture consisted of 2.1 ml, 15mM NaKPO4 buffer (pH 6.0), 0.3 ml
1mM H2O2, 0.3 ml 0.1 mM guaiacol and 0.3 ml enzyme extract to the total volume
of 3 ml. The optical Density (O.D) of the reaction mixture was determined
spectrophotometericaly at 470 nm. POD activity was estimated by the change in
O.D due to guaiacol oxidation over thirty seconds time and expressed as U/100g
fresh weight.
3.4.4 Potato Chips Evaluation
The potato tubers during different experiments were processed into potato
chips. Peeled tubers were sliced (1.2-1.5 mm thick) and blanched in 1.5% NaCl
solution at 85oC for 2 minutes. After pre drying the chips were fried in electric
fryer at 180- 185oC temperatures for 3 minutes using palm oil. The fried chip were
cooled and placed in Dry Oven at 105oC till constant weight for moisture contents
(MC) estimation The fat absorption (FAB) in different chip samples were
determined by Soxhlet Extraction apparatus as described by AOAC (1990) method
no. 983.23. The estimation of Glycoalkaloids (TGA) as solanine in potato chips
67
was carried out by the same method as described above. Twenty five students
including the faculty members of Department of Food Technology who were the
habitual consumers of the potato chips selected as judge for the sensory evaluation.
The judges were requested to record their degree of preferences for Crispiness
(CRP), Flavor (FLV) and Taste (TAS) according to the five point hedonic scale as
described by Kita (2002). The Color (COL) of the chips was correlated with
British Potato Council (BPC) Frying color chart and the values were expressed as
approximate L-values.
3.5 STATISTICAL ANALYSIS
Results obtained in first phase of the study were subjected to statistical
analysis by considering the varieties as variation source, using one-way analysis of
variance (ANOVA). Statistical differences with P-values under 0.05 were
considered significant. Date obtained in second and third phases were statistically
analyzed by two factor factorial in Completely Randomized Design (CRD) using
M-StatC Statistical software as described by Steel et al. (1997).
68
Chapter 4
RESULTS AND DISCUSSION
4.1 PHYSICO-CHEMICAL, FUNCTIONAL AND PROCESSING ATTRIBUTES OF POTATO VARIETIES
In the 1st phase of the present study ten commercial potato varieties namely,
Agria, Atlantic, Cardinal, Courage, Chipsona, Desiree, Desi, Hermes, Lady Rosetta
and Satellite were studied for their physical, chemical and functional attributes,
with special reference to their potential in chip processing.
4.1.1 Physical Attributes of Potato Varieties.
Table-1a summarizes the mean values obtained for each of the varietals
physical attributes like, Size, Geometric Mean Diameter (GMD), Sphericity,
Surface Area, Tubercounts/25Kg, Firmness, Specific Gravity, TSS, pH and
Sprouting Potential. The results of one way Anova to compare the means for
different varieties are also included. The significant differences were recorded
between varieties for their physical parameters which were correlated (Table-1b).
Hermes yielded maximum tuber size (94.25 mm) followed by Desi (91.20 mm)
and Desiree (85.41 mm) and were inversely related to the tuber counts/25Kg
packaging (R= -0.967). Hermes exhibited maximum surface area (18010.93 mm2)
followed by Courage (16067.80 mm2) and Lady Rosetta (15924.29 mm2). Variety
Atlantic experienced maximum sphericity (95.38%) followed by Lady Rosetta
(94.29%). The parameters discussed above have essential role in defining the
processing yield of different varieties as described in British Quality Chip Charter
by British Potato Council (BPC). The sugar contents were significantly higher
in small sized tubers (Misra and Chand, 1990) thus the tubers < 50 mm sizes
68
69
Table 1a Physical attributes of potato varieties. Variety Size
(mm)
GMD (mm)
Sphericity (%)
Surface area (mm2)
TC/25 kg Firmness (Kpa)
Specific Gravity
TSS (oBrix)
pH SPRT (%)
AGR 76.27 ± 2.95 d
66.93 ± 1.53 d
87.75 ± 2.57 b
14075.25 ± 9.71 e
160.00 ± 1.12 c
799.00 ± 7.88 g
1.081±0.09 f
5.44 ± 1.18 h
6.17 ± 1.12 e
47.50 ±2.12 g
ATL 64.99 ± 1.73 f
61.99 ± 2.17 e
95.38 ± 2.38 a
12077.79 ± 8.81 g
186.30 ± 0.98 a
925.00 ± 5.19 b
1.092 ± 0.06 b
5.54 ± 1.12 g
6.21 ± 1.16 c
42.33 ±1.36 h
CAR 83.30 ± 2.30 c
66.51 ± 1.15 d
79.84 ± 3.19 d
13903.31 ± 7.03f
155.00 ± 1.15 d
775.00 ± 4.04 h
1.074 ± 0.03 g
5.73 ± 1.17 d
6.15 ± 1.29 f
59.33 ±1.54 c
COU 78.43 ± 3.88 d
71.50 ± 2.28 b
91.16 ± 3.33 ab
16067.80 ± 8.31 b
154.30 ± 0.81 d
885.00 ± 5.48 c
1.090 ± 0.09 bc
5.69 ± 1.11 e
6.27 ± 1.16 a
53.75 ±2.15 e
CHI 68.53 ± 2.96 e
58.81 ± 1.47 f
85.81 ± 1.64 bc
14029.32 ±10.53 ef
166.00 ± 0.77 b
883.00 ± 3.64 c
1.089 ± 0.11 c
5.63 ± 1.36 f
6.17 ± 1.17 e
50.00 ±1.99 f
DESR 85.41 ± 2.37 c
68.31 ± 1.11 c
79.97 ± 2.17 d
14666.04 ± 9.48 d
150.30 ± 0.89 e
760.00 ± 5.19 j
1.070 ± 0.08 h
5.93 ± 1.15 a
6.27 ± 1.36 a
63.00 ±2.45 b
DESI 91.20 ± 4.15 b
70.92 ± 3.57 b
77.76 ± 3.81 de
15808.17 ± 13.72 c
131.00 ± 0.92 f
845.00 ± 8.77 e
1.086 ± 0.07 d
5.88 ± 1.39 b
6.25 ± 1.12 b
90.66 ±3.15 a
HER 94.25 ± 3.57 a
75.70 ± 2.17 a
80.31 ± 2.28 d
18010.93± 11.88 a
125.70 ± 1.20 g
829.00 ± 9.73 f
1.084 ± 0.04 de
5.62 ± 1.19 f
6.13 ± 1.11 g
36.00 ±1.27 i
LR 75.49 ± 2.87 d
71.18 ± 2.23 b
94.29 ± 3.37 a
15924.29 ± 9.43 b
165.70 ± 0.33 b
948.00 ± 6.92 a
1.102 ± 0.02 a
5.55 ± 1.49 g
6.18 ± 1.09 de
46.25 ±1.96 g
SAT 64.67 ± 1.81 f
54.50 ± 2.57 g
84.27 ± 2.47 c
9335.49 ± 3.56 h
185.30 ± 0.88 a
862.00± 4.61 d
1.083 ± 0.09b e
5.83 ± 1.20 c
6.27 ± 1.12 a
56.67 ±1.66 d
Dissimilar letters with in the column indicated significant difference (p< 0.05)
Value ± corresponds to the standard error
AGR (Agria), ATL (Atlantic), CAR (Cardinal), COU (Courage), CHI (Chipsona), DESR (Desiree), DESI (Desi), HER (Hermes), LR ( Lady Rosetta), SAT (Satellite)
GMD (Geometric Mean Diameter), TSS (Total Soluble Solids), SPRT (Sprouting Potential)
70
Table 1b Correlation between physical attributes
Size
GMD
Sphericity
Surface
area TC/25 kg
Firmness
Specific Gravity
TSS
pH SPRT
Size 1
GMD 0.831 1
Sphericity -0.669 -0.146 1
Surface area 0.784 0.925 -0.168 1
TC/25 kg -0.967 -0.804 0.651 -0.836 1
Firmness -0.531 -0.140 0.778 -0.069 0.451 1
Specific gravity -0.363 0.061 0.738 0.138 0.267 0.959 1
TSS 0.074 -0.277 -0.511 -0.092 -0.111 -0.328 -0.434 1
pH -0.187 -0.248 -0.003 -0.374 0.222 0.035 -0.110 0.169 1
SPRT 0.335 0.026 -0.553 -0.027 -0.319 -0.290 -0.283 0.437 0.537 1
71
were eliminated during the frying process. Tubers of Lady Rosetta followed by
Atlantic attained maximum Specific gravity (Table1a) and were significantly
correlated (R=0.979) with their Firmness (Table-1b). Cardinal and Desiree were
amongst the varieties with low specific gravity values. Difference between the
varieties on the basis of their specific gravity has also been reported by previous
researchers (Kumar et al., 2005). The maximum TSS was determined in Desiree
(5.930 oBrix) followed by Desi (5.880 oBrix). A narrow range in the pH values (6.12-
6.65) was observed in different tested varieties with non significant difference was
recorded between Courage, Desiree and Satellite. Varieties like Lady Rosetta and
Chipsona also exhibited non significant difference (P<0.05) in their pH values. The
minimal variations between the pH in different varieties were also accounted by
Gomez et al. (1997). At ambient storage (temp. 25±2 oC & R.H 60 ±5 %) for 60 Days,
Desi showed maximum sprouting percentage (90.66%) followed by Desiree (63.0%)
and Satellite (59.33%), in contrast longer dormancy and minimum sprouting was
experienced in Hermes (36.00%) and Atlantic (42.33%) (Table-1a).
4.1.2 Proximate Analysis of Potato varieties
Expressing proximate composition on dry weight basis (Table 2a) Lady
Rosetta produced the tubers with maximum Dry Matter (25.90%) and Starch contents
(77.39%) while lowest Dry Matter (21.24%) and Starch Contents (72.14%) were
estimated in Desiree. Highly Significant correlation (R= 0.986) was recorded between
these two quality parameters in all tested varieties (Table 2b) which confirmed the
previous findings by Casanas et al. (2002). A close range was estimated in the fat
contents (0.803 % to 1.293%) with maximum observed in Desi and minimum in Lady
72
Table 2a Proximate analysis of potato varieties (d.w basis).
Variety DM % Starch (g/100g)
Protein (g/100g)
Fat (g/100g)
Total Sugar (%)
Reducing Sugar (%)
N. R. S (%)
Fibre (g/100g)
Ash (%)
AGR 22.91 ± 1.22 g
74.42 ± 2.30 e
11.86 ± 1.27 b
0.970 ± 0.012 c
0.810 ± 0.017 h
0.110 ± 0.023 h
0.700 ± 0.012 h
7.24 ± 0.41 d
3.300 ± 0.581 bc
ATL 24.99 ± 2.91 b
76.69 ± 2.67 b
10.89 ± 2.39 d
1.000 ± 0.085 c
1.170 ± 0.058 f
0.320 ± 0.017 fg
0.850 ± 0.023 g
7.44 ± 0.61 c
1.897 ± 0.292 h
CAR 22.35 ± 0.95 h
73.62 ± 2.03 f
11.43 ± 2.07 c
0.970 ± 0.017 c
1.940 ± 0.023 c
0.450 ± 0.058 cd
1.290 ± 0.012 d
7.67 ± 0.40 b
3.250 ± 0.179 c
COU 24.75 ± 2.60 cd
76.52 ± 2.50 b
09.93 ± 2.35 f
0.810 ± 0.012 d
1.380 ± 0.017 e
0.400 ± 0.029 ef
0.980 ± 0.006 e
7.57 ± 0.52 bc
2.820 ± 0.581 f
CHI 24.45 ± 2.95 d
75.71 ± 1.95 c
11.00 ± 2.93 d
1.015 ± 0.011 c
1.385 ± 0.058 e
0.430 ± 0.058 de
0.960 ± 0.029 f
7.71 ± 0.55 b
2.889 ± 0.239 e
DESR 21.24 ± 3.81 I
72.14 ± 2.32 g
13.29 ± 2.91 a
1.275 ± 0.046 a
2.400 ± 0.058 b
0.570 ± 0.040 c
1.820 ± 0.040 a
6.75 ± 0.14 f
3.580 ± 0.115 a
DESI 23.89 ± 1.29 ef
75.45 ± 1.73 d
09.88 ± 1.28 f
1.293 ± 0.030 a
2.590 ± 0.035 a
0.900 ± 0.055 a
1.690 ± 0.058 b
7.83 ± 0.58 a
1.990 ± 0.237 h
HER 23.35 ± 5.87 f
75.36 ± 1.75 d
11.81 ± 2.33 b
0.997 ± 0.013 c
1.555 ± 0.035 d
0.383 ± 0.015 ef
1.170 ± 0.017 e
6.43 ± 0.75 g
3.107 ± 0.292 de
LR 25.90 ± 4.82 a
77.39 ± 1.32 a
10.50 ± 1.20 e
0.803 ± 0.026 d
0.935 ± 0.023 g
0.220 ± 0.012 gh
0.710 ± 0.023h
7.19 ± 0.58 d
2.560 ± 0.351g
SAT 22.82 ± 1.23 g
74.15 ± 1.92 f
11.95 ± 1.39 b
1.252 ± 0.015 b
2.250 ± 0.115 b
0.700 ± 0.029 b
1.550 ± 0.029c
6.94 ± 0.11 e
2.999 ± 0.186 e
Dissimilar letters with in the column indicated significant difference (p< 0.05)
Value ± corresponds to the standard error
d.w: Results expressed on dry weight basis
DM (Dry Matter), NRS (Non Reducing Sugars)
73
Table 2b Correlation between proximate components
DM Starch Protein Fat
Total
Reducing Sugar
N. R. S Fibre
Ash
Total
minerals
DM 1
Starch 0.986 1
Protein -0.803 -0.812 1
Fat -0.620 -0.634 0.421 1
Total sugar -0.589 -0.595 0.220 0.840 1
Reducing sugar -0.312 -0.317 -0.070 0.797 0.935 1
N.R.S -0.676 -0.680 0.365 0.863 0.983 0.875 1
Fibre 0.376 0.314 -0.695 -0.152 -0.030 0.150 -0.172 1
Ash -0.714 -0.717 0.748 0.031 0.067 -0.212 0.179 -0.488 1
Total mineral -0.472 -0.448 0.538 -0.199 -0.106 -0.338 -0.011 -0.528 0.898 1
74
Table 3 Mineral composition of potato varieties.
Variety Na (mg/ 100g)
K (mg/ 100g)
Fe (mg/ 100g)
Ca (mg/ 100g)
P (mg/ 100g)
Mg (mg/ 100g)
Total minerals (mg/ 100g)
AGR 6.83 ±0.15h 466.00 ±9.66b 1.760 ±0.12d 18.03 ±2.8a 63.83 ±2.61b 21.00 ±1.86g 577.50 ±16.20 a
ATL 9.55 ±0.29a 347.30 ±7.66i 2.277 ±0.19a 16.58±1.45c 40.67 ±2.14i 25.00±1.57cd 441.36±12.30 h
CAR 7.37 ±0.15f 460.10±6.45c 1.680±0.10ef 17.75±1.44ab 55.17±3.20e 27.67 ±1.72a 569.75±12.06 c
COU 7.42 ±0.15f 437.80 ±5.15e 1.823 ±0.18c 14.32 ±1.30d 51.43 ±4.56f 24.85±1.16 d 537.64±11.64 e
CHI 8.33 ± 0.14e 382.00 ±4.73h 2.143 ±0.27b 12.80 ±0.58g 42.33 ± 2.41h 27.73 ±1.12a 475.30±15.13 g
DESR 7.15 ±0.29g 482.00±8.07a 2.193 ±0.36b 13.20 ±0.98f 45.67 ±3.14g 24.30±1.06 e 574.55±13.92 b
DESI 8.55 ±0.29d 434.10 ±11.18f 1.450 ±0.12g 13.63 ±1.69e 57.00 ±2.57d 26.00 ±1.28b 540.73±9.25 e
HER 8.73 ±0.21c 453.50 ±7.85d 1.627 ±0.15f 17.45 ±1.73b 62.00 ±3.57c 25.53±1.06 c 568.80±13.57 c
LR 9.27 ±0.15b 426.00 ±11.52g 1.843 ±0.18c 16.90 ±1.45 c 71.33 ±5.14a 23.47 ±2.14f 548.85±18.58 d
SAT 6.69 ±0.55h 451.90 ±7.66d 1.707±0.29de 12.70 ±1.15g 36.17 ±1.14j 18.47 ±1.14h 527.62±10.93 f
Dissimilar letters with in the column indicated significant difference (p< 0.05)
Value ± corresponds to the standard error
Na (Sodium), K (Potassium), Fe (Iron), Ca (Calcium), P (Phosphorus), Mg (Magnesium).
75
Rosetta. Proximate analysis revealed that mean protein contents in potato varieties
were significantly different as also been mentioned by Casanas et al. (2009). Desiree
attained maximum Protein contents (13.29 %) while Desi was amongst the variety
with minimum (9.88%). Evaluation of total Sugar of potato varieties indicated that
Agria attained the least Sugar contents (0.810 %) followed by Lady Rosetta (0.935 %).
Reducing sugars and protein contents in the tuber varieties at elevated temperature
caused the formation of neurotoxin i.e acrylamide and thus of grave food safety
concern. The formation of this carcinogen (Tareke et al., 2002) in potato chips during
processing is directly linked with the maillard reaction (Mottram et al., 2002).
Therefore the right selection of potatoes for processing with respect to low
reducing sugar contents would be an important mitigation strategy against the
formation of this lethal compound.
Table-2a revealed the amount of nonstarch polysaccharides (as fibres) present
in different potato varieties. Desi produced maximum fibre contents ((7.830%)
followed by Chipsona (7.717%) and Cardinal (7.670%) with minimum recorded in
Hermes (6.430%). The ash Contents in the tubers were well differentiated and ranged
from 3.580 % in Desiree to 1.897% in Atlantic, and are highly correlated (R=0.898)
with their total mineral contents (Table-2b). Agria (577.5 mg/100g) and Desiree
(574.5 mg/100g) were preferred over all other varieties for their mineral composition,
followed by Cardinal (569.7 mg/100g) and Hermes (568.8 mg/100g) (Table-3),
however individual mineral dominance exhibited slight deviation from the general
trend.
76
4.1.3 Functional Attributes of Potato Varieties
Table-4a expressed the results on dry matter basis pertaining to the functional
characteristics of different potato varieties which are of the major food safety concerns
with positive correlation recorded in most of them. A close range of ascorbic acid
contents (78.50 mg/100g – 115.0 mg/100g) with non significant difference (P<0.05)
were recorded in the some of varieties, however maximum ascorbic acid contents were
recorded in Desi followed by Hermes and Desiree. Radical Scavenging Activity in
different potato varieties were significantly correlated (Table-4a) with other functional
parameters like Ascorbic acid (R= 0.802), Total Glycoalkaloids (R= 0.856) and Total
phenolic Contents (R=0.953). These results partly coincide with the findings of
Hejtmankova, et al., (2009). The maximum Glycoalkaloids which were estimated as
α-solanine were observed in Desi (22.35 mg/100g) followed by Hermes (19.66
mg/100g). Satellite accumulated maximum Chlorophyll contents (1.397 mg/100g)
followed by Agria and Desi (Table-4a) Glycolkaloids have been considered as one of
the toxins related to the human diet with upper safe limit of 20mg/100g on Fresh
Weight basis (Papathanasiou et al., 1999). However it is also believed to be a natural
defense mechanism in plants against some pathogens and insects (Rodriguez-Saona et
al., 1999). In all the tested varieties the amount of Glycoalkaloids were found lower
than the permissible limit considered safe for human intake. The significant
correlation between the Glycolkaloids and other functional components (Table-4b) in
selected potato varieties might be attributed to their anti malignant properties (Lee et
al., 2004). Amongst all Desi followed by Desiree and Agria attained maximum total
77
Table 4a Functional attributes of potato varieties (d.w basis).
Variety AA
(mg/100g)
TGA
(mg/100g)
CHL
(mg/100g)
TPC
(mgGAE/100g)
RSA
(%)
AGR 94.40 ±2.23 c 17.29±2.17 c 1.374±0.295 a 189.11± 8.66 c 59.92 ±0.73 b
ATL 80.50 ±1.15 f 15.34±2.02 d 1.037±0.236 cd 129.17± 9.82 g 38.95 ±0.17 g
CAR 82.00 ±2.05 ef 12.25±4.05 f 0.895±0.875 e 115.35±10.00 i 35.50 ±0.17 i
COU 83.00 ±1.55 e 14.17± 3.08 e 1.274±0.176 b 93.58± 5.77 j 37.54 ±0.17 h
CHI 76.45 ±1.15 h 11.40 ±4.05 g 1.013±0.231 d 125.74± 8.86 h 42.87 ±0.29 f
DESR 109.19 ±3.47 b 19.66±3.19 b 0.811±0.290 f 192.98± 6.06 b 59.29 ±0.15 b
DESI 115.00 ±4.66 a 22.23±2.20 a 1.292±0.115 b 253.24± 7.32 a 68.12 ±0.64 a
HER 110.00 ±3.88 b 19.24±4.06 b 1.089±0.522 c 150.33±10.55 e 52.50 ±0.58 d
LR 87.71 ±2.73 d 17.25±5.03 c 0.904±0.237 de 171.55± 6.32 d 56.90 ±0.16 c
SAT 78.29 ±2.30 g 12.55±3.11 f 1.397±0.583 a 132.96 ±13.01 f 44.74 ±0.81e
Dissimilar letters with in the column indicated significant difference (p< 0.05), Value ± corresponds to the standard error, d.w: Results expressed on dry weight basis.
AA (Ascorbic Acid), TGA (Total Glycoalkaloids), CHL (Chlorophyll), TPC (Total Phenolic Contents), RSA (Radical Scavenging Activity)
Table 4b Correlation between functional attributes
AA
TGA
CHL
TPC
RSA
AA 1 TGA 0.893 1 CHL -0.023 -0.001 1 TPC 0.784 0.845 0.102 1 RSA 0.802 0.856 0.129 0.953 1
78
phenolic contents and radical scavenging activity (Table-4a) with significant
correlation (R=0.953) between them (Table 4b). The results expressed were in close
confirmation with the finding of Lachmann et al. (2008).
4.1.4 Potato Chips Evaluation
Table-5a expressed post processing quality parameters like moisture contents,
fat absorption and sensory evaluation in different potato varieties. Mean moisture
contents (%) ranges between maximum (1.697%) in Desiree to the minimum (1.203%)
in Lady Rosetta. Maximum fat absorption (40.61%) was recorded in Desiree and
minimum (27.48%) in Atlantic. In general the fat absorption (%) in chips were
inversely proportional to the Dry matter contents as low fat absorption were recorded
in varieties like Atlantic, Lady Rosetta, Hermes, Agria, Courage, Chipsona etc. The
results were in close agreement with the findings of Kita, (2002). Different steps in
chip processing like peeling, cutting, slicing, washing and frying caused considerable
reduction (82.00% in Lady Rosetta – 76.73% in Desi) in glycoalkaloids in all the
tested varieties, which has also been reported by Peksa et al. (2006).
In general highly positive correlation was observed between all the sensory
attributes recorded by the judges (Table-5b). The response of judges regarding the
chip color was correlated with British Potato Council (BPC) chip chart to calculate the
approximate L-values. The best Chip color was displayed by Lady Rosetta (L-64.80)
followed by Agria (L-63.80)>Atlantic (L-63.20)>Hermes (L-63.10)>Courage (L-
63.0). The paramount color scores in Lady Rosetta is attributed to its low sugar and
protein contents thus also confirmed the findings of Kyriacou et al. (2008).
79
Table 5a Evaluation of potato chips
Variety CMC (%)
FAB (%)
TGA (mg/100g)
COL (L-value)
CRP Scores
FLV Scores
TAS Scores
AGR 1.289 ±0.21 e 30.67 ±3.15g 3.80 ± 0.34c 63.80 ± 1.32b 4.25 ±0.58de 4.10 ±0.57de 4.35 ±0.33cd
ATL 1.315 ±0.19de 27.48 ±2.30h 2.80 ±0.41e 63.20 ±1.84c 4.30 ±0.44cd 4.12 ±0.60d 4.33 ±0.10d
CAR 1.463 ±0.33c 37.45±2.71b 2.60 ±0.19f 61.08 ±2.81g 3.80 ±0.67 g 4.03 ±0.33e 4.06 ±0.33e
COU 1.327 ±0.44d 32.15 ±1.17f 2.87 ±0.18e 63.00 ±1.50d 4.20 ±0.58e 4.21 ±0.44c 4.00 ±0.23e
CHI 1.303 ±0.32e 32.95±2.92ef 2.48 ±0.15g 62.85 ±1.86de 4.25 ±0.60de 4.21 ±0.44c 4.39 ±0.47c
DESR 1.697 ±0.39a 40.61 ±5.71a 3.99±0.29b 60.40 ±2.87h 3.65 ±0.59h 3.10 ±0.58g 3.10 ±0.58h
DESI 1.513 ±0.11b 35.97 ±1.88c 5.20 ±0.26a 62.50 ±1.99e 4.00±0.74f 4.03 ±0.33e 3.50 ±0.58 g
HER 1.240±0.22 f 30.15±2.94g 4.04 ±0.30b 63.10 ±1.71cd 4.45 ±0.62b 4.36 ±0.19b 4.50 ±0.57b
LR 1.203 ±0.19g 27.77±1.80h 3.15 ±0.24d 64.80 ±0.91a 4.75 ±0.28a 4.85 ±0.12a 4.80 ±0.19a
SAT 1.467 ±0.45c 34.19 ±1.66d 2.46 ±0.21g 61.85 ±0.88f 4.00 ±0.33f 3.56 ±0.33f 3.86 ±0.88f
Dissimilar letters with in the column indicated significant difference (p< 0.05)
Value ± corresponds to the standard error
CMC (Chip Moisture Contents), FAB (Fat Absorption), TGA (Total Glycoalkaloids), COL (Color), CRP (Crispiness), FLV (Flavor), TAS (Taste)
80
Table 5b Correlation between potato chips attributes
MC
FAB
TGA
COL
CRP
FLV
TAS
MC 1
FAB 0.911 1
TGA 0.272 0.218 1
COL -0.893 -0.902 -0.003 1
CRP -0.921 -0.920 -0.101 0.947 1
FLV -0.894 -0.775 -0.099 0.863 0.880 1
TAS -0.959 -0.864 -0.394 0.812 0.877 0.867 1
81
Crispiness is an important quality feature in chip, mostly characterized by high Dry
matter and Starch contents. Potatoes with high specific gravity possessed
substantial starch contents along with higher molecular weight non starch
polysaccharides thus imparting stable, compact and thin configuration as also
mentioned by Kita, 2002. Lady Rosetta secured maximum crispiness scores (4.75)
followed by Hermes (4.45) > Atlantic (4.30) > Agria (4.25) > Chipsona (4.25).
Almost the same trend followed in the taste and flavor scores recorded by the panel
of judges (Table-5a) Lady Rosetta maintained it supremacy over all other varieties
with maximum flavor (4.85) and taste (4.80) Scores followed by Hermes.
4.2 EFFECT OF DIFFERENT PACKAGING MATERIALS ON THE
QUALITY ATTRIBUTES OF POTATO
As first experiment of 2nd phase of study the efficiency of different
packaging materials like jute, nylon, polypropylene, cotton, low density
polyethylene, medium density polyethylene and high density polyethylene were
studied along with control on the premium potato variety “Lady Rosetta” (selected
in the first phase). Physico-chemical and functional assays of potato tubers and
processing performance of potato chips were evaluated at an interval of seven and
fourteen days respectively.
4.2.1 Effect on Weight Loss (%)
The general trend was an increase in weight loss (%) in all the treatment;
however the rate of weight loss was slower in packaged potato as compare to
control during the storage period. Treatment means of packaged potato showed
non significant difference between T2 and T8, T4 and T6 while all other differed
significantly. Data on weight loss revealed significant differences between all the
82
storage means. The interaction between treatment means and storage intervals
showed maximum weight loss (%) in T1 and minimum in T6 at the end of storage
(Fig. 1).
Maximum weight loss was recorded in control (T1) while poly propylene
packaging (T4) showed minimum weight loss till the end of nine week storage at
ambient temperature. In general potato packed in different polyethylene
packagings (T6, T7, T8) showed lesser weight loss as compare to jute, nylon and
cotton packagings i.e T2, T3 and T5 respectively. Amongst all the treatments weight
loss during different storage intervals showed slow initial increase (0.89 to 1.252
%) till fourth week which subsequently progressively ascended up to 6.619 and
10.90 % in T1 and T4 respectively till the end of 63rd day (Fig 1). This slow initial
increase in weight loss presented non significant interaction between storage
intervals and treatments during early week’s storage which became significant
after sixth week till the end of storage.
The loss of water activates the series of complex metabolic activities thus
considered as an important stability index for the storage life assessment in fruits
and vegetables. The weight loss in potato is attributed to the water loss through
peel tissues due to physiological processes like respiration and sprouting (Tester et
al., 2005). Different post harvest management techniques are employed in order to
increase the storage stability of horticultural commodities like modified
atmosphere packaging, controlled atmosphere packaging, coatings, irradiation etc
(Abbasi et al., 2004). Controlled atmosphere storage has not been considered
suitable for potato storage due to its high rate of respiration under elevated carbon
dioxide level (Fonseca, 2002).
83
0
2
4
6
8
10
12
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
Wei
ght
loss
(%
)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 1 Weight loss in potato under different packagings showing minimum loss in polypropylene and LDPE during storage
(LSD (0.05) for treatment = 0.0509 LSD (0.05) for interval = 0.0570 LSD (0.05) for interaction = 0.1613)
Vertical bars show ±SE of means.
84
Different modified atmosphere packaging has been evolved as an inexpensive and
most appropriate alternate (Tuil, 2000) to reduce gaseous exchange and water loss
during storage. Packaging systems confer barrier properties to the physiological
gaseous exchange and resulted in eventual decreased weight loss under storage
period (Hong et al., 2003).
Minimum weight loss during the present study in packaged potato was
primarily due to high moisture level and restricted gaseous exchange maintained
inside as compare to control. The permeability and type of different packaging
materials however showed significant difference in their physiological weight
losses during the storage. In potato packed in polyethylene packaging ( T6, T7, T8)
the weight loss increases with the increase in the thickness as increased weight loss
has been observed in high density polyethylene packaging as compare to those
packed in low density polyethylene. The similar information regarding thickness
and permeability of packaging material has been reported by Rakotonirainy et al.,
(2001). The application of polyethylene packagings in different horticultural
products like potato (Rosenfeld et al., 1995), tomato (Sammi and Masud, 2007),
mango (Abbasi et al., 2011) apricot (Ibrahim, 2005), loquat (Chen et al., 2003) etc.
have been found effective in decreasing weight loss during their post harvest
storage. Conte et al. (2009) reported best storage stability under polypropylene
based packaging in cherries. Similar results regarding efficacy of polypropylene
packaging during post harvest storage has been reported by Calderon et al. (2008).
Minimum weight loss in potato stored in low density polyethylene packaging (T6)
and polypropylene packaging (T4) as compare to other packaging materials and
control confirmed the finding of the researchers reported above.
85
4.2.2 Effect on Total Soluble Solids
Data pertaining to the total soluble solid (TSS) in potato exhibited general
increase during the storage period. The increase in TSS was more pronounced in
T1 as compare to all other treatments. Treatment means indicated minimum
retention of TSS in T4, followed by T2, T3 and T6 with non significant difference
recorded between them. Storage interval means showed significant difference in
TSS except during the first and second weeks and maximum retention was
observed in case of ninth week storage. In general non significant interaction
between treatment means and storage intervals means became significant after
the third week storage (Fig. 2).
TSS accumulation in all the packaging materials was steady during the
early weeks which progressively increased with the increase in storage duration.
Maximum retention of TSS value estimated in control (6.34obrix) and HDPE (6.26
obrix) packaging, while minimum accumulation observed in jute (6.07obrix) and
polypropylene (6.11obrix) packagings at the end of ninth week storage. TSS values
remained statistically similar amongst all other packaging at the end of storage
period. Overall different packagings retained lower TSS accumulation as compare
to control.
Total soluble solids in fruits and vegetable primarily correspond to the
presence of soluble sugars, salts, acids etc. however the change in TSS is
predominantly related with sugar metabolism during the post harvest storage.
86
5.50
5.70
5.90
6.10
6.30
6.50
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
Tot
al s
olu
ble
sol
ids
(oB
rix)
Control
Jute
nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 2 Total soluble solids in potato under different packagings showing highest increase in control during storage
(LSD (0.05) for treatment = 0.0058 LSD (0.05) for interval = 0.0180 LSD (0.05) for interaction = 0.0510)
Vertical bars show ±SE of means.
87
Changes in TSS are directly related with the hydrolytic conversion of
insoluble starch polymers into soluble sugars during the post harvest period (Kittur
et al., 2001). In general conversion of starch into sugar is an important index of
ripening in most of the climacteric fruits. Physiological conversion of starch into
sugars in potato is slower as compare to other fruits and vegetable and is
specifically undesirable due to the eventual loss of color in processed products
(Tamaki et al., 2003).
Different packaging materials are known to reduce water loss and starch
hydrolysis due to lower respiration rate inside storage atmosphere consequently
retained lower TSS accumulation as compare to control. Increased TSS
accumulation in control might be due to concentration effect because of increased
water loss with subsequent soluble solute accumulation in cell vacuoles. These
results were in line with the findings of Munoz et al (2006) who reported low TSS
accumulation under controlled rate of respiration. Several other researchers also
reported that modified atmosphere packaging resulted in controlled conversion of
starch into sugars in tomato (Sammi and Masud, 2007), guava (pervez et al.,
1992), oranges (Attia, 1995) which are in line with the findings of present
investigations.
4.2.3 Effect on pH
Data related to pH in potato exhibited decrease with the increase in storage
period however the rate of decrease in pH was faster in T1 as compare to all other
treatments. Treatment means showed maximum pH retention in T4 followed by T7
and T6, while minimum pH was recorded in T1 and T3 while T5 and T8 were found
statistically similar. Significant statistical difference was recorded in all the Storage
88
5.7
5.8
5.9
6
6.1
6.2
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
pH
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 3 pH in potato under different packagings showing maximum retention in polypropylene and LDPE during storage
(LSD (0.05) for treatment = 0.00510 LSD (0.05) for interval = 0.00570 LSD (0.05) for interaction = 0.01613)
Vertical bars show ±SE of means.
89
interval means. Storage interval means progressively decreased from first week till
the ninth week storage. The interaction between treatment means and storage
intervals revealed significant difference at α = 0.05 (Fig. 3).
Minimum retention of pH value found in Control (5.76) followed by
cotton packaging (5.79) at the end of 63rd day storage. Highest pH value
estimated in potato packed in MDPE packaging (5.97) followed by polypropylene
packaging (5.96). Potato packed in LDPE and Jute packagings also retained
appreciable pH value at the end of storage time. The pH decline in jute packaged
potato remained steady through out the storage period and maintained reserved
value by the end of storage.
Considerable decline in pH observed in control by the start of 4rth week i.e
6.10 to 6.04 while the same happened to most of other treatments by the start of
sixth week. Potato packaged in different polyethylene packaging, polypropylene
packaging and cotton packaging revealed the onset of decline in pH by the start of
third week. In terms of relative change the decline in pH by ninth week storage
observed in polypropylene and MDPE packaging was similar to that quantified in
control on seventh week. The considerable response of stored potato to different
packaging systems revealed their efficacy in post harvest management of this
valuable crop
pH measures the available hydrogen ion concentration and carries anti
microbial characteristics in the pulp of fruits and vegetable and their slight change
cause considerable change in electrolyte concentrations (Olsson et al., 2004).
Reduction in pH value was observed in all the samples which entails that the
potato tubers turned more acidic with the increase in storage period. In general
90
packagings retained higher pH value than the control due to the better retention of
total acids which inturn increasd the hydrogen ion concentration. The variation in
pH value with in different packagings might be due to their type and permeability
in holding these organic acids during storage. Similar observations have been
recorded by Babarinde and Fabunmi (2009) regarding better retention of pH in
LDPE packaged vegetables than in control. In addition pH retention during storage
as result of improved packagings like polypropylene, LDPE maintained the
horticultural commodities more resistant to decay and microbial attack thus
improved the storage stability which was also observed in the present
investigations. The decline in pH during storage alone or in response to different
packaging systems has also been reported by different researchers in potato
(Nourian et al., 2003), mango (Manzano et al., 1997) and tomato (Sirinivasa et al.,
2006). Some researchers have reported decrease in pH of potato slices intend for
processing may cause low acrylamide formation in final products (Jung et al.,
2003). This is however achieved by intentional soaking of potato slices in different
organic acid solutions prior to frying (Pedreschi et al., 2004).
4.2.4 Effect on Specific Gravity
The general trend was an initial increase in specific gravity in potato
followed by a gradual decline till the end of storage. The rate of decline in specific
gravity value was higher in T1 as compared to other treatments. Treatment means
revealed non significant difference in most of the treatments except control.
Storage Interval means remained statistically same at early and mid storage period
however differed significantly at the end. In general except in T1 interaction
between treatments and storage intervals was also found non significant (Fig. 4).
91
1.095
1.1
1.105
1.11
1.115
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
Sp
ecif
ic G
ravi
ty
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 4 Specific gravity in potato under different packagings showing maximum value in LDPE during storage (LSD (0.05) for treatment = 0.001613 LSD (0.05) for interval = 0.001800 LSD (0.05) for interaction = 0.005099)
Vertical bars show ±SE of means.
92
Specific gravity value progressively increased with the storage period by
the fourth week and than gradually decreased till the end of storage period. Potato
packed in polypropylene packaging (T4), LDPE packaging (T6), MDPE packaging
(T7) and HDPE packaging (T8) retained maximum value during fourth, fifth, and
sixth week storage. T6 retained maximum specific gravity value (1.106) in contrast
to control (1.100) by the end of ninth week. Over all results revealed that different
packaging systems had statistically no significant effect on the specific gravity
value up to ninth week storage.
Specific gravity is largely associated with the total dry matter content in
potato as promising co relation (R= 0.93) has been reported by Kumar et al.
(2005). The observed changes in specific gravity can be associated with the
changes in their dry matter contents which are primarily referred to the starch
contents present in potato.
In all treatments during initial weeks slight increase in specific gravity
value had been observed as freshly cured potatoes favored the formation of dry
matter (Kaul et al., 2010). Rivero et al. (2003) reported that post harvest storage of
potato at ambient temperature is characterized by concurrent processes like
transpiration and starch degradation resulted in simultaneous increase and decrease
in dry matter contents respectively. In the present study starch losses are
compensated by water loss due to evapo-transpiration causing over all negligible
change in specific gravity as happened during most of storage period. In later
stages of storage the rate of starch degradation exceeds the rate of water loss in
different treatments in general and in control in particular causing significant
decrease in specific gravity. Hydrolysis of starch is accelerated by the sprouting in
93
all potato except in those packed in polyethylene packaging and polypropylene
packaging causing eventual decrease in their specific gravity values. These results
confirm the previous observations reported by Biemelt et al (2000). Packaging
decreased the consumption of respiratory substrate i.e starch, sugars, and organic
acids and lowered the rate of transpiration (Ding et al., 2002) due to barrier
properties resulted in higher specific gravity retention in packaged potato as
compare to control at the end of storage period.
4.2.5 Effect on Glucose
The effect of different packaging materials on glucose contents revealed
steady increase through out the storage period however, the rate of increase in
glucose contents varied with the type of packaging material. Treatment means
showed significant difference in stored potato with T1 retained maximum while T6
retained minimum glucose contents. Storage interval means also revealed non
significant difference with maximum value recorded in the last week while
minimum during first week storage. The interaction between storage intervals and
treatments revealed less significant difference at the start of storage however
significant difference have been recorded at the later stages of storage (Fig. 5).
Steady increase in glucose contents had been observed in potato during
storage however the increase was more pronounced in case of control. The rate of
increase in glucose level in control started by the fourth week and gradually
increased up to 0.333% by the end of storage. Non significant difference had been
recorded in LDPE packaging and MDPE packaging during storage period both
attained almost 0.2% glucose contents by ninth week storage. Rapid increase in
94
glucose contents had been recorded in HDPE packaging by sixth week storage the
same was also observed in potato packed in jute and nylon packaging. Least
glucose contents had been estimated in polypropylene packaged potato which
maintained the level around 0.2% by the end of storage.
Increase in the glucose contents with in the treatments during the potato
storage was found mostly consistent with the increase in the total soluble contents
(Fig. 5). The phenomenon might be due to the partial degradation of starch into
sucrose followed by the subsequent formation of more soluble sugars like glucose
and fructose (Baldwin, 2011). The degradation of insoluble starch into soluble
sugars has important inference in the tuber quality. The process founds the
availability of respiratory substrates (i.e. glucose) along with the tuber sweetness
which leads to the poor storage stability and adverse color in processed products
respectively as also been observed in the control. The amount of reducing sugar
contents in potato intending for processing is very critical since it sets the frying
color in fried potato products like chips, French fries etc. Both glucose and fructose
being reducing sugars in potato have been negatively correlated with chip fry color
(Blenkinsop et al., 2002) however the presence of glucose content are of major
food safety concern due to their active participation in toxic acrylamide formation
at elevated temperature processing (DeWilde et al., 2004). Biedermann-Brem et al.
(2003) reported that potato destined for frying, roasting or baking should contain
maximum of 0.1% reducing sugars to mitigate likely acrylamide formation. The
significant increase in glucose contents at the later stage of storage in treatments
like control, T2, T3, T5 and T8 might be due to the depletion of carbohydrates
reserves in the potato tubers close to their sprouting (Sowokinose, 1990).
95
0
70
140
210
280
350
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
Glu
cose
(m
g/10
0g)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 5 Glucose in potato under different packagings showing lowest contents in polypropylene during storage (LSD (0.05) for treatment = 1.970 LSD (0.05) for interval = 2.203 LSD (0.05) for interaction = 6.231)
Vertical bars show ±SE of means.
96
Potato packed in Polypropylene, LDPE and MDPE packagings delayed the
dormancy break as compare to other treatments thus retained lower soluble sugar
contents till the end of storage. The results presented in the present study lies in
close confirmation with the findings of Fauconnier et al., (2002).
4.2.6 Effect on Total Sugars
Response of potato packaging to their total sugar accumulation was almost
consistent with the pattern of glucose accumulation during storage. The total sugar
accumulation took place at steady rate which increased till the end of storage
period. Treatment means demonstrated significant difference between packaged
potato and those placed as control, while non significant difference was recorded
between T2 and T4, T3 and T7. Storage interval means showed significant difference
between all values with maximum sugar retention at the end of storage. The
interaction between treatment means and storage intervals exhibited slow initial
increase with relatively stable values during the mid storage weeks. The
significant increase in sugar contents had been observed by the start of sixth
week storage being found more momentous in T1, T3, T5 and T8 (Fig. 6).
Maximum increase in total sugar contents was recorded in control (.82% to
1.14%) followed by the potato packed in cotton (1.089 %), nylon (1.039%) and
HDPE (1.107%) packagings. Potato packed in LDPE packaging, polypropylene
packaging, and jute packaging retained 0.925%, 0.934% and 0.959% total sugar
contents respectively.
Total sugar contents are present in potato primarily in the form of non-
reducing sucrose and reducing glucose and fructose (Blenkinsop et al., 2002).
97
750
850
950
1050
1150
1250
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
Tot
al s
uga
r (m
g/10
0g)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 6 Total sugar in potato under different packagings showing lowest contents in polypropylene and LDPE during storage (LSD (0.05) for treatment = 5.041 LSD (0.05) for interval= 5.636 LSD (0.05) for interaction = 15.94)
Vertical bars show ±SE of means.
98
The increase in these soluble carbohydrates leads to the increase in total
soluble solids contents of potato tubers which was also pragmatic in the present
study. This steady increase in the total sugar was found consistent with the increase
in total soluble solids during storage which has also been reported by Vela et al.
(2003). Although the role of sucrose in browning of fried potato products is limited
but it may functions as transitory balance in starch degradation process during
storage. The hydrolysis of sucrose mediated through enzyme invertase may leads
to the formation of glucose and fructose monomers (Kumar et al., 2004).
The presence of either kind of sugars is highly undesirable for the industrial
and consumer requirement. Amongst different polyethylene packagings employed
in the present study HDPE packaging was found to be ineffective in permitting
sugar accumulation during storage which might be due to its limited permeability.
The maximum sugar retention was reported at the end of storage period in control
which might be due to their closer to dormancy break at the twilight of storage
period these findings accede the same as stated by Sowokinose (1990) and
Fauconnier et al., (2002).
4.2.7 Effect on Starch
The variation in starch contents in response to different packaging material
revealed steady initial increase followed by progressive decline during the storage
period. Data related to treatment means showed minimum starch accumulation in
T1, T3 and T8 which were found statistically similar. Maximum starch contents
were retained in T4 followed by T6 and T7. Storage interval means expressed
99
significant difference between them with non significant difference was established
between first and third week storage. Interaction between storage interval and
treatment showed maximum starch retention during second week storage. Starch
contents estimated by ninth week storage in T4 were statistically similar to those
achieved in T1 by the start of 6th week storage (Fig. 7).
Maximum starch contents were observed during second week of storage
with non significant difference was observed in all the treatments with potato
packed in LDPE and polypropylene packaging retained maximum 20.33% and
20.10% starch contents respectively. Appreciable retention of starch contents had
been observed in polypropylene packaging (17.17%) followed by LDPE packaging
(16.80%) and Jute packaging (16.57%) by the end of storage period. The
percentage depletion in starch contents by the end of storage in different packaging
systems was found minimum in polypropylene packaged potato i.e 12.5% as
compare to 21% in control.
The textural attributes in potato tubers like consistency, mealiness,
sloughing etc are largely associated to its starch properties and subsequent changes
during the processing. During physiological growth stages the sugar produced in
the potato leaves are translocated to the growing tissues and stored in the form of
starch (Fernie et al., 2002). During storage transpiration, redistribution and
respiration in potato tubers may effect their starch concentrations. The hydrolysis
of starch molecules is mediated through the activities of gluco-amylases breaking
the α-1→6 links of amylopectin generating linear molecules of amylase which
subsequently hydrolysed by invertase and amylases to produce sucrose and
reducing sugars respectively (Marchal, 1999). The starch hydrolysis however
provides sufficient energy for the growth and development of sprouts (Hentschen
and Sonnewald, 2000).
100
15
16
17
18
19
20
21
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
Sta
rch
(%
)
Control
Jute
Nylon
PolypropyleneCotton
LDPE
MDPE
HDPE
Fig.7 Starch in potato under different packagings depicting maximum decline in control and nylon during storage
(LSD (0.05) for treatment = 0.2027 LSD (0.05) for interval = 0.2266 LSD (0.05) for interaction = 0.6410)
Vertical bars show ±SE of means.
101
In the present study maximum starch depletion in control and some other
treatments closer to sprouting confirmed the above reported findings. The use of
suitable packaging materials like polypropylene and LDPE packaging was found
efficient in sprout prevention thus retained maximum starch contents by the end of
storage period.
4.2.8 Effect on Ascorbic acid
In response to different packaging systems the ascorbic acid (AA) was
among the parameters, which decreased with the increase in storage time. The
decrease was highly significant in control as compare to all other treatments.
Treatment means revealed maximum AA retention in T4 and T6 which were found
statistically similar at 5% level of significance. Treatments T2, T7 and T8 also
maintained appreciable AA contents as compare to control. Storage Interval means
showed significant difference in their AA contents with maximum value retained
during first week storage and minimum during the last week. The interaction
between storage intervals and treatments showed substantial AA retention in
packaged potato as compare to control. AA contents observed by at the end of
storage in T4 and T6 were found greater than those identified in sixth week storage
in control (Fig. 8).
Amongst different treatments, potato packed in polypropylene packaging
and LDPE packaging retained maximum AA contents by the end of storage period.
The reductions in AA by the end of storage in PP packaging and LDPE packaging
were 26% and 29% respectively as compare to control i.e. 42%. In general the
maximum reduction in AA contents was observed during the last three weeks
storage. Moderate reduction of AA was observed in potato packed in MDPE, Jute
and Nylon i.e 31.75%, 32.5% and 33.0% at the end of storage period.
102
14
16
18
20
22
24
26
28
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
Asc
orbic
Aci
d (m
g/10
0g)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 8 Ascorbic acid in potato under different packagings showing highest retention in polypropylene during storage
(LSD (0.05) for treatment = 0.2364 LSD (0.05) for interval = 0.2643 LSD (0.05) for interaction = 0.7477)
Vertical bars show ±SE of means.
103
Ascorbic acid is one of the most important water soluble vitamins required
in human diet and much of it is supplied by fresh fruits and vegetables. It is the
predominant vitamin in potato and of significant functional importance (Davey et
al., 2000). Depletion of ascorbic acid has been implicated with reduced nutritional
quality therefore their assured stability during storage has been focal concern for
post harvest technologists (Larisch et al., 1996). Hagg et al. (1998) reported that
AA contents significantly decreases during storage of potato. The reduction is
ascribed to the oxidation of ascorbic acid into dehydro ascorbic acid and afterward
to diketo-gluconic acid. Being water soluble vitamin and succeptable to oxidation
AA contents rapidly decreased with the increase rate of respiration and subsequent
water loss.
Facts framed in the present study revealed continuous reduction in AA
contents which was found extensive in control. The application of different
packaging systems especially of Polypropylene and polyethylene material reduced
the rate of water loss from potato and conferred barrier to the gaseous exchange
thus preventing the loss and oxidation of ascorbic acid as compare to control. The
efficacy of modified atmosphere packaging in retention of high AA contents in
fruits and vegetables have also been reported by Conte et al. (2009), Calderon et
al. (2008) and Sammi and Masud, (2007).
4.2.9 Effect on Total Glycoalkaloids
Total Glycoalkaloids (TGA) accumulation in terms of solanine equivalent
showed an increasing trend during nine week storage in all the treatments. The
104
increase in TGA was more pronounced in control as compare to packaged
potatoes. Treatment means revealed significant difference between various
packaging materials in their TGA contents. Maximum and minimum TGA contents
during storage period were identified in T1 and T7 respectively. Storage interval
means showed significant difference in their TGA contents and found maximum at
the end of storage. The interaction between storage intervals and treatments
showed maximum TGA accumulation by ninth week storage in control and
minimum in all the treatments during the 1st week storage (Fig. 9).
Results expressed on dry weight basis showed increase in TGA content in
potato tubers during storage however, in all treatment except in control the TGA
level remained under safe limit i.e. 20mg/100g f.w as suggested by
Papathanasiou et al. (1999). In general irrespective of packaging type
considerable increase in TGA contents has been recorded by fourth week
storage which continued till the end of storage. The increase in TGA in
control by the last week of storage was about eight folds (7.50 mg to 63.80
mg) as compare to around six folds (7.50 mg to 47.20 mg) increase in potato
packed in Polypropylene packaging. TGA contents increased up to 53.70
mg/100g d.w and 51.20 mg/100g d.w in Cotton and HDPE packaging
respectively by ninth week storage. Potatoes in jute, LDPE and MDPE
packaging also retained moderate TGA contents as compare to control.
The increase in TGA contents under different storage conditions and
packaging system has also been reported by different researchers. Nema et
al. (2008) reported increase in TGA contents during storage under different
packaging systems. He proposed that the color, type and permeability of the
105
5
15
25
35
45
55
65
75
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
TG
A (
mg/
100g
d.w
)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 9 Total Glycoalkaloids in potato under different packagings showing maximum increase in control during storage
(LSD (0.05) for treatment = 0.4009 LSD (0.05) for interval = 0.4482 LSD (0.05) for interaction = 1.2680)
Vertical bars show ±SE of means.
106
packaging material effect TGA formation during storage. Similar
observations regarding the effect of different packaging materials on TGA
contents has been documented by Rosenfeld et al. (1995) and Gosselin and
Mondy, (1989). In the present study potato showed visible sprouts or closed
to sprouting retained high level of TGA contents which also confirmed the
previous findings of Sengul et al. (2004) and Kozukue et al. (2001).
4.2.2.10 Effect on Total Phenolic Contents
Total Phenolic Contents (TPC) showed initial increasing trend which
started to decline by the end of storage period. Considerable decline in TPC
was observed in control as compare to packaged potatoes. Treatment means
showed significant difference in TPC in response to different packagings. T4
and T7 maintained maximum TPC while minimum were observed in T1.
Storage Interval means expressed significant difference with maximum
determined in fifth week while minimum estimated in first week. The
interaction between treatments and storage intervals showed maximum TPC
contents in T1 and T4 during fourth and seventh week storages respectively
(Fig. 10).
Considerable increase of around 30% in TPC had been observed in all
treatments by sixth week storage, which progressively declined by the end of
storage. The decline in TPC was more significant in control, nylon, HDPE,
and cotton packaged potatoes and almost corresponded to the TPC contents
reported in first week. After ninth week storage potatoes stored in the
107
70
90
110
130
150
170
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
TP
C (
mg
GA
E /
100g
d.w
)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 10 Total phenolic contents in potato under different packagings showing maximum retention in polypropylene during storage (LSD (0.05) for treatment = 0.8727 LSD (0.05) for interval = 0.9757 LSD (0.05) for interaction= 2.7605 )
Vertical bars show ±SE of means.
108
polypropylene, LDPE, Jute and MDPE packaging retained 137.23 mg,
130.23 mg, 124.07 mg and 120.50 mg TPC respectively in contrast to
control presented around 88.77 mg TPC.
Total phenolic contents are bioactive compounds responsible for
various significant physiological processes like enzyme activity, nutrient
uptake, protein synthesis (Robbin, 2003). They acts as substrate in potato
browning mediated through the activities of poly phenol oxidase (PPO)
enzymes and molecular oxygen followed by subsequent melanin formation
(Anthon and Barrett, 2002). High retention of TPC during storage is attributed
to low PPO and momentous anti oxidant activity in potatoes (Lachman et al.,
2008). During storage TPC contents in potato continued to increase
(Madiwale et al., 2011) till the on set of PPO activity. The presence of ample
molecular oxygen in control caused significant decline in TPC as compare to
other treatments. Our results indicated that packaging materials in general
and LDPE and PP packaging in particular curtail the decline in TPC as
compare to control which are also inline with the finding of Gonzalez et al.
(2004).
4.2.11 Effect on Radical Scavenging Activity
Radical scavenging activity (RSA) determined in terms of %
inhibition of DPPH showed slight initial increase followed by gradual
decrease during potato storage. The decrease in RSA was however less
pronounced in packaged potato as compare to control. Treatment means
showed T6 maintained maximum activity followed by T7, T4 and T8 while T1
demonstrated minimum activity. T2, T3 and T5 were found statistically
109
similar and expressed moderate activities during storage. Storage interval
means showed maximum activity during second and third weeks storage
which progressively decreased with time and minimum activity was found in
the last two weeks of storage. Interaction between treatment means and
storage interval showed maximum activity during second week storage in
most of treatments except in control, jute and cotton packaging.
Considerable reduction in activity had been observed between third and
fourth weeks storage (Fig.11).
Radical scavenging activity increased during first week and attained
maximum by second week in all the treatments. The decline in activity was
observed during fourth week which is more articulated in control as compare
to other treatments. Potato packed in polypropylene and polyethylene
packaging retained substantial activity after fourth week till the end of
storage period with non significant difference recorded between them. The
loss in activity after maximal second week till the end of storage in PP and
LDPE packaging was 56% and 59% in contrast to control with 69%. PP
packaged potatoes retained maximum activity i.e 23.87% followed by LDPE
and MDPE packaged potatoes with 23.23% and 22.63% by the end of
storage. The percentage loss in RSA was lesser during the last three weeks
storage as compare to initial storage weeks.
Fruits and vegetables owing to their rich vitamins and poly phenolic
contents reportedly carry high radical scavenging activity which corresponds
to their anti oxidant potential (Kondo et al., 2005). Anti oxidant have the
capacity to quench free radical and protect the biological system against
their potential detrimental effects (Diplock, 1998).
110
10
20
30
40
50
60
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
RSA
(%
) Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 11 Radical scavenging activity in potato under different packagings showing highest activity in polypropylene during storage (LSD (0.05) for treatment = 0.2949 LSD (0.05) for interval = 0.9209 LSD (0.05) for interaction = 2.6050)
Vertical bars show ±SE of means.
111
Predominant anti oxidant compounds present in fruits and vegetables
includes phenolic compounds, flavonoids, carotenoids, ascorbic acids and
tocopherols (Toit et al., 2001). The maximum retention of these anti oxidants in
fruits and vegetable enable them to attain longer storage life with appreciable
nutritional attributes. Amongst different techniques to extend post harvest storage
life in perishables Modified atmosphere packaging is considered as cheap and
effective (Banaras et al., 2005). Packaging improves the retention of phenolics,
ascorbic acid and other functional component during the post harvest storage
(Barth and Zhang, 1996).
Significant correlation between phenolic contents and anti oxidant
activity (RSA) can also be distinguished between Fig 10 and Fig 11 in response
to different packagings during initial weeks of storage. The DPPH assay
employed in the present study for anti oxidant activity corresponds to the
presence of non enzymatic antioxidants like phenolics (Art and hollman, 2005)
and ascorbic acid (Kojo et al., 2004) as estimated during the storage. In the
present investigation initial increase in activity might be due to the increase in
total phenolic contents (Padda and Picha, 2008) along with the ample presence
of ascorbic acid contents in freshly cured potato. However this correlation trend
did not remain the same after the mid storage due to the earlier depletion of
ascorbic acid as compare to the stable phenolics. This phenomenon was found
more pronounced in the control as compare to packaged potatoes due to the rapid
loss of ascorbic acid during the first half of storage. Minimum percentage loss
in RSA was reported during last three weeks of storage and was specifically
attributed to packaged potatoes. The possible reason might be due to the
112
regeneration of anti oxidant compounds like ascorbic acids in potato to
counter balance the increased free radicals produced during senescence. The
better immune response in packaged potatoes maintained efficient RSA
activity at the twilight of storage period as compare to control. The improved
immune response under different packaging was also reported by Sonia and
Chavez, (2006). The use of different packaging materials on potato expressed
maximum anti oxidant activity due to greater retention of ascorbic acids, phenols
and other functional compounds. Ding et al. (2002) and Piga et al. (2002)
reported high antioxidant activity in fruits packed in modified atmosphere
packaging as compare to control as reported in the present study.
4.2.12 Effect on Polyphenol Oxidase Activity
Results pertaining to the effect of different packaging materials on the
poly phenol oxidase (PPO) activity in potato generally showed steady increase
with the extension in storage period. The increase in activity was found
prominent in control as compare to packaged potatoes. Treatment means
demonstrated maximum activity in T1 while minimum was recorded in T4 and T6
and were found statistically similar. Moderate PPO activity were observed in
treatments T2 and T8 and also found statistically similar during the storage.
Storage interval means showed significant difference in their PPO activity with
maximum and minimum values estimated on 63rd and 1st day respectively.
Interaction between storage intervals and treatments was significant with
maximum activity estimated in T1 after 1st month till the end of storage (Fig.12).
113
30
37
44
51
58
65
72
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
PP
O (
U/g
f.w
)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 12 Polyphenol oxidase in potato under different packagings maintaining lowest enzymatic activity in LDPE during storage (LSD (0.05) for treatment = 0.2755 LSD (0.05) for interval = 0.3081 LSD (0.05) for interaction =0.8713)
Vertical bars show ±SE of means.
114
Steady increase with non significant difference in PPO activity had been
noticed in all the treatments till 1st month storage except in control where activity
started to increase after 21st day on wards. The PPO activity increased at rapid
rate after fourth week till the end of storage in all treatments. The enzyme activity
recorded in control on 35th day was higher than that estimated in all other
treatments by the end of storage period. Lowest PPO activity had been noticed in
PP, LDPE and MDPE packaged potatoes as compare to all other treatments and
were found statistically similar during most of storage time. PPO activity
increased more than 2-folds in control with maximum recorded PPO activity i.e
68.57 U/g in contrast to minimum 44.73 U/g in LDPE packaged potato at the end
of storage time.
PPO activity increases in potato due to the availability of substrate and its
subsequent oxidation during storage. The non significant changes during the 1st
month storage in most of the treatments might be due to absence of physical
damages due to their appropriate curing and subsequent careful post harvest
handling as also observed by Nourian et al. (2003). The increased PPO activity in
fruits and vegetable during post harvest storage might be attributed to moisture
loss and senescence (Bryant, 2004). In the present study application of different
packaging materials effectively maintained modified atmospheric conditions
around potato as compare to control resulted in lower moisture loss and limited
oxygen availability for poly phenol oxidations.
115
The variation in PPO activity with in different packaging materials might
be attributed to their type and permeability (Rakotonirainy et al., 2001). The
significant increase in the PPO activity in different treatments by 4rth week till
the end of storage might be attributed to the high substrate availability yet
packaging materials conferred barrier properties to substrate oxidation resulted in
low eventual activity as compare to control. Kader, (2002) reported substrate
inhibition for PPO enzymes under modified atmosphere packaging which lead to
low PPO activity during storage. These effective barrier properties in different
packaging materials like polyethylene, polypropylene, polystyrene have also been
reported by Joyce and Patterson (1994).
4.2.13 Effect on Peroxidase Activity
Effect of different packaging materials on peroxidase (POD) activity in
potato showed a steady increase in all the treatments during storage however the
increase was highly prominent in control as compare to other treatments (Fig.
13). Treatments means revealed maximum activity in T1 while minimum in T6.
Non significant difference had been observed in T2 and T3 whereas T5 and T8
were also found statistically similar. Storage interval means showed maximum
and minimum activity during last and first week respectively. Interaction between
storage intervals and treatment was significant with maximum activity estimated
in T1 on 49th day onwards till the end of storage (Fig.13).
116
In general POD activity steadily increased in the potato tubers during the
storage and found crumb consistent to their PPO activity. Maximum activity
POD activity (32.40 U/100g) was estimated in control and minimum (23.20
U/100g) in LDPE at the end of storage. PP and MDPE packaging retained
comparatively low POD activity 23.43 U/100g and 26.47 U/100g respectively
during the same storage periods. In comparison the POD activity estimated in T4
and T6 at the end of storage was found lower than that calculated in T1 on 42nd
day storage.
Enzymatic browning in potato may cause substantial loss by deteriorating
nutritional and sensorial attributes during storage. The phenomenon is primarily
associated with the activities of peroxidase and polyphenol oxidase enzymes
(Loaiza and Saltveit, 2001). POD being thermally stable and omni present in
different part of plants has wide range of substrate based activity than PPO
(Anthon and Barrett, 2002). The increased POD activity is associated with the
oxidation of phenolic compounds under physiological stress causing decay and
loss of quality during storage (Ding et al., 2006). In addition they also have
known to exhaust immune system by degradation of natural anti oxidants i.e
peroxides and consequent liberation of free radicals (Rojas et al., 2007). Both
these processes mediated through peroxidase activity accelerate browning in
potatoes and affect the ultimate postharvest storage life.
117
12
16
20
24
28
32
36
1 7 14 21 28 35 42 49 56 63
Storage intervals (day)
Per
oxi
das
e (U
/100
g f.
w)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 13 Per oxidase in potato under different packagings maintaining lowest enzymatic activity in polypropylene and LDPE during storage (LSD (0.05) for treatment = 0.2717 LSD (0.05) for interval = 0.3038 LSD (0.05) for interaction = 0.8593)
Vertical bars show ±SE of means.
118
POD is considered thermally more stable than PPO thus their activity inhibition
is considered as index of proper blanching in food processing. Aydin and
Kadioglu (2001) reported increased POD activity in fruits and vegetables under
stress conditions and with the progression in their physiological stages i.e.
ripening, senescence which has also been observed in different treatments at the
end of storage period.
Application of different packaging materials maintained low POD activity
as compare to control in potato at ambient temperature storage due to low
available oxygen required for the oxidation of phenols and peroxides. The
increased POD activity by the end of storage particularly in control might be
attributed to the physiological stress in the form of senescence and sprouting in
potato. The increased POD activity at senescence has also been reported by
different scientists in potato (Afify et al., 2012) mandarin (El-hilali et al., 2003),
Cherry (Tian et al., 2004) which confirms the observations presented in the
present study.
4.2.14 Effect on Chip Moisture Contents
Progressive increase in chip moisture contents (CMC) was recorded in
response to different packaging material during storage. Treatment means
showed maximum moisture contents in the chip processed from T1 followed by
T2 while, minimum moisture contents identified in T6. In general non significant
difference observed between all other packaging materials. Storage interval
means showed maximum CMC during the last week storage while during first
month storage the CMC remained statistically similar in all the treatments. The
119
interaction between treatments and storage revealed maximum chip moisture
contents in T1 at the end of storage time (Fig.14).
Chip moisture contents increased in all the treatments with the
progression in storage time however, the change was found more pronounced in
control as compare to packaged potatoes. The maximum percentage increase in
CMC in control till the end of storage was about 50% in control as compare to
21.5% and 23.5% in LDPE and PP packaged potato respectively. Generally
packagings retained lower chip moisture contents as compare to control till the
end of storage time.
Mass transfer during potato chips processing was associated with the
moisture loss and oil uptake during frying. The moisture contents diffused out of
the cellular matrix leaving behind capillary pores which were consequently filled
by oil (Mellema, 2003). The increase in fat and decrease in moisture contents
during frying has also been reported by Kita et al. (2004). High moisture contents
in potato chips are very critical since it cause sogginess and hydrolytic rancidity
due to free fatty acid formation during storage.
Frying has been described as immersion of food products in edible oil
heated at temperature above the boiling point of water (Hubbard and Farkas, 1999)
thus precisely termed as dehydration process. The initial moisture content in potato
chips before frying was around 74.50% with minor fat content (0.8% on dry
weight basis). After frying the Chip moisture contents decreased up to 1.24 %
while the fat contents increased by 30%. Potato with high specific gravity and dry
matter contents were reported to produce potato chips with low moisture contents
120
1
1.4
1.8
2.2
2.6
1 14 28 42 56 70
Storage intervals (day)
Ch
ip m
oist
ure
con
ten
ts (
%)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 14 Chip moisture contents in potato under different packagings showing highest increase in control during storage (LSD (0.05) for treatment = 0.03624 LSD (0.05) for interval = 0.03139 LSD (0.05) for interaction = 0.08877)
Vertical bars show ±SE of means.
121
(Pinthus et al., 1995). Although non significant difference observed in CMC
value in response to different packaging application but found effective in the
preparation of potato chips with lower moisture contents as compare to control.
In the present investigation, the packaged potatoes maintained high specific
gravity value during storage thus produced potato chips with low moisture
contents which also confirmed the previous findings reported by Mehta and
Swinburn (2001) and Aguilera et al. (2000).
4.2.15 Effect on Chip Fat Absorption
Chip fat absorption (CFA) increased with the increase in storage period in
all the treatments. Treatment means demonstrated maximum CFA in T1 and
minimum in T4 and T6, while non significant difference observed in most of the
other treatments. The storage interval means showed maximum CFA during the
end of storage period while minimum was found during the early weeks of
storage. The interaction between storage intervals and treatment means showed
maximum CFA during the last of storage in T1 followed by T3. The maximum
percentage increase in CFA was observed in control during the last month of
storage (Fig.15).
CFA increased in all the treatments during storage period and found
maximum in control and minimum in polyethylene (LDPE, MDPE and HDPE) and
polypropylene packaged potatoes. The percentage increase in control was around
33.88% in control as compare to 17.75%, 18.41% and 19.14% in LDPE, MDPE
and HDPE packagings respectively. The application of different packaging
materials retained low CFA as compare to control.
122
30
33
36
39
42
45
48
1 14 28 42 56 70
Storage intervals (day)
Ch
ip f
at a
bso
rpti
on (
%)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 15 Chip fat absorption in potato under different packagings showing maximum value in control during storage (LSD (0.05) for treatment = 0.4579 LSD (0.05) for interval = 0.1413 LSD (0.05) for interaction = 1.1220)
Vertical bars show ±SE of means.
123
Oil is the major source of flavor enhancer in potato chips but its high level
is of great concern for the producer and consumer for economic and food safety
point of view respectively. Oil absorption during frying in potato chips depends on
different factors like tuber specific gravity (Mehta and Swinburn, 2001), pre drying
(Pedreschi and Moyano, 2005), modification in size and thickness (Gamble and
Rice, 1988), frying temperature (Mellema, 2003), modification in frying
techniques (Mehta and Swinburn, 2001) and frying medium (Berry et al., 1999),
and potato chips coatings (Williams and Mittal 1999). Kita, (2002) reported that
potatoes with high specific gravity and starch contents produce chips with low oil
contents during frying. Potatoes stored in polyethylene and polypropylene
packaging retained high specific gravity and appreciable starch contents thus
produced chips with lower fat contents as compare to control. The inverse
proportion between tuber specific gravity and fat absorption has also been reported
by Hagenimana et al., (1998) which confirmed the present findings.
4.2.16 Effect on Chip Color
Chip Color (CCL) recorded in terms of approximate L-value showed steady
decrease with the increase in storage time. The treatments means illustrated
minimum CCL value in T1 and T3 while all other treatments were found
statistically similar (at α= 0.05). Storage interval means showed maximum CCL
values during the first month and minimum at the end of storage. The interaction
between treatments and storage intervals showed maximum CCL value during the
start of storage in all the treatments and minimum in T1 and T3 at the end of storage
period(Fig.16).
124
56
58
60
62
64
66
1 14 28 42 56 70
Storage intervals (day)
Ch
ip c
olor
(L
-val
ue)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 16 Chip color in potato under different packagings showing highest value in polypropylene during storage (LSD (0.05) for treatment = 1.0290 LSD (0.05) for interval = 0.3173 LSD (0.05) for interaction = 2.5200)
Vertical bars show ±SE of means.
125
Packaged potatoes expressed appreciable CCL value during the storage as compare
to control. CCL values obtained in LDPE (61.75) and MDPE (60.67) packaged
potato at the end of storage was similar to that recorded in control during 28th and
42nd days respectively. Maximum CCL value (62.00) was identified in
polypropylene packaged potatoes however remained statistically similar to the
most of other treatments at the end of storage.
Chip Color is the most important quality parameter sternly related to the
consumer perception for the product acceptance (Segnini et al., 1999). Potato chip
color is the consequence of Maillard reaction primarily related to the presence of
reducing sugars, protein, frying temperature and duration (Mackay et al., 1990). In
addition the CCL value is an important index of toxic acrylamide formation in
potato during high temperature processing (Stadler et al., 2002).
CCL values in the present investigation were quantified on the basis of
approximate L-values as described in fry color chart by British Potato Council
(BPC, UK). L* is the luminance having colorimeteric value ranges between 0
(Black) to 100 (Light) however the L-value for potato chips color presented in the
fry color chart ranged between 65 (Grade-I) to 49 (Grade-V). In general the CCL
values remained statistically similar in response to most of the packaging
applications however found minimum in control as compare to all other treatments.
Since the frying temperature and duration remained constant factors in potato
processing thus presence of reducing sugars being the major determinant of CCL
values during storage. Potato with low reducing sugar contents retained maximum
CCL value as happened in packaged potatoes during storage. The correlation
126
between reducing sugar contents and potato chip color has also been reported by
different researchers like De Wilde et al. (2004), Biedermann-Brem et al. (2003)
and Rodrigues- Saona and Wrolstad, (1997).
4.2.17 Effect on Chip Crispiness
Chip crispiness (CCR) scores showed a steady increase followed by final
decrease in all the treatments however the rate of decrease in CCR scores was
found lower in packaged potatoes as compare to control. Treatment means
revealed non significant difference in T4, T6, T7 and T8 while T2, T3 and T5 were
also found statistically similar at 5% level of significance. Storage interval means
showed initial increase in CCR scores which remained persistent during the most
of storage time and found minimum during the end of storage. The interaction
between treatments and storage intervals showed maximum CCR scores in T4 and
T8 on 42nd and 28th days respectively. Minimum CCR scores were identified in
control in T1 at the end of storage (Fig.17).
CCR scores expressed in T4 and T6 at the end of storage were found similar
to those identified on 28th day storage in control. Over all percentage decline in
CCR scores was found maximum (45.76%) in Control and minimum (16.14%) in
Poly propylene packaged potatoes during storage. Potato chip texture is often
described as crispiness which is an important sensorial attribute for consumer’s
appreciations. Eminent crispy structure develops in potato chip due to the
hardening of chip crust during frying at elevated temperature (Pedreschi et al.,
2001) Crispiness in potato chips is dependent on the excellence of raw material and
improved processing techniques. Potato tubers with high specific gravity and dry
127
2
2.5
3
3.5
4
4.5
5
1 14 28 42 56 70
Storage intervals (day)
Chip
cri
spin
ess
(sco
res)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 17 Chip Crispiness in potato under different packagings showing highest value in polypropylene and LDPE during storage (LSD(0.05) for treatment= 0.1788 LSD(0.05) for interval= 0.1548 LSD(0.05) for interaction= 0.4379)
Vertical bars show ±SE of means.
128
matter contents reported to produce potato chips with high crispiness value
predominantly influenced by starch and non starch polysaccharides (proto pectin)
contents (Kita, 2002). Jaswal, (1991) reported that the potato with high specific
gravity contain high molecular weight, stable and compact polysaccharides (starch,
pectin etc.) contents preventing their integrity thus contributing to their appreciable
textural configurations during frying. In the present study the potato tubers with
high specific gravity value maintained appreciable CCR scores in the fried
products. Although CCR scores with in most of packaging materials remained
statistically in significant however potatoes with high specific gravity value
produced chips with appreciable CCR value as compare to control which
confirmed the findings reported by the researchers above.
4.2.18 Effect on Chip Flavor
Chips flavor (CFL) estimated as scores recorded by the judges showed an
initial increase and eventual decreasing trend in all the treatments during the
storage. The treatment means exhibited maximum CFL scores recorded in T6, T7
and T4, non significant difference was recorded between T2 and T8 while
minimum CFL scores were identified in T1, T3 and T5. The means of storage
intervals showed maximum CFL during the mid storage intervals while minimum
were articulated during the start and end of the storage. The interaction between
storage intervals and treatments showed minimum (2.73/5.00) and maximum
(4.17/5.00) scores in T1 and T6 respectively during storage (Fig.18). In general
CFL scores increased in all the treatments after 28th days storage which started to
decline after 56th days storage in most of the treatments. Potatoes stored in
129
2.5
3
3.5
4
4.5
5
1 14 28 42 56 70
Storage intervals (day)
Ch
ip f
lavo
r (s
core
s)
Control
Jute
Nylon
Polypropylene
Cotton
LDPE
MDPE
HDPE
Fig. 18 Chip Flavor in potato under different packagings showing highest value in polypropylene during storage
(LSD (0.05) for treatment = 0.1480 LSD (0.05) for interval l= 0.0456 LSD (0.05) for interaction = 0.3624)
Vertical bars show ±SE of means.
130
polyethylene and polypropylene packaging retained appreciable CFL scores by the
end of storage period as compare to control.
Flavor is the sensory impression of food detected by the blend of taste and
smell senses. It is the over all resultant impression derived by the taste buds in
mouth and aroma detected by olfactory epithelium in nose. Flavor evolution in
potato chips is primarily attributed to the oil uptake and corresponding volatile
formations during thermal processing (Martin and Ames, 2001). In the present
study generally CFL scores were found in consistent with the other quality
attributes in potato chips. The maximum CFL scores were identified in LDPE,
MDPE and PP packaged potatoes as compare to control.
4.3 EFFECT OF DIFFERENT LIGHT SOURCES ON THE QUALITY
ATTRIBUTES OF POTATO
The objective of the second experiment of 2nd phase was to identify most
appropriate light source for best potato variety “Lady Rosetta” with appreciable
retention of different quality parameters. Potato tubers were placed for 27 days at
ambient storage (25± 3oC) under different light sources i.e. blue, fluorescent,
green, mercury and red along with dark storage which also served as normal
control. Physico-chemical, functional and processing attributes were studied in
potato tubers and potato chips at three and seven days interval respectively.
4.3.1 Effect on Weight Loss (%)
In response to different light sources weight loss (%) increased in all the
treatment with time however maximum weight loss (%) was reported in T2 and
minimum in T6 at the end of storage. Treatment means showed minimum weight
131
loss (%) in T6 followed by T3 and T4 which were found statistically similar.
Maximum weight loss was recorded in T2 followed by T5 and T1 which were also
found statistically at par. Interaction between treatments and storage intervals
showed maximum weight loss (%) in all the treatments at the end of storage time
except in control (Fig.19).
In general non significant difference was observed with in the treatments by
the mid storage period, which was trailed by significant increase under fluorescent
light (2.958%), blue light (2.908%) and red light (2.918%) till the end of trial.
Steady increase in weight loss was found under mercury (2.450%) and green
(2.474%) light exposures with minimum increase recorded in tubers placed under
dark (2.276%). Gachango et al. (2008) reported minimum weight loss in potato
stored in dark as compare to those placed under indirect sunlight and direct
illuminations. Kabira and Lemaga (2003) anticipated the use of dark rooms for
potatoes to decrease the eventual weight loss during storage.
International Potato centre (CIP, 1997) proposed the storage of potato
under indirect sunlight for maintaining tuber quality. Walingo et al. (1995) also
reported lower weight loss in potato under dark as compare to different light
sources. In the present study significant weight loss (%) in potatoes under
fluorescent, blue and red lights might be attributed to their high level of energy
resulted in the elevated rate of respiration and eventual increased weight loss (%)
as compare to dark and other light sources which was found in line with the
findings of the researchers reported above.
132
0
0.5
1
1.5
2
2.5
3
3.5
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
Wei
ght
loss
(%
)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 19 Weight loss in potato under different light sources showing minimum loss in dark followed by mercury during storage (LSD (0.05) for treatment = 0.01617 LSD (0.05) for interval = 0.02087 LSD (0.05) for interaction = 0.05112)
Vertical bars show ±SE of means.
133
4.3.2 Effect on Total Soluble Solids
Steady increase in the total soluble solids (TSS) observed in all the
treatments under different light illuminations. The treatment means showed close
statistical similarities between different light exposures. Least increase was
observed in Dark storage while maximum TSS accumulation was observed in T2
and T5 which were found statistically similar. Moderate TSS increase was found in
T3 and T4 which were statistically similar (α-0.05) during storage. The storage
interval means revealed non significant difference between the treatments during
the 1st week and found significant at the end of storage (Fig. 20).
Highest TSS accumulation was noticed in potato placed under red light
(5.98 obrix) and flourescent light (5.97 obrix) followed by Blue light (5.96 obrix).
TSS accumulation remained statistically similar in green light, mercury light and
dark at the end of storage. The percentage increase in TSS during the trial
remained maximum (6.20%) under fluorescent light as compare to minimum
(3.95%) in dark and green light storage.
The increase in TSS is attributed to the hydrolytic conversion of insoluble
starch in to soluble sugars during storage (Kittur et al., 2001). Exposure of tubers
to high energy illuminations (flourescent, blue and red) may cause increase in
starch hydrolysis due to physiological stress eventually increased the total soluble
contents as compare to other storage conditions. Nema et al. (2008) reported
elevated level of soluble sugars due to tuber stress and exposure to different high
energy light sources, this elevated level of reducing sugars particularly in the form
of galactose served as precursor for alkaloids formation (Percival et al., 1993). In
the present study exposure of potato tubers to high energy lights caused increased
134
5.5
5.6
5.7
5.8
5.9
6
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
Tot
al s
olu
ble
sol
ids
( oB
rix)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 20 Total soluble solids in potato under different light sources showing lowest increase in dark and green light during storage (LSD (0.05) for treatment = 0.005112 LSD (0.05) for interval = 0.002357 LSD (0.05) for interaction = 0.005774)
Vertical bars show ±SE of means.
135
starch degradation and favored the formation of soluble sugars and retained higher
TSS accumulation as compare to dark which corresponded the finding of
researchers reported above.
4.3.3 Effect on Color
Highly significant decrease in color scores was observed under different
light sources as compare to dark storage. The treatment means showed significant
difference between color scores in response to different illuminations. Minimum
color scores were reported in T2 followed by T1 and T5 while maximum scores
were observed in T6. The storage interval means revealed significant difference
with maximum color scores reported during the start of trial and minimum at the
end of storage. The interaction between treatment means and storage intervals
showed appreciable color scores during the start of experiment in all the treatments
and started to decline after 1st week storage except in T6 (Fig.21).
Potato placed under dark storage retained maximum color scores through
out the storage, color scores retained by dark storage at the end of storage were
found greater than those tubers placed under fluorescent light on 3rd day of
continuous illumination. In general color scores remained unaffected under dark
storage during the complete research trial and percentage decrease was only around
4% in contrast to 77% decrease in fluorescent illumination. Amongst different
treatments green and mercury illuminations maintained appreciable color scores
where the percentage decrease was found 21% to 29% respectively. Storage of
tubers under blue and red illuminations also presented poor color scores i.e.
2.83/8.00 and 3.00/8.00 respectively by the end of storage period.
136
1.5
2.5
3.5
4.5
5.5
6.5
7.5
8.5
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
Col
or (
scal
e)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 21 Color in potato under different light sources showing highest scores in dark during storage (LSD (0.05) for treatment = 0.0503 LSD (0.05) for interval = 0.1819 LSD (0.05) for interaction = 0.4457)
137
Estimation of color scores in potato tuber in response to different light sources was
carried out with the help of scale designed by Grunenfelder et al. (2006) for Dark
Red Norland variety with inverse modification (8 = Normal, 1 = Greened). The
discoloration in potato tuber in response to different light sources is primarily
associated with the chlorophyll formation in periderm (Pavlista, 2001). Percival,
(1999) reported increase in chlorophyll contents in potato tubers in response to
different light sources and found maximum chlorophyll accumulation in
fluorescent and minimum in mercury illuminations. Edward and Cobb, (1997)
stated that the rate of chlorophyll synthesis in potato tuber is highly effected by the
light exposure. Griffith et al. (1994) reported dark green patches in potato tuber
due to stress imposed by sunlight. In the present investigation the substantial
retention of high color scores in tuber stored in dark as compare to different
illumination confirmed the finding of researchers reported above.
4.3.4 Effect on Glucose
The general trend was an increase in glucose contents in all treatments
during the storage which remained steady under dark storage. The treatments
means exhibited maximum increase in T2 and T5 and were found at par statistically.
Significant increase in glucose contents were also recorded in T2. Minimum
glucose retention was demonstrated in T6 followed by T3 and T4. Storage interval
means showed minimum glucose contents at the start and maximum at the end of
storage period. Interaction between treatments and storage intervals revealed
significant increase in glucose contents during the last week of storage in T1, T2
and T5 (Fig. 22).
138
0
30
60
90
120
150
180
210
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
Glu
cose
(m
g/10
0g)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 22 Glucose in potato under different light sources showing highest increase in florescent light during storage
(LSD (0.05) for treatment = 1.477 LSD (0.05) for interval = 1.906 LSD (0.05) for interaction = 4.670)
Vertical bars show ±SE of means.
139
Increase in glucose contents in tubers started from the start of storage in blue,
fluorescent and red illuminations and remained two folds than the rest of
treatments by the end of 3rd week. Green and mercury light retained moderate
increase in glucose contents and were found statistically insignificant during most
of the storage period. Glucose contents recorded at the end of storage in dark were
found lower than that recorded in fluorescent and red lights by the end of 2nd week
and found minimum through out the storage period. The glucose contents
accumulation in potato tubers is associated with the starch hydrolysis during the
storage period (Sonnewald 2001) and accelerated during tuber stress due to
exposure to high energy illuminations (Percival, 1993). The greater increase in
glucose contents during storage under fluorescent, red and blue lights as compare
to other treatments might be due to the increased relative degradation of starch
contents. The results were also in close confirmation with the findings of Chen and
Setter (2003) who reported decreased glucose contents in potato tubers under shade
storage.
4.3.5 Effect on Total Sugar
Total sugar accumulation in potato tubers in response to different
illuminations was increased constantly during storage and found in consistent with
the trend achieved in glucose contents (Fig 23). The treatment means showed
maximum sugar accumulation in T2 followed by T1 and T5 which were found
statistically same (α-0.05). Storage interval means showed non significant increase
in sugar content during 1st week followed by prominent increase during the rest of
storage period. Interaction between treatments and storage intervals showed
maximum sugar accumulation in T2 while minimum estimated in T6 at the end of
trial (Fig. 23).
140
800
840
880
920
960
1000
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
Tot
al s
uga
rs (
mg/
100g
)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 23 Total Sugar in potato under different light sources showing highest increase in florescent light during storage (LSD (0.05) for treatment = 2.602 LSD (0.05) for interval = 3.359 LSD (0.05) for interaction = 8.229)
Vertical bars show ±SE of means.
141
Total sugars increased under all illuminations and found minimum in tubers
stored under dark. The increase in sugar was highly significant under fluorescent, blue
and red lights with steady increase also observed under mercury and green light.
Storage under dark by the end of storage period retained lower sugar contents than that
estimated in fluorescent, blue and red lights by the end of 1st week storage. In terms of
their sugar accumulation blue and red illumination were found statistically same
during most of the storage period.
Continuous exposure of potato tubers to different light sources caused sugar
accumulation due to starch hydrolysis mediated through tuber stress (Percival, 1999).
The initial increase in sugar contents in response to different illuminations during
storage has also been reported by Olson (1996). Dale et al. (1993) reported elevated
sugar contents in potato exposed to continuous illumination as compare to those
placed under dark. The moderate sugar contents identified in green and mercury lights
might be due to lesser starch hydrolysis owing to their low energy spectrums which
has also been confirmed by Nema et al. (2008).
4.3.6 Effect on Starch
Data related to starch contents in response to different illumination revealed
non significant initial increase followed by progressive decline with the storage period.
The treatment means showed minimum starch contents in T1, T2 and T5 and were
found statistically similar at 5% level of significance. T6 retained maximum starch
contents at the end of storage followed by T3 and T4 which were also found at par
statistically. The storage interval means showed maximum starch content during 1st
week storage and than declined significantly by the end of storage period. The
interaction between treatments and storage intervals showed minimum starch contents
in T1, T2 and T5 on last day storage (Fig. 24).
142
17.5
18
18.5
19
19.5
20
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
Sta
rch (%
)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 24 Starch in potato under different light sources showing highest decline in florescent and red light during storage (LSD (0.05) for treatment = 0.0996 LSD (0.05) for interval = 0.1287 LSD (0.05) for interaction = 0.3151)
Vertical bars show ±SE of means.
143
In general after an initial increase all the treatments experienced starch depletion in
response to different illuminations however the percentage decrease was highly
prominent in blue (8.75%), fluorescent (9.0%) and red (8.86%) lights as compare
to other treatments. The minimum percentage decline in starch contents were
reported in dark (5.80%) followed by green (6.25%) and mercury (7.0%)
illuminations.
The initial increase in starch contents might be due to tendency of freshly
cure potato to accumulate dry matter primarily in form of starch (Kaul et al.,
2010). The metabolism of carbohydrate contents during post harvest storage is
very important both in table and processing potato varieties (Herrman et al., 1996).
The quality of potato tubers keep on changing due to depletion of starch and
formation of corresponding sugars during storage (Nourian et al., 2003). Nema et
al. (2008) reported that continuous exposure of tuber to high energy wavelengths
cause physiological stress characterized by increased rate of respiration followed
by starch depletion. Maximum starch depletion in potato under different high
energy illuminations (fluorescent, blue and red) during the present study confirmed
the findings reported above. General decline in starch content in different
treatments might be attributed to the consumption of respiratory substrate (starch)
during post harvest storage.
4.3.7 Effect on Ascorbic Acid
General trend showed reduction in ascorbic acid (AA) contents in response
to different illuminations during the storage time. The treatment means showed
significant difference amongst all with maximum and minimum AA retention in T6
144
and T2 respectively. The storage interval means showed significant difference in
AA contents with maximum retention at the start and minimum recorded at the end
of trial. The interaction between treatments and storage intervals showed
appreciable retention of AA in T6 followed by T3 during most of the storage
period. Significant reduction in AA contents was observed in T2 with in three days
illumination (Fig. 25).
In the present study exposure of potato tubers to different illuminations
caused significant reduction in AA. The reduction was highly significant in T2
where the percentage decline was around 10% with in three days which escalated
up to 29% by the end of one month storage. Exposure of tubers to blue and red
lights presented 23.5% and 25% decline in AA contents respectively. Moderate
reduction of AA contents also reported in case of green (17.2%) and mercury
(19.6%) illuminations. Dark storage of potato retained maximum AA contents and
percentage decline was observed around 11.8 % only. Ascorbic acid is considered
as important dietary antioxidant vitamin and known to decline during post harvest
storage period in fruits and vegetables (Lee and Kader 2000) due to oxidation (Piga
et al., 2003), photo degradation (Leskova et al., 2006) or utilization as respiratory
substrate (Kader, 2002). Owing to its high degree of sensitivity it is considered as
an imperative index of quality in fruits and vegetable during storage and food
processing (Ozkan et al., 2004). Dale et al. (2003) reported that ascorbic acid
contents decrease in horticultural produce due to light exposure, heat; low relative
humidity and prolonged storage time hence are critical considerations in
optimizing suitable post harvest storage conditions. Similar results
145
16
18
20
22
24
26
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
Asc
orbic
aci
d (m
g/10
0g)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 25 Ascorbic acid in potato under different light sources showing highest retention in dark followed by green light during storage (LSD (0.05) for treatment = 0.1696 LSD (0.05) for interval = 0.2189 LSD (0.05) for interaction = 0.5362)
Vertical bars show ±SE of means.
146
were reported in the present study by maximum retention of ascorbic acid in dark
storage as compare to different illuminations.
4.3.8 Effect on Chlorophyll
Chlorophyll contents continue to increase significantly during the storage
time in response to different light exposures (Fig. 26). The treatments means
showed maximum chlorophyll accumulation in T2 followed by T5 and T1 which
were found statistically similar (α-0.05). Considerable chlorophyll contents were
estimated in T5 followed by restrained contents identified in T3 and T4 which were
found statistically at par (α-0.05). Chlorophyll contents remained at minimum level
in T6. The interaction between treatments and storage intervals demonstrated
minimum contents witnessed in most of the treatments by the end of 1st week
storage while maximum were estimated in T1, T2 and T5 by the end of last week
(Fig. 26).
Chlorophyll contents increased progressively under fluorescent, blue and
red illuminations and showed steady increase under dark during the storage period.
The contents started to increase in high energy illuminations with in 1st week of
storage particularly in fluorescent light where the percentage increase was 53.0%
more than that identified in dark at the end of storage (45.4%).
Maximum contents were recorded in T2 (3.64 mg/100g) with significant
linear increase in the chlorophyll contents i.e. more than six folds over the
complete storage period. Response of potato in exposure to red (2.99 mg/100g) and
blue (2.88 mg/100g) illuminations accumulated considerable chlorophyll contents
as compare to mercury (1.99 mg/100g) and green (1.66 mg/100g)
147
0
0.5
1
1.5
2
2.5
3
3.5
4
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
Chl
orop
hyl
l (m
g/10
0g d
.w)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 26 Chlorophyll in potato under different light sources showing maximum increase in florescent and blue lights during storage (LSD (0.05) for treatment = 0.1617 LSD (0.05) for interval= 0.2087 LSD (0.05) for interaction = 0.5112)
Vertical bars show ±SE of means.
148
lights at the end of storage. In general all different kind of illuminations caused
increase in chlorophyll contents at erratic pace with no indication of termination
during the complete trail.
Exposure of potato tubers in response to light caused the formation of
chlorophyll in cortical parenchyma due to conversion of amyloplast in to
chloroplast (Pavlista, 2001).The extent of greening in retail outlets emphasizing the
development and realization of appropriate light source to maintain desirable
quality attributes in potato tubers. Percival, (1999) compared the response of
different tuber varieties to various light sources and reported irrespective of variety
maximum chlorophyll accumulation under fluorescent and sodium illuminations as
compare to mercury light and dark. Grunenfelder et al., (2006) exposed different
colored potato varieties to fluorescent lighting of similar intensity and found
discoloration of periderm in all of them due to significant increase in chlorophyll
contents. The present study demonstrated significant chlorophyll accumulation in
potato tubers due to various illuminations. Our results concluded that the
replacement of fluorescent light with green or mercury illuminations in retail
displays for time being might cause reduction in potato greening as also reported
by researchers above. Dark potato storage demonstrated appreciable tuber quality
due to minimum chlorophyll accumulation thus might be recommended for
prolonged tuber storage which has also been concluded by different researchers
like Nema et al. (2008) Rita et al. (2007) and Edward and Cobb (1997).
4.3.9 Effect on Total Glycoalkaloids
Data related to Total Glycoalkaloids (TGA) showed progressive increase
under different illuminations during storage. The treatments means showed
149
significant difference between their TGA contents with maximum retention in T2
followed by T1 and T5 while minimum TGA contents were identified in T6. The
storage interval means showed minimum TGA contents during 1st week and than
progressively increased till the end of storage. Significant interaction was observed
between treatments and storage intervals with highest TGA contents estimated in
T2 during last week while least were identified in all treatment by 1st week storage
(Fig. 27).
The TGA contents increased through out the storage period irrespective of
treatments however the rate of increase in TGA contents was higher in fluorescent,
blue and red light illuminations. The increase in TGA contents under fluorescent
light was maximum (79.92 mg/100g d.w) and estimated around 8-folds as compare
to 2.5-folds increase in dark by the end of storage period. The increase in TGA
contents under fluorescent illumination at the end of storage surpassed the safe
limits described for human intake i.e 20mg /100g f.w (Mensinga et al., 2005). In
general percentage increase in TGA with in different storage interval was found
highest in last week. Minimum TGA accumulation was identified in dark (18.90
mg/100g d.w) followed by mercury (28.03 mg/100g d.w) and green (30.93
mg/100g d.w) illuminations.
TGA contents estimated in the present study in terms of solanine equivalent
are affected by different illuminations and also associated with the elevated
chlorophyll contents. Grunenfelder et al. (2006) studied the increase in TGA and
150
0
15
30
45
60
75
90
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
TG
A (m
g/10
0g d
.w)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 27 Total glycoalkaloids in potato under different light sources showing highest increase in florescent light during storage (LSD (0.05) for treatment = 0.4137 LSD (0.05) for interval = 0.5341 LSD (0.05) for interaction = 1.3080)
Vertical bars show ±SE of means.
151
chlorophyll contents under fluorescent light and concluded parallel but
independent development of both compounds. Rita et al. (2007) compared TGA
accumulation in potato tubers under different illuminations during postharvest
storage. He found maximum and minimum TGA contents under fluorescent light
and dark respectively. Percival et al. (1999) investigated light-induced TGA
accumulation in potato tubers under four different illuminations. He declared
maximum contents under fluorescent and sodium lights and minimum under dark.
Our results in the present study also confirmed the pervious finding as steady TGA
contents in dark as compare to significant increase under fluorescent light. The trial
also exhibited parallel association between chlorophyll and glycoalkaloids
accumulations in potato tubers. The process is however found independent due to
increased TGA contents in blue to red and green to mercury lights having less
corresponding chlorophyll contents during the same storage period.
4.3.10 Effect on Total Phenolic Contents
Total phenolic contents (TPC) increased steadily during the storage period
in response to different illuminations however the increased is followed by
considerable decline in T1, T2 and T5.In general non significant difference in
treatment means was observed except in T4 and T6. The storage interval means
however showed significant difference with maximum and minimum TPC
identified in the end and start of experiment. Highly significant interaction was
observed between treatments and storage intervals after the mid storage period
(Fig. 28).
Total phenolic contents increased during the start of storage in all the
treatments and the initial rise was found independent of different illuminations. I
152
110
120
130
140
150
160
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
TPC
(m
g G
AE
/100
g d.w
)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 28 Total phenolic contents in potato under different light sources showing maximum retention in green light during storage (LSD (0.05) for treatment = 0.5211 LSD (0.05) for interval = 0.6727 LSD (0.05) for interaction = 1.6480)
Vertical bars show ±SE of means.
153
general non significant difference was observed in most of the treatments till 9th
day storage. TPC contents significantly increased in all the treatments by the end
of 2nd week storage which was followed by progressive decline in fluorescent, blue
and red illuminations during the last week of storage. TPC increased continuously
under green, mercury and dark storage with no sign of cessation during the storage
period, however the rate of TPC increase during the 1st half of storage was found
slower as compare to high energy illuminations (T1, T2 and T5).
Total phenolic contents showed varied retention under different
illuminations during storage period. Light is considered as an important factor
causing the biosynthesis of phenolic compounds facilitated by the activity of
phenylalanine ammonia-lyase enzymes (Lewis et al.,1998) In addition it is also
known to initiate the anthocyanin and chlorogenic biosynthesis pathways
contributing to the total phenolic contents in potato tubers (Griffiths, 1995). The
swift initial increase in TPC under different light sources and steady TPC under
dark partially confirmed the findings reported by different researchers above and
negated the investigation reported by Reyes and Zevallos, (2003) who reported no
considerable effect of light on the TPC accumulation in purple-fleshed potato
tubers. The possible reason might be due to the varietal difference and lack of
comparative study under different illuminations. Tubers placed under green and
mercury lights retained appreciable TPC at the end of storage probably due to lack
of tuber stress and moderate respiration rate. The decline in TPC contents under
high energy illumination at the end of storage might be attributed to the tuber stress
due to high metabolic rate, increased rate of respiration causing eventual decline in
total phenolic contents.
154
4.3.11 Effect on Radical Scavenging Activity
Radical scavenging activity (RSA) estimated in terms of % inhibition
of DPPH showed slight initial increase followed by gradual decrease under
all illuminations except in dark. Treatment means showed T6 maintained
maximum activity followed by T3, T4 and T5 while T2 showed minimum
RSA activity followed by T1. Storage interval means showed maximum
activity till 2nd week and than steadily declined till the end. The RSA
activities at the start and end of trial was found statistically (α-0.05) similar.
Interaction between treatments and storage intervals was initially found less
significant and than become highly significantly by the end of storage
period. The maximum activity was expressed in T3 and T6 during 3rd and 2nd
week storages respectively (Fig. 29).
In general RSA activity exhibited initial increase till mid storage
period and finally declined forming a sort of parabolic curve. However the
rate of increase and decrease in activity was considerably affected by
different illuminations. Radical scavenging activity increased during first
week and attained maximum by second week in T1 (45.43%), T2 (45.80%)
and T5 (47.57%) followed by progressive decline afterward. The trend
remained same at variable pace in T3 (48.73%), T4 (47.33%) and T5
(49.47%) where they showed maximum activity by the end of 3rd week
followed by steady decline. It is eventually observed that except in potato
tubers in dark storage all other placed under different illuminations lost
considerable activity below or close to their initial rate expressed before the
start of trial.
155
25
30
35
40
45
50
55
1 3 6 9 12 15 18 21 24 27
Storage intervals (day)
RSA
(%
)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 29 Radical scavenging activity in potato under different light sources showing highest activity in dark during storage (LSD (0.05) for treatment = 0.2980 LSD (0.05) for interval = 0.3854 LSD (0.05) for interaction = 0.9440)
Vertical bars show ±SE of means.
156
RSA activity corresponds to the antioxidant potential retained by the
potato tubers and is associated with the presence of different functional
components like phenolic compounds, carotenoids, ascorbic acid and
tocopherols (Shahidi, 2002). In the present study storage under different
illuminations conferred diverse affects on these antioxidant components as
attributed to the parallel accumulation of phenolics and depletion of ascorbic
acids. The prolonged exposure of potato tubers to high energy illuminations
might bestow tuber stress consequently resulted in the loss of phenolic
substrate due to increased polyphenol oxidase activity (Bryant, 2004). The
significant retention of RSA activity at the end of storage under dark as
compare to different illuminations might be due to the appreciable retention
of dietary antioxidant like ascorbic acid, phenolics etc. The significant
correlation between RSA activity and these functional components has also
been reported by Hejtmankova, et al. (2009), Lachmann et al. (2008) and Kalt et
al. (2001).
4.3.12 Effect on Chips Moisture Contents
Increase in Chips moisture contents (CMC) was observed under all
illuminations including the dark storage. The treatment means showed non
significant difference between T1, T2, T5 and T3, T4, T6, however significant
difference exhibited between all the storage interval means. The interaction
between treatment and storage intervals was found significant with
maximum and minimum CMC recorded during the end and start of the
storage respectively (Fig. 30).
157
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1 7 14 21 28
Storage intervals (day)
Chip
moi
sture
con
tents
(%
)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 30 Chip moisture contents in potato under different light sources showing lowest in dark during storage (LSD (0.05) for treatment = 0.00730 LSD (0.05) for interval = 0.00666 LSD (0.05) for interaction = 0.01633)
Vertical bars show ±SE of means.
158
Maximum CMC was recorded in potato stored under red (1.44%)
light followed by fluorescent (1.43%) and blue (1.42%) illuminations at the
end of storage. The increase in CMC during these treatments remained
statistically similar through out their storage interval. Minimum CMC was
estimated in dark (1.37%) followed by green (1.38%) and mercury (1.40%)
illuminations. The increase in CMC amongst these treatments remained
statistically at par during most of the storage time.
The response of different illuminations on CMC segregated into two
distinct groups having non significant difference recorded between their
treatment means. 1st group exposed to high energy lights maintained
relatively high CMC included potato exposed to blue, fluorescent and red
illuminations while the 2nd group with relatively low CMC retained potato
stored in green, mercury and dark storage. CMC in different potato chips
remained unaffected by different illuminations within the group. The
exposure of tubers under high energy lights might cause tuber stress
followed by starch degradation consequently produced potato chips with
high moisture contents (Aguilera et al. 2000) as compare to those stored under
low energy illuminations and dark storage. Potato stored under dark retained
appreciable specific gravity contents due to intact starch molecules thus produced
chips with low moisture contents. The results presented are in agreement with the
findings of Mehta and Swinburn (2001) and pinthus et al. (1995) who reported
low CMC in potato chips processed from tubers with low specific gravity and
starch contents.
159
4.3.13 Effect on Chip Fat Absorption
Chip fat absorption (CFA) increased with the advancement in storage
period under different illuminations and dark. Treatment means demonstrated
maximum CFA in T2 with non significant difference recorded with T5. T6
retained minimum CFA however found statistically at par with T1, T3 and T4. The
storage interval means showed highest CFA during the end of storage period
while lowest was estimated at the start of storage. The interaction between
storage intervals and treatment means showed maximum CFA at the end of
storage in T2 with non significant difference recorded amongst all other
treatments (Fig. 31).
CFA increased in all the treatments during storage period and found
maximum in potato placed under fluorescent light (33.10%) and minimum in dark
(30.87%) storage. The data showed no significant effect on CFA in response to all
other illuminations at the end of trial. Our results showed low fat absorption in
potato with high starch contents during storage under different illuminations. Such
inverse relationship confirmed the previous findings reported by Kita (2002),
Mehta and Swinburn (2001) and Hagenimana et al. (1998).
4.3.14 Effect on Chip Color
Chip Color (CCL) estimated in terms of approximate L- value showed
steady decrease with the increase in storage time under different illuminations. The
treatments means illustrated minimum CCL value in T2 and T5 while non
significant difference was recorded between T1 and T4. Maximum CCL values
were recorded in T6 and T3 which were found at par
160
29.5
30.3
31.1
31.9
32.7
33.5
1 7 14 21 28
Storage intervals (day)
Chip
fat
abso
rption
(%
)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 31 Chip fat absorption in potato under different light sources showing lowest value in dark during storage (LSD (0.05) for treatment = 0.2310 LSD (0.05) for interval = 0.2108 LSD (0.05) for interaction = 0.5165)
Vertical bars show ±SE of means.
161
statistically (α-0.05). Storage interval means showed maximum CCL values by the
mid of storage time while minimum was recorded at the end of storage. The
interaction between treatments and storage intervals showed maximum CCL value
during the most of storage period however maximum CCL values were estimated
in T6 and T3 at the end of storage (Fig. 32).
Potatoes placed under dark retained appreciable CCL value during the
storage as compare to those placed under different illuminations. Maximum CCL
value (64.00) was identified in potatoes placed under dark however remained
statistically similar to those placed under green light while minimum CCL value
(59.33) was estimated in fluorescent illumination.
Chip Color is the most important quality parameter sternly related to the
consumer insight for the product acceptance (Segnini et al., 1999) and considered
as an important index of toxic acrylamide formation in potato during high
temperature processing (Stadler et al., 2002). Chip color is affected by chlorophyll
development and sugar accumulation during different illuminations. Since the
frying temperature and duration remained constant factors in during processing the
appearance of chlorophyll and advent of reducing sugars being the major
determinant of CCL values in the present trial. Potato with low reducing sugar
contents retained maximum CCL value as happened in those stored under dark.
The correlation between reducing sugar contents and potato chip color has also
been reported by different researchers like De Wilde et al. (2004) and Rodrigues-
Saona and Wrolstad, (1997).
162
58
60
62
64
66
1 7 14 21 28
Storage intervals (day)
Chip
col
or (L
-val
ue)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 32 Chip color in potato under different light sources showing highest value in dark and green light during storage (LSD (0.05) for treatment = 0.9399 LSD (0.05) for interval = 0.8580 LSD (0.05) for interaction = 2.1020)
Vertical bars show ±SE of means.
163
4.3.15 Effect on Chip Crispiness
Chip crispiness (CCR) scores showed a steady increase followed by final
decrease in all the treatments however the rate of decrease in CCR scores was
found maximum in potato exposed to fluorescent packaging and minimum under
dark storage. Treatment means revealed non significant difference between T3, T4
and T6, while T1, T2 and T5 were also found statistically similar at 5% level of
significance. Storage interval means showed initial increase in CCR scores which
remained maximal at the mid storage followed by decline in all treatments. The
interaction between treatments and storage intervals showed maximum CCR scores
in all treatments with non significant difference between them at mid storage
period. The interaction remained non significant with in most of the storage
intervals during the trial (Fig. 33). CCR scores expressed in T6 at the end of
storage were found similar to those identified on 3rd day storage in T1. Over all
percentage decline in CCR scores after attaining terminal value was found
maximum (16.7%) in T2 and minimum (8.7%) in potatoes under dark storage.
Crispiness in potato chips is dependent on the quality of raw material and
improved processing techniques. Potato tubers with high specific gravity and dry
matter contents reported to produce potato chips with high crispiness value
predominantly influenced by starch and non starch polysaccharides (proto pectin)
contents (Kita, 2002). Jaswal, (1991) reported that the potato with high specific
gravity contain high molecular weight, stable and compact polysaccharides (starch,
pectin etc.) contents preventing their integrity thus contributing to their appreciable
textural configurations during frying. In the present study the potato tubers with
164
3.5
4
4.5
5
1 7 14 21 28Storage intervals (day)
Chip
cri
spin
ess
(sco
res)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 33 Chip crispiness in potato under different light sources showing highest scores in dark and green light during storage (LSD (0.05) for treatment = 0.1424 LSD (0.05) for interval = 0.1300 LSD (0.05) for interaction = 0.3184)
165
high specific gravity value maintained appreciable CCR scores in the fried
products. Although CCR scores with in different illuminations remained
statistically in significant however potatoes with high specific gravity value as
those placed under dark storage produced chips with appreciable CCR value as
compare to those placed under different high energy illuminations which
confirmed the findings reported by the researchers above.
4.3.16 Effect on Chip Flavor
Chips flavor (CFL) estimated as scores recorded by the judges showed an
initial increase and eventual decreasing trend in all the treatments during the
storage. The treatment means exhibited maximum CFL scores recorded in T6
followed by T3, while non significant difference was identified between T1 and T4.
Lowest CFL scores were estimated in T2 followed by T5. Storage interval means
showed maximum CFL during D3 and D4 which were found statistically similar
while minimum scores were expressed at the start of experiment. The interaction
between storage intervals and treatments was significant with minimum CFL
estimated during 1st week storage and maximum estimated in T6 at mid storage
onwards till the end of storage (Fig. 34). In general CFL scores increased initially
under different illuminations followed by decline which was found highly
significant under fluorescent light. Steady decline in CFL scores observed in
potatoes stored under green and mercury illuminations. Over all dark potato
storage retained substantial CFL scores through out the storage period. Flavor
evolution in potato chips is primarily attributed to the oil uptake and corresponding
volatile formations during thermal processing (Warner et al., 1997).
166
3
3.5
4
4.5
5
1 7 14 21 28
Storage intervals (day)
Chip
fla
vor
(sco
res)
Blue
Florescent
Green
Mercury
Red
Dark
Fig. 34 Chip flavor in potato under different light sources showing highest scores in dark and green light during storage (LSD (0.05) for treatment = 0.1649 LSD (0.05) for interval = 0.1506 LSD (0.05) for interaction = 0.3688)
Vertical bars show ±SE of means.
167
In the present study generally CFL scores were found in consistent with the other
sensorial attributes in potato chips. The maximum CFL scores were identified in
dark storage potatoes as compare to those placed under different illuminations.
Lowest flavor scores in potato placed under fluorescent illumination might be due
to the bitter taste conferred by elevated glycoalkaloids contents produced during
storage which has also been previously reported by Mensinga et al. (2005).
4.4 EFFECT OF DIFFERENT TEMPERATURE STORAGE ON THE
QUALITY ATTRIBUTES OF POTATO
Potatoes are usually stored under low temperature for sprout prevention and
to ensure their continuous supply when ever needed. In the third experiment of 2nd
phase of study, post harvest storage stability of potato variety “Lady Rosetta” were
studied under different temperature regimes. The tubers were placed under 5oC,
15oC and 25oC temperatures storage and physico-chemical, functional and
processing attributes were studied at fourteen days interval.
4.4.1 Effect on weight Loss (%)
General trend was increase in weight loss (%) under all temperatures
storage; however the rate of increase was slower in T1 as compare to T2 and T3.
Treatment means showed significant difference between them with maximum
weight loss (%) estimated in T3 and minimum in T1. Data on weight loss revealed
significant differences between all the storage means with highest recorded on 84rth
day. Significant interaction was observed between treatments and storage intervals
with maximum weight loss (%) estimated in T3 after two month storage (Fig. 35).
168
0
3
6
9
12
15
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Wei
ght lo
ss (%
)
5°C
15°C
25°C
Fig. 35 Weight loss in potato under comparative temperature storage showing minimum loss at 5oC (LSD (0.05) for treatment = 0.06734 LSD (0.05) for days interval = 0.12290 LSD (0.05) for interaction = 0.2129)
Vertical bars show ±SE of means.
169
Amongst all temperature storage weight loss (%) increased with storage
period however remained under desirable limit during 1st month. Storage under
5oC and 15 oC expressed minimum weight loss (%) with non significant difference
recorded between them till 42nd day storage. Considerable weight loss (%) was
estimated at 25 oC on 42nd day storage which was similar to that recorded at 15 oC
on 112th day storage. Minimum weight loss estimated in T1 (3.25%) followed by T2
(8.29%) and T3 (13.29%) at their respective ends on 126th, 126th and 84rth days
storage. Overall highest weight loss (%) estimated in 25oC and not recorded after
84rth day storage due to shriveling and excessive sprouting rendering tuber
commercially unacceptable for the industrial processing.
Low temperature storage is an important technique in maintaining post
harvest quality of horticultural commodities however, it is essential to maintain
intact quality parameters and prevent them from low temperature disorders like
cold sweetening, chilling injury etc. Low temperature storage prevent sprouting in
potato by prolonging natural dormancy through imposed dormancy however the
critical temperature must be identified to prevent low temperature sweetening.
Weight loss (%) during post harvest storage of potato is attributed to moisture loss
due to evapotranspiration and dry matter loss due to respiration and sprouting
(Tester et al., 2005). Raghami (2009) reported direct relationship between storage
temperature and weight loss (%) in potato tubers. Ghazavi and Houshmand (2010)
studied respiration rate and weight loss (%) at different storage temperatures (5oC,
10oC and 15oC). The result indicated that the respiration rate and weight loss (%)
was found minimum at 5oC than other two temperature regimes. Amongst different
temperature storage, minimum weight loss (%) estimated at 5oC due to reduced
170
respiration rate which confirmed the findings of the researchers reported above.
The decreased weight loss under low temperature storage has also been reported by
different researchers in other horticultural commodities like Potato (Kyriacou et
al., 2009), Tomato (Javanmardi and Kubota, 2006), Mango (Abbasi et al., 2011),
Citrus (Mahajan, 2005) and Cherries (Martinez-Romero, et al. (2008).
4.4.2 Effect on Total Soluble Solids
Total soluble solid (TSS) in potato exhibited general increase during the
storage period with highly prominent elevation observed in T1. Treatment means
showed significant difference between them with maximum TSS estimated in T1
followed by T2 and T3. Storage interval means showed significant difference with
highest TSS retention recorded at the end of storage period with non significant
difference recorded between 70th, 98th and 112th days. The interaction between
treatments and storage intervals was highly significant with maximum TSS
estimated in T1 during most of the storage period (Fig. 36).
Storage at 5oC retained maximum TSS retention during most of the storage
period. TSS remained highest (6.90 oBrix) till 42nd day storage followed by steady
decline afterward. TSS accumulation remained steady at 25oC with final decline
(6.42 oBrix) observed on 84rth day storage. Storage at 15oC showed continuous
accumulation of TSS through out the storage period with maximum contents (6.55
oBrix) estimated on 126th day storage. Nevertheless TSS contents remained
considerably high in T1 than all other treatments with maximum percentage
increase recorded on 28th day (16.9%) followed by T3 on 70th day (13.42%) and T2
on 126th day (12.36%) storage.
171
5.5
5.9
6.3
6.7
7.1
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Tot
al s
olub
le s
olid
s (o
Bri
x)
5°C
15°C
25°C
Fig. 36 Total soluble solids in potato under comparative temperature storage showing maximum increase at 5oC (LSD (0.05) for treatment = 0.00517 LSD (0.05) for days interval = 0.00943 LSD (0.05) for interaction = 0.01633)
Vertical bars show ±SE of means.
172
TSS accumulation in potato under storage is associated with the hydrolytic
conversion of starch into soluble sugars (Kittur et al., 2001). The phenomenon is
highly desirable in most of the climacteric fruits and considered as ripening index.
Contrary to this the same is not required in potato due to poor processing
performance in frying. Interestingly potato crop exhibit increased total soluble
solids accumulation at diverse temperature regimes due to starch degradation
because of high respiration rate as well as cold sweetening below some critical
temperature. Thus the optimum storage temperature for particular potato variety is
very important for prolong storage. In the present study different temperature
levels showed variable response regarding their total soluble solids accumulation.
The significant TSS increase in T1 (5oC) might be due to rapid conversion of starch
into soluble sugars (Endo et al., 2006) primarily the sucrose which afterward
hydrolyzed into glucose and fructose due to activities of enzyme invertase. Steady
decline afterward might be due to the substrate oxidation during tuber respiration,
the similar findings have also been reported by Sonnewald, (2001). Storage under
other two temperature regimes showed steady increase in TSS due to slower starch
hydrolysis; however final decline observed in T3 might be due to increased
sprouting lead to oxidation of soluble sugars as respiratory substrate (Sowokinose,
1990).
4.4.3 Effect on Glucose
Glucose contents showed variable trend under different temperature storage
with prominent initial increase followed by steady decline in T1, steady increase in
T2 and steady increase with final decline in T3 during storage. Treatment means
revealed maximum glucose retention in T1 followed by T2 and T3. Storage interval
means exhibited significant difference between them with statistically similar
glucose contents found on 98th and 126th days (α-0.05). Interaction between storage
173
intervals and treatments was highly significant and showed maximum glucose
retention in T1 during most of the storage period (Fig. 37).
Storage of potato under 5oC temperature showed highly significant increase
in glucose contents as compare to other temperature regimes. This rise was
paramount and remained at highest value (842.11 mg/100g) by 1st month storage
followed by steady decline however remained more than 2-folds than other two
treatments during rest of the storage period. Steady increase in glucose contents
witnessed both under 15oC and 25oC temperatures storage and evolved within
close range but the rate of increase was found swifter in later than former. At 15oC
the maximum glucose contents (325.63 mg/100g) were estimated on 126th day
storage which was close to that identified in 25oC on 84rth day storage.
Potato storage under low temperature is carried out in order to prevent
potato sprouting through imposed dormancy (Wiltshire and Cobb, 1996). The
storage temperature is however associated with reducing sugar accumulation
predominantly present in the form of glucose and fructose, negatively correlated to
the fry color (Hermen et al., 1996) and also reported to be major precursor in toxic
acrylamide formation during processing (Amrein at al., 2004). Knowles et al.
(2009) studied the reducing sugar contents in different potato cultivars under low
temperature and found maximum during 1st month followed by gradual decline
showing partial acclimation. Rapid increase in reducing sugars under low
temperature storage was also reported by other researchers like Blenkinsop et al.
(2002), Chuda et al., (2003), Nourian et al. (2003) and Tamaki et al. (2003). Our
results regarding glucose contents showed that the influence of storage time was
less pronounced than the effect of storage temperature. Significant increase in
glucose contents at 5oC temperature confirmed the previously reported findings.
Steady increase in the glucose contents at temperature regimes i.e. 15oC and 25oC
174
0
150
300
450
600
750
900
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Glu
cose
(m
g/10
0g)
5°C
15°C
25°C
Fig. 37 Glucose in potato under comparative temperature storage showing maximum contents at 5oC (LSD (0.05) for treatment = 1.158 LSD (0.05) for days interval = 2.114 LSD (0.05) for interaction = 3.662)
Vertical bars show ±SE of means.
175
might be attributed to the effect of storage time being less significant as compare to
storage temperature. The presence of moderate glucose contents at intermediate
temperature (15oC, 25oC) confirmed the findings reported by other researchers like
Kyriacou et al. (2009), Edwards et al. (2002) and Nourian et al. (2003) who
presented low sugar contents in potato above 10oC storage. Our results showed low
glucose accumulation at 15oC and 25oC however the postharvest storage life was
significantly higher in former (126 days) than later (84 days) temperature storage.
The ultimate decline in glucose contents at 25oC might be due to its utilization as
respiratory substrate during high respiration rate due to sprouting and tuber
senescence (Kyriacou et al., 2008).
4.4.4 Effect on Total Sugars
Total sugars accumulation in response to different storage temperature was
consistent with that found for glucose contents. Generally total sugars increased in
all treatments followed by steady decline with highly significant rise estimated in
T1. Treatment means established significant difference between stored potato with
maximum and minimum sugar contents identified in T1 and T3 respectively.
Storage interval means demonstrated significant difference between them with
maximum sugar retention after three month storage. The interaction between
treatment means and storage intervals was found significant with maximum values
estimated in T1 during most of the storage period (Fig. 38).
Amongst all temperature levels maximum sugar contents were estimated in
5oC with dominant increase (< 3%) during 1st month storage and retained elevated
sugar contents in tubers till 56th day storage there after followed by steady decline
176
500
1000
1500
2000
2500
3000
3500
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Tot
al s
ugar
s (m
g/10
0g)
5°C
15°C
25°C
Fig. 38 Total sugar in potato under comparative temperature storage showing maximum contents at 5oC (LSD (0.05) for treatment = 3.762 LSD (0.05) for days interval = 6.86 LSD (0.05) for interaction = 11.90)
Vertical bars show ±SE of means.
177
during rest of the storage period. Sugar contents increased steadily under other
two temperature regimes with their maximum contents identified in T2 and T3 at
126th and 70th day respectively.Total sugar contents produced in potato primarily in
the form of sucrose, glucose and fructose due to starch degradation (Hajirezaei et
al., 2003). These sugar contents are metabolized during tuber respiration along
with their contribution in maillard reaction for non enzymatic browning during
processing. Although sucrose does not directly participate in maillard reaction but
contributes to chip color development due to its hydrolysis during frying
(Leszkwiat et al., 1990). Endo et al. (2006) compared the sugar accumulation in
some potato varieties under different temperature regimes (2oC, 6oC, 8oC, 10oC,
and 18oC) and reported maximum sugar contents below 8oC temperature. Similar
observations were recorded by Kyriacou et al. (2009), Kazami et al. (2000) and
Herman et al. (1996) who estimated inverse relationship between total sugar
contents and temperature in potato tubers under storage. In the present
investigation maximum sugar contents estimated at 5oC temperature confirmed the
finding reported by above researchers. At low temperature storage decrease in total
sugars was comparatively higher than glucose contents which might be attributed
to synchronize glucose addition due to sucrose cleavage mediated through vacuolar
invertase activity which also confirmed the findings by Junker et al. (2006).
4.4.5 Effect on Starch
Changes in starch contents under different temperature storage revealed
general decrease with the progress in storage period. Data related to treatment
means showed significant different between them with maximum and minimum
178
starch accumulation estimated in T2 and T3 respectively. Storage interval means
articulated significant difference between them with highest and lowest starch
contents estimated on 1st and 112th days respectively. Interaction between storage
interval and treatment means was highly significant with maximum starch contents
estimated in all treatments at the start of storage while lowest starch contents were
recorded in T1 at the end of storage (Fig. 39).
In general starch contents declined under all temperatures storage however
express percentage decline was recorded at 5oC and remained significantly lower
till the end of storage period (32.0%). Storage at 15oC retained appreciable starch
contents till 84rth day storage and reduction estimated was only 7.1% as compare to
29.5% and 21.5% decrease recorded in T1 and T3 respectively. Over all percentage
declines recorded at 15oC (16.1%) and 25oC (21.5%) till 126th and 84rth day storage
respectively. Contrary to other treatments, storage at 25oC presented minor initial
increase in starch contents there after followed by gradual decline. Storage at
ambient temperature (25oC) retained higher starch contents than 5oC and lower
than 15oC but the commercial storage life remained only up to 12 weeks as
compare to 18 weeks storage found at other two temperatures.
Starch is the predominant carbohydrate present in potato contributing 70-
80% of total dry matter contents and proportional to its specific gravity value
(Kazami et al., 2000). Starch contents have been observed to change during post
harvest storage and in turn affect the processing attributes of potato (Herman et al.,
1996). Starch and sugars are the principal chemical components in potato tubers
influenced by low temperature storage mediated through specific enzymes.
179
13
14
15
16
17
18
19
20
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Sta
rch (
%)
5°C
15°C
25°C
Fig. 39 Starch in potato under comparative temperature storage maintaining maximum contents at 15oC (LSD (0.05) for treatment = 0.0400 LSD (0.05) for days interval = 0.0730 LSD (0.05) for interaction = 0.1265)
Vertical bars show ±SE of means.
180
Nourian et al., (2003) studied the quality changes in potato at different
storage temperatures and found that starch contents decreased with the decrease in
storage temperature and increase in storage time. Similar observations proposed by
Rivero et al. (2003) who reported progressive decrease in starch and concurrent
increase in sugar contents with the increase in storage period. Low temperature
storage cause significant degradation of starch polymers into soluble sucrose due to
inactivation of glycolytic enzymes like Phosphofructokinase and fructose -6-
phosphate. Sucrose hydrolysis is mediated through enzyme invertase ultimately
results in the increase in reducing sugars like glucose and fructose (Sonnewald,
2001). The energy requirement of dormant potato tuber during post harvest storage
largely dependent on it starch contents.
Our results presented significant decline in starch contents both under low
temperature storage (5oC) and extension in storage period (126 days). However the
prominent decline under low temperature storage showed that the reduction in
starch content is largely a function of storage temperature than the storage time.
Significant decrease in starch contents at 25oC after two month storage till the end
(84 days) might be due to the sufficient energy required by the growing sprouts as
also been observed by Farre et al. (2001). Storage of potato tubers at intermediate
storage temperature (15oC) retained appreciable starch contents and extended the
storage life up to 126 days however associated with increase weight loss as
compare to low temperature storage (5oC). The results framed in the present study
confirmed the findings of previous researchers like Karim et al. (2008), Kumar et
al. (2004), Nourian et al. (2003) and Neilson et al. (1997).
181
4.4.6 Effect on Ascorbic acid
General trend was decrease in ascorbic acid (AA) contents in all treatments
however the retention of ascorbic acid was inversely proportional to the storage
temperature. Treatment means showed significant difference between them with
maximum AA contents in T1 followed by T2 and T3. Storage interval means
showed significant difference between them with minimum AA contents estimated
at the end of storage. Significant interaction between treatments and storage
intervals was observed with maximum AA estimated at start of storage while
minimum contents estimated in T2 and T3 at the end of their respective storage
period (Fig. 40).
Amongst different temperature studied storage of potato tubers at 5oC
presented lowest reduction in AA till 126 days storage. Percentage reduction in
ascorbic acid contents was 30.2%, 42.2% and 42% at 5oC, 15oC and 25oC
respectively till the end of their respective storage periods. AA contents estimated
at 5oC at the end of storage i.e. 126th day (17.45 mg/100g) was higher than that
quantified on 56th day (16.09 mg/100g) storage at 25oC temperature. Moderate
reduction in AA contents has been observed at 15oC with lowest value estimated
on 126th day storage which was similar to that recorded at 25oC on 84rth day
storage.
Ascorbic acid is one of the most important quality parameter in fruits and
vegetables and is attributed to significant functional importance in human
metabolism. Retention of AA contents in horticultural crops during post harvest
storage largely influenced by different factors like genotype, agronomic practices,
growing conditions, maturity, harvesting techniques and post harvest management
(Lee and Kader, 2000). The loss of ascorbic acid is however primarily associated
182
14
16
18
20
22
24
26
1 14 28 42 56 70 84 98 112 126
Storage Intervals (Days)
Asc
orbic
aci
d (m
g/10
0g)
5°C
15°C
25°C
Fig. 40 Ascorbic acid in potato under comparative temperature storage maintaining maximum retention at 5oC (LSD (0.05) for treatment = 0.08001 LSD (0.05) for days interval = 0.1461 LSD (0.05) for interaction = 0.2530)
Vertical bars show ±SE of means.
183
with inappropriate post harvest management of horticultural commodities.
Ascorbic acid is readily oxidized into dehydro-ascorbic acid in the presence of
molecular oxygen mediated through enzyme ascorbate oxidase (Saari et al., 1995).
Amongst different post harvest management techniques temperature management
is one of the key factor in AA retention under storage. The considerable retention
of this valuable antioxidant can be secured by apt selection of storage temperatures
and storage times. Nourian et al. (2003) studied the changes in ascorbic acid
contents under different temperature regimes and stated that the ascorbic acid
contents decreased with the increase in storage temperature and storage duration.
Similar results were reported by Blenkinsop et al. (2002) regarding decline in
ascorbic acid with the progression in storage time. The present investigation
revealed that the retention of AA contents in potato during their post harvest
storage is equally associated with their storage temperature and storage time. The
eventual decline in ascorbic acid at 5oC might be due to their degeneration under
prolonged storage as also reported by Davies et al. (2002). Lowest retention of AA
contents at 25oC as compare to other two temperature regimes (5oC, 15oC) and
significant decline in AA contents with the progression in storage time confirmed
the findings of the researchers reported above and also found in line with the
findings of other scientists like Tamaki et al. (2003), Rivero et al. (2003) and
Vorne et al. (2002).
4.4.7 Effect on Chlorophyll
In response to different temperature storage chlorophyll contents continue
to increase significantly with the progression in storage period. Treatments means
demonstrated maximum chlorophyll accumulation in T3 followed by T2 and T1.
Storage interval means showed significant difference in their chlorophyll contents
184
with non significant difference recorded between 1st and 14th days. The interaction
between treatments and storage intervals was found highly significant with
minimum contents estimated till second week storage in all treatments and
maximum recorded in T3 at the end of storage period (Fig. 41).
Chlorophyll contents continued to increase with the increase in storage
period however the increase was prominent at 25oC than other two temperature
regimes. The percentage increase in chlorophyll content at 25oC was around 3-
folds (1.83 mg/100g) till 84rth day afterward expired due to excessive weight loss
and sprouting. Storage of tubers at 5oC and 15oC temperatures showed minor
increase in Chlorophyll contents till 42nd day afterward substantial increase (1.70
mg/100g) witnessed at 15oC till 126th day storage. Lowest overall chlorophyll
contents were estimated in storage at 5oC with percentage increase remained less
than 2-folds (1.15 mg/100g) till the end of 126th day storage.
Increase in chlorophyll contents reported to alter the brightness in potato
tubers and the phenomenon is primarily associated with exposure to different
illuminations and temperature (Grunenfelder et al., 2006). Edward and Cobb,
(1997) studied the effect of different temperature levels (5oC, 10oC, 20oC, 25oC) on
chlorophyll accumulation in potato and observed maximum and minimum
accretion at 25oC and 5oC respectively. Increase in chlorophyll contents also
noticed under different temperature regimes in the present study and presented
considerable alteration in tuber color. Our results showed considerable increase in
chlorophyll contents with increase in storage temperature and storage duration.
Magnitude of chlorophyll accumulation increased with the
185
0.5
0.9
1.3
1.7
2.1
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Chl
orop
hyll (m
g/10
0g d
.w)
5°C
15°C
25°C
Fig. 41 Chlorophyll in potato under comparative temperature storage maintaining maximum contents at 25oC (LSD (0.05) for treatment = 0.02829 LSD (0.05) for days interval = 0.05165 LSD (0.05) for interaction = 0.08946)
Vertical bars show ±SE of means.
186
increase in storage temperature. The chlorophyll contents estimated at 25oC on 56th
day was higher than that identified at 5oC on 126th day storage. Over all results
showed that both storage temperature and storage durations were equally
associated with the increase in chlorophyll contents. These results are also found in
close agreement with the findings of Nourian et al. (2003).
4.4.8 Effect on Total Glycoalkaloids
Total Glycoalkaloids (TGA) accrual in terms of solanine equivalent showed
an increasing trend with the progression in storage period under all temperature
storages (Fig. 42). Treatment means showed significant difference between them
with maximum TGA contents estimated in T3 and minimum in T1. Most of the
storage interval means were found significantly different with non significant
difference identified in 56th and 112th days, 70th and 126th days. The interaction
between storage intervals and treatments was found less significant till 28th day
afterward exhibited maximum TGA accumulation in T3 at the end of storage
period (Fig. 42).
Storage of potato tubers under all temperature regimes showed increase in
TGA contents with the increase in storage time. Similar TGA contents had been
observed under all temperatures till 1st month storage there after more than 12-
folds increase estimated at 25oC till the end of storage. Moderate TGA contents
had been recorded at 15oC with around 7-folds increase till 126th day storage. In
comparison TGA contents quantified at 15oC on 126th day was less than that
estimated at 25oC on 84rth day storage. Storage at 5oC accumulated lowest TGA
contents till 126th day storage and remained around 5-folds increase till the end.
187
0
15
30
45
60
75
90
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
TG
A (m
g/10
0g d
.w)
5°C
15°C
25°C
Fig. 42 Total Glycoalkaloids in potato under comparative temperature storage showing lowest contents at 5oC (LSD (0.05) for treatments = 0.810 LSD (0.05) for days interval = 1.479 LSD (0.05) for interaction = 2.561)
Vertical bars show ±SE of means.
188
Nevertheless except in T3 at the end of storage the TGA increase remained under
safe human intake limit i.e. 20mg/100g f.w as suggested by Mensinga et al.,
(2005).
Sengul et al. (2004) concluded that mechanical damage, light and high
temperature is major environmental stress factors prompt TGA synthesis in potato
tubers during their post harvest storage. In the present study maximum TGA
accumulation at 25oC as compare to other storage temperatures confirmed the
above reported findings. Contradictory observations were proposed by Rita et al.
(2007) who found higher TGA accumulation in potato tubers at refrigerated
temperature than those placed under room temperature however he related the
varietal specific biosynthesis of TGA which might not be the case as in the present
study. Significant increase in TGA contents in response to elevated temperature
was reported by other researchers like Nema et al. (2008), Sengul et al. (2004) and
Rosenfeld et al. (1995)
4.4.9 Effect on Total Phenolic Contents
Storage of potato tubers under all temperature regimes showed general
parabolic trend with initial unparallel increase in Total Phenolic Contents
(TPC) followed by gradual inconsistent decline till the end. Treatment means
showed significant difference between them with maximum TPC estimated in
T1 and minimum in T3. Storage interval means revealed significant difference
between them with lowest TPC estimated at the start and end of the storage.
Significant interaction was observed between treatments and storage intervals
with maximum TPC contents estimated in T1 and T2 on 70th and 56th days
respectively (Fig. 43).
189
75
100
125
150
175
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
TP
C (
mg/
100g
d.w
)
5°C
15°C
25°C
Fig. 43 Total phenolic contents in potato under comparative temperature storage showing maximum retention at 5oC
(LSD (0.05) for treatment = 1.253 LSD (0.05) for days interval = 2.030 LSD (0.05) for interaction = 3.751)
Vertical bars show ±SE of means.
190
TPC increased in all treatments with the increase in storage duration
however 5oC retained appreciable contents as compare to other temperature
storages. Storage of potato tubers at 25oC showed initial increase in TPC till
1st month storage subsequently followed by extensive decline (80.52
mgGAE/100g) till 84rth day and not determined afterward due to loss of their
commercial significance. TPC increased continuously at 15oC till 70th day
thereafter presented considerable decline (121.70 mgGAE/100g) by the end
of storage period. Increase in TPC at 5oC also exhibited gradual increase
with no sign of cessation till the end of storage period (159.50
mgGAE/100g).
Total phenolic contents are the secondary metabolites present in
potato known to carry anti oxidant, anti cholesterol and anti malignant
properties (Andre et al., 2009). Potato are considered as one of the best
source of these polyphenolic compounds with contents varying between
170mg/Kg to 19mg/kg in peeled and cooked potato respectively (Mattila and
Hellstrom, 2007). TPC in potato are reported to influenced by different
intrinsic factors like color, variety (Lachman et al., 2008) as well as extrinsic
factor like growing locality, fertilization, post harvest storage conditions
(Hamouz et al., 2006). TPC accumulation in the potato and other plants is
attributed to their defence mechanism against different mechanical stress;
bruising, mechanical injuries conferred by unfavorable growing conditions,
in appropriate post harvest handlings, insects/pest infestations etc (Friedman,
1997). Temperature management during post harvest storage of potato is
widely approved technique to prolong the storage life by preventing water
loss and sprouting. Barberan and Espin, (2001) studied phenolic compounds
191
as quality determinant in different fruits and vegetable and reported their
appreciable retention at low temperature during post harvest storage. The
accumulation of phenolic contents in sweet potato in response to low
temperature storage has also been observed by Padda and Picha (2008). Vitti
et al. (2011) also observed increased phenolic contents in minimally
processed potato under 5oC and 15oC temperature storage. Significant
decline in TPC at 25oC after 2 month storage might be due to the tuber
closer to sprouting (Saltveit, 2000) consequently triggered rapid polyphenol
oxidase activities which lead to the decline in total phenolic contents.
Storage at intermediate (15oC) and low temperature (5oC) storages after an
initial increase (Madiwale et al., 2011) retained appreciable TPC contents
till the end which might be associated with their low PPO activities. The
results reported in the present study are also in line with the findings of other
researchers like Lachman et al. (2008) and Gonzalez et al. (2004).
4.4.10 Effect on Radical Scavenging Activity
In general influence of different temperatures on radical scavenging
activity (RSA) (anti oxidant activity determined in terms of % inhibition of
DPPH) showed initial increase followed by gradual decrease with the
progression in storage period. The ultimate decline in RSA was lowest in T1
as compare to other two temperature storages. Treatment means
demonstrated maximum activity in T1 followed by T2 and T3. Storage
interval means illustrated maximum activities after 1st month storage while
minimum RSA estimated at the start and end of storage period. Interaction
between treatment and storage interval during the trial was found
192
20
25
30
35
40
45
50
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
RSA
(%
)
5°C
15°C
25°C
Fig. 44 Radical scavenging activity in potato under comparative temperature storage showing highest activity at 5oC (LSD (0.05) for treatment = 0.362 LSD (0.05) for days interval = 0.642 LSD (0.05) for interaction = 1.113)
Vertical bars show ±SE of means.
193
highly significant with highest activities recorded in T1 and T2 on 70th and
56th days respectively (Fig. 44).
Significant increase in Radical scavenging activity witnessed in all
treatments till 1st month afterward declined at 25oC while continued to
increase at 5oC and 15oC till 70th day storage. Storage at 25oC showed
highest decline (23.00%) till 84rth day thereafter not estimated due to loss of
commercial viability in potato tubers. Closely similar RSA values were
estimated at 5oC and 15oC on 70th day however the later showed
considerable decline (28.23%) till the end of storage period. Storage at 5oC
showed gradual increase in RSA till 70th day however unlike other
treatments retained appreciable activity on 126th day (41.50%).
Oxidative stress conferred by free radicals considered as major factor
in various degenerative disorders and are capable of damaging essential
biomolecules (Haila, 1999). Anti oxidants are the substances reported to
prevent these bio molecules either by delaying cellular oxidable substrates or
by quenching the free radicals produced in the biological system
(Hejtmankova et al., 2009). Potato considered as substantial source of these
antioxidant compounds mostly present as ascorbic acids, polyphenols and
anthocyanins depending upon the type and color of potato varieties
(Lachman et al., 2008). The increase in RSA during storage expressed
consistent pattern with the total phenolic contents with some deviations.
Madiwale et al. (2011) and Blessington et al. (2007) reported increase in
antioxidant activity during the storage period which also reported in the
present study. Appropriate temperature management in potato storage
194
reported to enhance anti oxidant activity with stumpy post harvest losses.
Lewis et al. (1998) reported increase in phenolic and anthocyanin contents
consequently high anti oxidant activity in colored potato varieties under low
temperature storage. Similar results were reported by Christie et al. (1994)
who found increased phenol biosynthesis under low temperature storage
which confirmed the results reported in the present study. Significant decline
in RSA at 15oC and 25oC on 126th and 84rth day storage respectively might
be due to the loss of phenolic and ascorbic acid contents (reported in the
present study). Moderate decline in RSA activity was also observed at 5oC at
the end of storage which might only be due to the degeneration of ascorbic
acids under prolonged cold storage as also reported by Davies et al. (2002).
4.4.11 Effect on Polyphenol Oxidase Activity
In general polyphenol oxidase (PPO) activity in potato tuber was found
proportional to their storage temperature. Treatment means showed significant
difference in their PPO activity with maximum estimated in T3 and minimum in
T1. Storage interval means illustrated maximum PPO activity on 84rth while
minimum at 14th days of storage. The interaction between treatments and storage
intervals was found significant with maximum activity recorded in T3 at the end
of storage period (Fig. 45).
Significant decrease in PPO activity observed at 5oC temperature which
remained below their initial value till the end of storage period. The highest
percentage decline (41.6%) was estimated on 70th day after ward minor increase
in PPO activity recorded till 126th day.
195
15
30
45
60
75
90
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
PPO
(U
/g d
.w)
5°C
15°C
25°C
Fig. 45 Polyphenol oxidase in potato under comparative temperature storage showing lowest enzymatic activity at 5oC (LSD (0.05) for treatment = 0.351 LSD (0.05) for days interval = 0.785 LSD (0.05) for interaction = 1.115)
Vertical bars show ±SE of means.
196
PPO activity showed overall steady and comparatively swift increases in potato
stored at 15oC and 25oC respectively. Storage at 15oC showed minor decline
(2.5%) till 84rth day after ward illustrated percentage increase of 21.5% up to
126th day. Highly significant PPO activity estimated in potato stored at 25oC
during storage with maximum activity recorded was around 2.5 folds than the
initial value on 84rth day storage. Rapid increase in PPO activity was observed
after 1st month storage which persisted till the end.
Nourian et al., (2003) studied changes in quality attributes of potato
tubers stored under five different temperature regimes i.e 4oC, 8oC, 12oC, 16oC
and 20oC. He concluded that PPO activity in potato tuber is directly proportional
to their storage temperature. Amongst different temperatures studied he found
decrease and increase in PPO activity at 4oC and 20oC temperature respectively.
Similar results were also reported by Junior et al. (2002) who observed high PPO
activity in lettuce at 2oC than those placed at 10oC storage. Our results concluded
that amongst different temperature studied storage at 5oC efficiently retained low
PPO activity in turn improved storage stability of potato as compare to those
placed at intermediate (15oC) and ambient temperature (25oC) which confirmed
the above reported findings. Decrease in PPO activity at low temperature storage
in different potato cultivars has also been observed by other researchers like at
Moretti et al. (2002), Nunes et al. (2001), and Zorzella et al. (2003).
4.4.12 Effect on Peroxidase Activity
General trend regarding POD activity showed initial decrease followed by
eventual increase in T1 and T2 while continuous increase observed in T3 during
197
storage. Treatment means showed significant difference with maximum POD
activity recorded in T3 and minimum in T1. Storage interval means illustrated
steady increase in POD till fourth week followed by maximum activity estimated
on 84rth day. The interaction between treatments and storage interval was
significant with highest activity identified in T3 after 1st month storage (Fig. 46).
Storage of potato tubers at 5oC and 15oC revealed an initial increase
followed by final decrease at the end of 126th day. The decline in POD activity
was more pronounced (35.4%) at 5oC till 70th day afterward increased close to the
activity level estimated before the start of experiment. Storage of tubers at 15oC
also exhibited slight decrease in activity i.e. 9.6 U/100 g up to 56th day storage
there after increased up to 15.25 U/100 g on 126th day storage. Potato tubers
stored at 25oC attained significant increase in their POD activity through out the
storage period. The prominent increase in POD activity started after 1st month
storage and achieved more than 3-folds higher than the initial value on 84rth day.
POD and PPO are considered as the major enzymes in horticultural
commodities responsible for the quality loss due to phenolic dilapidation (Tomas-
Barberan and Espin, 2001) moreover in browning perspective synergistic effect
between these two enzymes have also been reported (Subramanian et al., 1999).
Aydin and Kadioglu, (2001) reported increased POD activity in fruits and
vegetables under stress conditions and with the progression in their physiological
stages i.e. senescence. Our results showed significant increase in POD activity
after 1st month onward till the onset of sprouting at 25oC which confirmed the
above reported observations.
198
5
15
25
35
45
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
PO
D (U
/100
g d.w
)
5°C
15°C
25°C
Fig. 46 Per oxidase in potato under comparative temperature storage showing lowest enzymatic activity at 5oC (LSD (0.05) for treatment = 0.1953 LSD (0.05) for days interval = 0.3566 LSD (0.05) for interaction = 0.6202)
Vertical bars show ±SE of means.
199
Vitti et al. (2011) studied enzymatic activity in different potato varieties like
Agata, Asterix and Monalisa at 5oC and 15oC and reported low POD activity in
former than in later temperature storage in all the tested varieties. Similar
observations were recorded by Cantos et al. (2002) who reported decline in
enzyme activity at 5oC in spunta cultivar. The lowest estimated POD activity at
5oC followed by 15oC in the present study is in line with the findings of
researchers stated above.
4.4.13 Effect on Chip Moisture Content
In general chip moisture contents (CMC) increased in response to
different temperature however an eventual decline observed only in T1 at the end
of storage period. Treatment means illustrated maximum CMC in T1 and T3 with
non significant difference estimated between them. Storage interval means
exhibited maximum CMC during 84rth day followed by 70th days. Non significant
difference was observed between most of the storage intervals in their CMC. The
interaction between treatments and storage was significant with maximum CMC
estimated in T3 on 56th day till the end of storage period (Fig. 47). Statistical
analysis revealed non significant difference between potato tubers in their CMC
stored at 5oC and 25oC however difference between their ultimate storage
duration remained highly significant with 126th (D10) and 84rth (D7) day storage
respectively. CMC increased by around 1.6-folds at 5oC storage till 42nd day after
ward decreased progressively with over all 1.34-folds increase estimated at the
end of storage. Storage at 25oC showed moderate increase in their CMC till 42nd
day there after exhibited progressive 2.25-folds increase till the end of storage
period. Storage of the potato tubers at 15oC temperature maintained moderate
200
1
1.5
2
2.5
3
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Chip
moi
stur
e co
nte
nts
(%
)
5°C
15°C
25°C
Fig. 47 Chip moisture content in potato under comparative temperature storage showing highest content at 25oC
(LSD (0.05) for treatment = 0.03652 LSD (0.05) for days interval = 0.0666 LSD (0.05) for interaction = 0.1155)
Vertical bars show ±SE of means.
201
increase in their CMC during most of storage period however ended with around
1.4-folds increase and found statistically similar to 5oC on 126th day storage.
Frying cause the removal of significant amount of water through potato
chip surface (Hubbard and Farkas, 1999) thus precisely termed as dehydration
process. The process is associated with significant reduction of moisture contents
in the processed products (chips, French fries etc) along with corresponding oil
uptake. Potato with high specific gravity and appreciable starch contents were
reported to produce potato chips with low moisture contents (Pinthus et al., 1995).
Kyriacou et al. (2009) evaluated processing potential of different potato varieties
under three temperature regimes (4.5oC, 8.5oC and 11oC). He concluded that the
starch degradation and sugar accumulation was inversely proportional to their
storage temperatures.
High initial CMC in potato stored at 5oC might be due to starch degradation
with concurrent accumulation of reducing sugars as also reported by the
researchers above. Storage at 15oC maintained appreciable starch contents with
intact cellular configuration thus presented steady increase in CMC till the end of
storage. CMC remained highest in potato stored at 25oC which might be the
function of storage duration rather than storage temperature. The increased CMC at
the end of storage is associated with significant starch degradation in potato close
to sprouting as also stated by Bielmelt et al. (2000). The significant correlation
between Chip moisture contents and starch contents has also previously reported
by researchers like Aguilera et al. (2000) and Kita et al. (2004).
202
4.4.14 Effect on Chip Fat Absorption
Irrespective of different temperature storages chip fat absorption (CFA)
increased with the progression in storage period however the increase was highly
prominent in T1 and T3 during the start and end of storage respectively. Treatment
means established minimum CFA in T2 followed by T1 and T3. Storage interval
means showed minimum CFA in 1st day and maximum during 84rth and 70th days
which were found at par statistically. Interaction between storage intervals and
treatment means was significant with highest CFA recorded in T1 on 84rth day
(Fig. 48). Data pertaining to CFA was found in consistent with that observed in
CMC under different storage temperatures. Variable trend regarding CFA in
potato chips was observed under studied temperatures. At 25oC temperature CFA
remained slow till 42nd day storage trailed by progressive increase of around 1.5-
folds till 84rth day storage. In comparison the increase observed in last 28 days
was higher than that estimated during the initial 42 days storage. As discussed
before tubers stored at 25oC were discarded after ward due to loss of their
commercial significance. CFA remained steady during most of the time under
15oC storage with over all around 1.2 folds increase observed on 126th day
storage. Storage at 25oC tuber placed under 5oC temperature revealed initial
increase in their CFA till 42nd day followed by steady decline ti1l the end. In
addition the increase in CFA was lower and storage duration was found
significantly higher than the tuber stored at 25oC.
CFA is associated with the removal of moisture contents through cellular
matrix leaving behind capillary pores which were consequently filled by oil as
observed by Mellema, (2003). Some of the important factors reported to affect chip
fat absorption in potato chips during processing include tuber specific gravity
203
30
33
36
39
42
45
48
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Chip
fat
abso
rpti
on (
%)
5°C
15°C
25°C
Fig. 48 Chip fat absorption in potato under comparative temperature storage showing highest value at 25oC (LSD (0.05) for treatment = 0.4494 LSD (0.05) for days interval = 0.8204 LSD (0.05) for interaction = 1.421)
Vertical bars show ±SE of means.
204
(Mehta and Swinburn, 2001), modification in size and thickness (Gamble and
Rice, 1988), modification in frying techniques (Mehta and Swinburn, 2001).
Amongst potato with high specific gravity and intact starch contents are the most
crucial factor in ultimate chip fat absorption during processing. Nielsen et al.
(1997) observed enzyme mediated reduction in starch contents in different potato
varieties under low temperature storage which caused significant quality loss
during processing. Kita, (2002) observed inverse relationship between tuber starch
contents and chip fat absorption. Storage at 5oC and 25oC presented high CFA in
potato chips which might be associated with starch degradation due to the low
temperature sweetening (Karim et al., 2008) and sprouting (Bielmelt et al., 2000)
respectively. Low fat absorption in potato placed at 15oC as compare to other
storage temperatures might be due to the presence of high dry matter and intact
starch contents which verified the previously reported findings by Kita et al.
(2004), Tawfik et al. (2002) and Hagenimana et al. (1998).
4.4.15 Effect of Chip Color
Chip Color (CCL) estimated in terms of approximate L-value under
different temperature showed general decrease with the increase in storage time.
Treatments means showed lowest CCL value in T1 while highest CCL was
observed in T2. Storage interval means showed maximum and minimum CCL
values on 1st and 126th days respectively. The interaction between treatments and
storage intervals was significant with lowest CCL value estimated in T1 during the
1st half of storage duration (Fig. 49). Storage at 5oC presented maximum
percentage decrease (24.6%) on 28th day which continued at the same level as well
till56thdaystorage.
205
45
50
55
60
65
70
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Chip
col
or (L
-val
ue)
5°C
15°C
25°C
Fig. 49 Chip color in potato under comparative temperature storage showing highest value at 15oC (LSD (0.05) for treatment = 1.121 LSD (0.05) for days interval = 1.625 LSD (0.05) for interaction= 3.545)
Vertical bars show ±SE of means.
206
The CCL values subsequently followed gradual increase and ended with ultimate
20% decrease from the initial value. Storage at 25oC retained fine CCL values till
42nd day storage afterward exhibited 20% on 84rth day storage which was similar to
that estimated at 5oC on 126th day storage. Significant retention of CCL values
were estimated at 15oC during most of the storage period with lowest eventual
percentage decline (8.72%) reported on 126th day storage.
Chip Color (CCL) is the most important factor for consumer acceptance
and is primarily associated with the presence of their reducing sugar contents
(Tamaki et al., 2003). The increased reducing sugar contents in potato lead to the
non enzymatic browning during processing as a consequence of maillard reaction
hence reduce the product quality (Herman et al., 1996). Storage at 15oC and 25oC
temperature showed minor tendency of decline in CCL value over storage period
in contrast the decline was rapid at 5oC with in 1st month of storage. It was evident
from our results that reducing sugars sharply increased at 5oC with in 1st week and
corresponded with the significant decline in CCL values during the same period.
This inverse relationship between reducing sugars and CCL was also been cited by
different researchers like Kyriacou et al. (2009) and Tamaki et al. (2003). Storage
at 15oC presented remarkable CCL values (approximate L-values) during most of
storage period in potato chips and found superior to those placed under other
temperature regimes (5oC, 25oC) which might be due to their low corresponding
reducing sugar contents as also verified by researchers like Kaul et al. (2010) and
Biedermann-Brem et al. (2003). Appreciable CCL values were estimated at 25oC
temperature till 42nd day storage followed by considerable decline till the end of
storage. This significant decline might be associated with starch depletion along
207
with the possible participation of dehydro-ascorbic acid in chip browning during
processing as also been reported by Blenkinsop et al. (2002).
4.4.16 Effect on Chip Crispiness
Chip crispiness (CCR) scores showed an initial increase followed by steady
decrease in T2 and T3 in contrast significant initial decline was observed in T1
which remained consistent till the end of storage period. Treatment means showed
significant difference between their CCR scores with maximum estimated in T2
followed by T3. Storage interval means demonstrated maximum CCR scores
during the 1st half of storage and minimum at the end of storage period. The
interaction between treatment means and storage intervals was found significant
with lowest CCR scores estimated in T1 and T3 on 42nd and 84rth days respectively
(Fig. 50). In different temperatures studied considerable decline in CCR scores
was observed at 5oC till the end of storage period. The initial percentage decrease
in CCR scores was around 50% on 42nd day after ward showed minor scores
(2.33/5.00) elevation till the end of storage period. Potato stored at other two
temperature regimes showed initial increase in CCR scores followed by gradual
decline. Storage at 25oC retained appreciable CCR scores till 56th day storage later
declined to lowest level (1.93/5.00) estimated on 84rth day. Storage at 15oC
presented maximum CCR scores during most of the storage period and retained
significant scores till 98th day however associated with mild decline (2.93/5.00) at
the end.
Like color, crispiness is an important quality index of processed potato
which determines the consumer acceptability. Due to its significant correlation
with this high quality product the potato chips are widely known as “potato crisps”
208
1
2
3
4
5
1 14 28 42 56 70 84 98 112 126
Storage intervals (day)
Cri
spin
ess
(sco
res)
5°C
15°C
25°C
Fig. 50 Chip crispiness in potato under comparative temperature storage showing highest value at 15oC (LSD (0.05) for treatment = 0.1488 LSD (0.05) for days interval = 0.2850 LSD (0.05) for interaction = 0.4705)
Vertical bars show ±SE of means.
209
world over. Frying operation is associated with the initial decrease in chip texture
due to starch gelatinization (Anderson et al., 1994) which is followed by
progressive increase in textural attributes due to crust hardening (Pedreschi et al.,
2001) generating characteristic crispy texture. Crispiness in potato is closely
associated with the initial quality of raw material and frying medium. The presence
of high starch contents (Kita et al., 1998) and non starch polysaccharides (Kita,
2002) are considered as the key determinant of final CCR scores. In addition the
crispiness also reported to be improved by the presence of saturated fatty acids in
the frying medium (Kita et al., 2005). Since the frying medium remained constant
in the present study the retention of high quality raw material in potato stored at
15oC retained significant CCR scores during most of the storage period. Significant
decline in CCR at 5oC storage might be attributed to the starch degradation and
maillard browning before and after processing thus acceded the findings by
different researchers reported above.
4.4.17 Effect on Chip Flavor
Chip flavor (CFL) scores demonstrated an initial increase followed by
steady decline in T2 and T3 in contrast significant initial decrease was observed in
T1 which remained consistent till the end of storage period. Treatment means
showed maximum CFL scores in T2 followed by T3. Storage interval means
illustrated maximum CFL scores between 1st to 56th day and minimum on 126th
day. The interaction between treatments and storage intervals was found significant
with maximum scores estimated in T2 on 56th day and minimum in T1 and T3 on
70th and 84rth days respectively (Fig. 51). Storage at different temperatures during
the present study illustrated decline in flavor scores with the progress in time.
210
1
2
3
4
5
1 14 28 42 56 70 84 98 112 126
Storage Intervals (Days)
Chip
fla
vor
(sco
res)
5°C
15°C
25°C
Fig. 51 Chip flavor in potato under comparative temperature storage showing highest value at 15oC (LSD (0.05) for treatment = 0.1506 LSD (0.05) for days interval = 0.2750 LSD (0.05) for interaction = 0.4762)
Vertical bars show ±SE of means.
211
In general CFL scores showed similar trend as in other sensorial attributes studied.
Significant decline in CFL scores was observed at 5oC which remained almost
constant till the end of storage (2.40/5.00). Storage at 15oC and 25oC retained
improved flavor scores during most of their respective storage periods however,
the eventual decline remained high at 25oC (2.00/5.00) as compare to storage at
15oC (3.30/5.00). Over all storage at 15oC maintained appreciable CFL scores than
the other studied temperature regimes.
Flavor is the combination of taste and aroma attribute in food products.
Chip Flavor scores are affected by tuber composition, frying oil quality and frying
time and temperature (Martin and Ames, 2001). Prominent chip flavor evolution
has been attributed to the frying oil composition which acts as heat transfer
medium and flavor precursor during frying (Warner et al., 1997). Maillard
reaction between reducing sugars and amino acid contents reported to produce dark
colored flavoring compounds along with suspected toxic i.e. acrylamides. The
presence of these compounds confers dark chip color and bitter flavor in processed
potato products. Amongst different chemical constituents tuber reducing sugars
and amino acids are primarily responsible for this off flavor development in potato
chips. Appreciable CFL scores identified at 15oC during storage might be
attributed to their low reducing sugars as compare to tubers stored under other
temperature regimes. The low CFL scores at 5oC due to off flavor development
might be associated with acrylamide formation during processing. The significant
relationship between chips flavor development and reducing sugars contents was
also reported by different researchers like McCann et al. (2010) and Kaul et al.
(2010).
212
4.5 EFFECT OF DIFFERENT ANTI SPROUTING AGENTS ON THE
QUALITY ATTRIBUTES OF POTATO
Application of different anti sprouting agents was carried out as last
experiement of the 2nd phase of study. The response of Potato variety “Lady
Rosetta” to different anti sprouting agents like hot water treatment, spearmint oil,
clove oil and CIPC were studied. The quality attributes of potato tubers and
processing performance of potato chips were studied weekly during their post
harvest storage.
4.5.1 Effect on Weight loss (%)
Treatments with different sprout inhibitors and control showed increase in
weight loss (%) in potato during storage; however the rate of increase in weight
loss was higher in control as compare to other treatments. Treatment means and
storage interval means demonstrated significant difference amongst all the
treatments and storage intervals respectively. The interaction between treatment
means and storage intervals was found highly significant at the end of storage
where maximum weight loss percent was recorded in T1 followed by T2 (Fig. 52).
Highest weight loss (13.13%) was recorded in control whereas amongst
different anti sprouting agents CIPC application (T5) expressed lowest weight loss
(7.70%) followed by Clove Oil application (8.52%) till the end of storage period.
The application of hot water treatment (T2) and spearmint oil (T3) also retained the
tubers stability with moderate weight loss i.e. 9.25% and 10.70 % respectively as
compare to control. Amongst all treatments weight loss steadily increased due to
adequate suberization till 36 days storage (0.00% - 4.05%) which afterward
progressively increased up to 13.13 % in control as compare to 7.70%
213
0
2.5
5
7.5
10
12.5
15
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Wei
ght
loss
(%
)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 52 Weight loss in response to different sprout inhibitors showing minimum loss in CIPC during potato storage (LSD (0.05) for treatment = 0.058 LSD (0.05) for days interval = 0.082 LSD (0.05) for interaction = 0.184)
Vertical bars show ±SE of means.
214
increased up to 13.13 % in control as compare to 7.70% in CIPC treated potato by
the end of 80 days storage.
The weight loss due to respiration and evapo-transpiration triggers series of
complex metabolic activities thus considered as an important stability index for the
storage life assessment in horticultural products. The physiological phenomenon
hastens in potato as a result of sprouting under prolonged storage. The advent of
sprouts under storage obstructs the gases exchange through tuber surface which
eventually lead to the increased rate of respiration and weight loss. Pandey et al.
(2007) compared physiological weight loss in different potato varieties in response
to their sprouting behavior. He found highly significant correlation between weight
loss and sprouting behavior in selected varieties.
The present study also showed increased weight loss (%) with the onset of
sprouting in potato and found more pronounced in control. Use of different anti
sprouting agents in the present study effectively retained tuber dormancy at
varying level in potato during storage. Hot water treatment effectively retained
tuber stability till eight week storage however associated with increased weight
loss due to sprouting and tuber softening during last month of the storage. The
results partially confirmed the findings of Ranganna et al. (1998) who reported 12
weeks storage stability of potato under hot water treatment the difference in
storage stability period might be due to the tuber variety and difference in storage
temperature. The application of essential oils reported to be environment friendly
(Oosterhaven et al., 1995) and also served as protection line against insects and
pest intervention (Rajendran and Srirajini, 2007). Our results framed in the present
study showed that application of clove oil and spearmint oil effectively improved
215
the storage stability of potato with lower weight loss as compare to control. The
efficacy of clove oil application in terms of weight loss (%) was found superior to
spearmint oil and comparable to the commercial CIPC application during storage.
The response of essential oils specifically clove oil application in sprout prevention
was found highly significant which confirmed the findings reported by different
researchers like Vaughn and Spencer (1993), Kleinkopf et al. (2003), Frazier et al.
(2004), Teper-Bamnolker et al. (2010) and Chauhan et al. (2011). Minimum
weight loss (%) in CIPC application was observed in the present study however the
application of this commercial sprout inhibitor became the concern of environment
and food safety (Kleinkopf et al., 2003). Nevertheless in the present study
amongst all treatments the application of CIPC showed least weight loss (%) and
prolonged storage stability in potato during storage which coincided the previous
observations reported by Meredith, (1995), Blenkinsop et al. (2002) and Frazier et
al. (2004).
4.5.2 Effect on Total Soluble Solids (oBrix)
Total soluble solid (TSS) accumulation in potato in response to different
anti sprouting agents exhibited general increase during the storage period. The
increase in TSS was more pronounced in T1 as compare to all other treatments.
Treatment means specified lowest TSS retention in T5 and T4 which were found at
par statistically. All other treatments means showed significant difference between
them. Storage interval means in general showed non significant difference in TSS
till the mid storage which became significant during 2nd half of storage period and
found maximum at the end. In general non significant interaction between
216
treatment means and storage intervals means became significant after the mid
storage period (Fig. 53).
TSS accumulation due to different anti sprouting agents was steady during
the early weeks and progressively increased with the storage duration. Maximum
TSS accumulation was observed in Control (6.68 obrix) followed by hot water
treatment (6.40 obrix) at the end of storage. Spearmint, Clove, and CIPC retained
6.25 obrix, 6.19 obrix and 6.16 obrix TSS respectively by the same storage period
with non significant difference recorded between them.
Change in TSS is directly associated with the conversion of insoluble starch
polymers into soluble sugars (Kittur et al., 2001) and unlike other horticultural
commodities is highly redundant during potato post harvest storage. Possible
explanation for the disparity in TSS contents observed in different treatments
during the present study might be due to the starch degradation into soluble sugars
at varying levels. Sonnewald, (2001) reported that during sprouting potato tuber
turn into source organ required for the elongation of sprouts and is primarily
associated with the starch degradation into soluble sugars. The application of
different anti sprouting agents might have checked the physiological conversion of
starch into soluble sugar due to sprout inhibition. Elevated TSS contents recorded
in control and hot water treatment at the end of storage might be attributed to
increased moisture loss as compare to other treatments during storage. The
application of spearmint and clove oil presented reasonable TSS accumulation in
tubers as compare to control might be due to suppressed sprout growth. CIPC
application reported to inhibit potato sprouting by obstructing the mitotic cell
division, dislocates spindle formation (Kleinkopf et al., 2003), and supress the
217
5.4
5.7
6
6.3
6.6
6.9
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Tot
al s
olu
ble
sol
ids
(oB
rix)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 53 Total soluble solids in response to different sprout inhibitors showing maximum increase in control during potato storage
(LSD (0.05) for treatment = 0.02806 LSD (0.05) for days interval = 0.03968 LSD (0.05) for interaction = 0.08873)
Vertical bars show ±SE of means.
218
respiration rate in potato during storage (Blenkinsop et al., 2002). In the present
investigation CIPC application retained minimum TSS contents at the end of
storage which might be attributed to suppressed respiration rate in potato tubers
thus prevented starch hydrolysis during the potato storage.
4.5.3 Effect on Sprouting (%)
In response to different anti sprouting agents data related to sprouting (%)
showed onset of sprouting in T1 and T2 by the mid storage period. Treatment
means showed minimum sprouting (%) in T6 and T5 with non significant difference
observed between them. All other treatments showed significant difference in their
sprouting (%) during storage. The storage interval means showed non significant
difference till the mid storage period which later on expressed significant
difference till the end. Significant interaction between treatments and storage
intervals was observed only during the last month storage (Fig. 54).
Potato tubers maintained their natural dormancy period irrespective of the
treatments till 1st month storage. The visible sprouts started to appear in Control
(12.17%) and hot water treated tubers (2.13%) on 36th day storage however the
percentage increase in sprouting (%) in control remained soaring and found 2-folds
as compare to hot water treated potato by the end of storage. Sprouting (%) in
control at 54rth day storage was considerably higher than those estimated in hot
water treated potato at the end of storage. Visible sprouts started to appear in
spearmint, clove and CIPC treated potatoes by 54rth, 63rd and 63rd day storage
respectively.
219
0
20
40
60
80
100
120
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Spro
uting
(%)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 54 Sprouting in response to different sprout inhibitors showing maximum percentage in control during potato storage (LSD (0.05) for treatment = 1.353 LSD (0.05) for days interval = 1.913 LSD (0.05) for interaction = 4.278)
Vertical bars show ±SE of means.
220
Lowest sprouting (%) was estimated at the end of storage in CIPC exposure
(16.40%) followed by Clove oil application (20.57%) with non significant
difference observed between them.
Tuber dormancy during post harvest storage may precisely be termed as
endo dormancy defined as the physiological tuber stage at which sprouting failed
to occur even under favorable conditions. The appearance of visible sprouts
following the period of endo dormancy is one of the peculiar features of potato
post harvest storage (Sonnewald, 2001). The onset of sprouting causes significant
economic hammering due to considerable weight loss and tuber quality
consequently increases the chance of disease attack and poor post harvest storage
life. Significant difference was observed between control and different anti
sprouting agents employed in the present study. The application of different anti
sprouting agents effectively prolonged tuber dormancy as compare to control at
ambient temperature. The use of essential oils especially clove oil exhibited almost
parallel sprouting percentage with CIPC application at ambient temperature. Our
investigations confirmed the effectiveness of different anti sprouting agents like
hot water treatments, spearmint oil, clove oil and CIPC application as reported by
previous researchers like Ranganna et al. (1998), Kleinkopf et al. (2003) and
Frazier et al. (2004).
4.5.4 Effect on Specific Gravity
Specific gravity value in potato showed initial increase followed by a
gradual decline at the end of storage. The rate of decrease in specific gravity value
was higher in T1 as compared to other treatments. Treatment means revealed non
significant difference between T4 and T5, T2 and T3 in response to different anti
sprouting agents. Storage interval means remained statistically non significant
221
during most of storage except during 1st week and last month storage. In general
except in T1 and during the last week storage interaction between treatments and
storage intervals was also found non significant (Fig. 55). Gradual specific gravity
increase witnessed in Control, hot water treatment and all other treatments till 27th
day, 45th day and 54rth day respectively and declined afterward till the end of
storage. The decline in specific gravity was highest in control (1.091) and found
lowest in CIPC application (1.107). In general maximum specific gravity values
were identified during the mid storage period amongst all the treatments.
In general the application of different anti sprouting agents affected the
specific gravity values in potato during storage as compare to control however the
influence with in the treatments remained less significant. The similar results were
reported by Cunningham et al. (1971) who studied the effect of temperatures
(38oF, 45oF and 52oF) and sprout inhibitors (MH, CIPC) on the specific gravity of
Russet Burbank potatoes and reported the value is more dependent on storage
temperature than sprout inhibitors. Claassens and Vreugdenhil (2000) reported that
potato tuber with the onset of sprouting initiated rapid depletion of starch
reservoirs eventually lead to the over all decrease in specific gravity value.
Decline in specific gravity value amongst different treatments in general and in
control and hot water treated potatoes in particular closed to sprouting confirmed
the findings reported above
4.5.5 Effect on Glucose
Effect of different anti sprouting agents on glucose contents in potato tubers
showed steady increase during present study with considerable retention observed
in control at the end of storage. Treatment means showed significant difference
222
1.09
1.095
1.1
1.105
1.11
1.115
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Spec
ific
Gra
vity
Control
Hot water
Spearmint
Clove
CIPC
Fig. 55 Specific gravity in response to different sprout inhibitors showing lowest value in control during potato storage (LSD (0.05) for treatment = 0.001620 LSD (0.05) for days interval = 0.002291 LSD (0.05) for interaction= 0.005000)
Vertical bars show ±SE of means.
223
in recorded glucose contents with T1 retained maximum while T5 retained
minimum. Storage interval means also exhibited non significant difference with
maximum recorded in the last week while minimum during first week storage. The
interaction between storage intervals and treatments revealed significant difference
at the later stages of storage (Fig. 56).
Glucose contents continued to increase at steady pace during the 1st half of
storage and than progressively increased till the end of storage. Application of
different anti sprouting agents retained lower glucose contents (less than 100
mg/100g) than control (195.33 mg/100g) on 45th day storage however afterward
increased swiftly in control (313.0 mg/100g) and hot water treated potatoes
(207.73 mg/100g) till the end. Essential oils and CIPC applications also exhibited
increased glucose contents at the end of storage but remained below 200 mg/100g.
Non significant difference was recorded between them during most of the storage
period till pronounced increase (191.53 mg/100g) in glucose contents estimated in
spearmint treated potato at the end of storage. CIPC application maintained lowest
glucose contents (147.53 mg/100g) followed by clove oil applications (153.73
mg/100g) during the same storage period.
The prominent increase in glucose contents at the later stage of storage in
treatments like control and hot water treated potato might be due to the depletion
of carbohydrates reserves in tuber close to their sprouting (Sowokinose, 1990). The
presence of reducing sugar contents in processing potato is very critical and
negatively correlated with chip fry color (Blenkinsop et al., 2002). Potato
sprouting is primarily associated with carbohydrate mobilization i.e. conversion of
224
0
50
100
150
200
250
300
350
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Glu
cose
(m
g/10
0g)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 56 Glucose in response to different sprout inhibitors showing highest increase in control during potato storage (LSD (0.05) for treatment = 1.561 LSD (0.05) for days interval = 2.207 LSD (0.05) for interaction = 4.936)
Vertical bars show ±SE of means.
225
starch into soluble sugars required for the growth of sprouts. Burton et al. (1992)
reported elevated reducing sugar contents in potato close to sprouting as also
experienced in different treatments. To prevent potato from sprouting they are
either placed under suitable low temperature storage or exposed to different anti
sprouting agents. Different researchers like Liu et al. (1990) and Vanes and
Hartmans, (1987) reported elevated reducing sugar contents in tubers due to CIPC
application at the end of storage which was not according to our present
investigation. The possible reason might be due to comparatively less storage
duration and temperature difference established in the present study. The
application of different anti sprouting agents like Maleic hydrazide (Caldiz et al.,
2001), CIPC (Fauconnier et al., 2002), hot water treatment (Kyriacou et al., 2008)
reported to produce potato chips with better frying color due to decreased reducing
sugar contents which confirmed the results expressed in the present study.
4.5.6 Effect on Total Sugars
Effect of different anti sprouting agents on total sugar in potato tubers was
found almost similar to glucose accumulation pattern during storage. General trend
was an increase in total sugar contents with time and retained significant level in
control at the end of storage period. Treatment means revealed significant
difference between potato exposed to different anti sprouting agents and those
placed as control. Storage interval means showed significant difference between all
values with maximum sugar retention at the end of storage. The interaction
between treatment and storage intervals was found highly significant after 2 month
storage period (Fig. 57).
226
800
900
1000
1100
1200
1300
1400
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Tot
al s
uga
r (m
g/10
0g)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 57 Total sugar in response to different sprout inhibitors showing highest increase in control during potato storage
(LSD (0.05) for treatment = 8.44 LSD (0.05) for days interval = 11.94 LSD (0.05) for interaction = 26.70)
Vertical bars show ±SE of means.
227
Amongst different anti sprouting agents minimum increase in total sugar
contents was recorded in CIPC (0.84% to 0.99%) followed by Clove oil (1.033 %),
spearmint oil (1.039%) and Hot water (1.107%) applications. Potato placed under
control started to accumulate substantial total sugar contents by 36th day storage
and continued to attain maximum sugar contents (1.30%) till the end of storage.
Total sugar contents are present in potato primarily in the form of non-
reducing sucrose and reducing glucose and fructose (Blenkinsop et al., 2002). The
hydrolysis of sucrose mediated through enzyme invertase may leads to the
formation of glucose and fructose monomers thus also contributing to the poor
tuber quality during storage (Kumar et al., 2004). Different anti sprouting
applications was found efficient in maintaining induced dormancy period in potato
as compare to control. These applications either as sprout inhibitor (CIPC) or
sprout suppressant (clove oil, spearmint oil, hot water treatment) maintained low
sugar contents as compare to control. The maximum sugar retention was reported
at the end of storage period in control which might be attributed to its high
sprouting percentage (as reported in table 4) at the end of storage period these
finding accede the same as stated by (Kyriacou et al., 2008), Fauconnier et al.
(2002) and Sowokinos, (1990)
4.5.7 Effect on Starch
The variation in starch contents in potato tubers in response to different anti
sprouting agents revealed steady initial increase followed by progressive decline
during the storage period. Data pertaining to treatment means showed maximum
starch retention in T5 followed by T4 and T3 while minimum starch contents were
228
estimated in T1 followed by T2 during the storage period. Storage interval means
expressed significant difference between them with maximum and minimum starch
retention observed on 2nd and 12th week storage respectively. Interaction between
storage interval and treatment means was found highly significant after 7th week
storage (Fig. 58). Starch contents increased initially in freshly cured potato tubers
and generally found maximum between 2nd to 4rth week storage. Hot water treated
tubers and CIPC application retained appreciable starch contents as compare to
control. Application of different essential oils (spearmint, clove) as anti sprouting
agent also maintained palpable starch contents as compare to control by the end of
storage. The percentage decline in starch contents from 1st day value was found
minimum in CIPC (13.69%) followed by Clove Oil (14.46%) applications in
contrast to maximum percentage decline observed in control (23.58%). By the end
of storage appreciable starch contents was estimated in potato exposed to different
anti sprouting agents as compare to control.
Sugars produced during photosynthetic activities in the potato leaves are
translocated to the growing potato stem tubers and stored in the form of starch
(Fernie et al., 2002). The textural attributes in potato tubers like consistency,
mealiness, sloughing etc are largely associated to its starch properties which in turn
effected by different physiologically active processes like transpiration,
redistribution and respiration. The hydrolysis of starch molecules is mediated
through the activities of gluco-amylases breaking the α-1→6 links of amylopectin
generating linear molecules of amylase which subsequently hydrolysed by
invertase and amylases to produce sucrose and reducing sugars respectively
(Marchal, 1999).
229
14.5
15.5
16.5
17.5
18.5
19.5
20.5
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Sta
rch
(g/
100g
)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 58 Starch in response to different sprout inhibitors showing maximum contents in CIPC and clove during potato storage
(LSD (0.05) for treatment = 0.0930 LSD (0.05) for days interval = 0.1316 LSD (0.05) for interaction = 0.2943)
Vertical bars show ±SE of means.
230
The starch hydrolysishowever provides sufficient energy for the growth and
development of sprouts (Biemelt et al., 2000). In the present study use of different
anti sprouting agents maintained induced tuber dormancy and retained palpable
starch contents for more than two month as compare to control at ambient
temperature. The initial increase in starch contents was found less pronounced in
hot water treated potato and CIPC applications which might be due to the tuber
stress (Tsouvaltzis et al., 2011) and ceased mitotic activity (Meridith, 1995)
respectively. Nevertheless their application retained intact starch contents during
storage as compare to control. The application of these anti sprouting agents in the
present study for improved storage stability of potato tubers confirmed the results
reported by Ranganna et al. (1998) Frazier et al. (2004) and Kleinkopf et al.
(2003).
4.5.8 Effect on Total Glycoalkaloids
Total Glycoalkaloids (TGA) estimation in terms of solanine equivalent
showed steady initial increase till one month followed by progressive accumulation
by the end of storage period. The application of different anti sprouting agents on
potato tubers retained less TGA content than the control (Fig. 59). Significant
difference observed between different treatment means with maximum and
minimum contents found in T1 and T5 respectively. Storage interval means showed
significant difference in their TGA contents and found maximum at the end of
storage. The interaction between storage intervals and treatments was found
significant after 1st month storage (Fig. 59).
Increase in TGA contents remained non significant during the 1st month
storage irrespective of applied treatments. Lowest TGA content were estimated in
CIPC (47.7 mg/100g d.w) and clove oil (53.70 mg/100g d.w) application at the
end of storage which were found parallel to those identified in control on
231
5
25
45
65
85
105
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
TG
A (
mg/
100g
d.w
)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 59 Total glycoalkaloids in response to different sprout inhibitors showing lowest increase in CIPC and clove during potato storage (LSD (0.05) for treatment = 0.9058 LSD (0.05) for days interval = 1.2810 LSD (0.05) for interaction = 2.8650)
Vertical bars show ±SE of means.
232
45th day storage. Amongst different anti sprouting agents marked increase in
TGA contents (50.70 mg/100g d.w and 58.30 mg/100g d.w) started in hot water
treatment and spearmint oil on 63rd and 72nd days of storage respectively. The
progressive increase in TGA contents observed in control and hot water treated
potato after the mid storage period and exceeded the safe human intake limit i.e.
20mg/100g f.w (Mensinga et al., 2005) on 72nd (83.43 mg/100g d.w) and 81st
(79.47 mg/100g d.w) days respectively.
Smith et al. (1996) studied TGA contents in different part of potato plant
and reported maximum concentration in sprouts and flowers. Similar
observations have been reported by Kozukue et al. (2001) who determined high
TGA contents in potato is proportional to their sprouting potential during storage.
Nema et al. (2008) reported that sprouting is one of the principal factors
responsible for glycoalkaloids formation in potato during post harvest storage.
Application of different anti sprouting agents retained TGA contents with in the
food safety at ambient temperature except in hot water treated potato at the end of
storage. Our results revealed significant TGA contents in control and hot water
treated potato that might correspond to their high sprouting percentage observed
at the end of storage. Similar close relationships between TGA contents and
potato sprouting were also reported by other researchers like, Sengul et al.
(2004), Friedman et al. (2003) and Percivel et al. (1993).
233
4.5.9 Effect on Total Phenolic Contents
In general Total Phenolic Contents (TPC) estimated in terms of gallic
acid equivalent expressed initial increase followed by gradual decline till the
end of storage period. Significant retention of TPC however observed in
different treatments as compare to control. Treatment means showed
significant difference in their TPC in response to different anti sprouting
applications. T4 maintained maximum TPC followed by T5 while minimum
were observed in T1. Storage Interval means expressed significant
differences with maximum and minimum TPC determined after one month
and before the start of storage respectively. The interaction between
treatments and storage intervals showed maximum TPC contents in T3 and
T4 on 54rth day storage (Fig. 60).
TPC increased amongst all treatments till 36th day storage and
afterward started to decline in control till the end of storage. Significant
decline in TPC in response to different anti sprouting agents witnessed after
63rd day storage however the final retention amongst treatments remained
variable. CIPC (143.50 mg/100g) and clove oil (142.57mg/100g) application
retained appreciable TPC even after 80 days storage and found around
double than that estimated in control (70.17 mg/100g) during the same
period. Amongst different anti sprouting agents Clove and spearmint
applications retained maximum TPC accumulation through out the storage
period.
234
60
90
120
150
180
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
TP
C (
mgG
AE
/100
g d
.w
Control
Hot water
Spearmint
Clove
CIPC
Fig. 60 Total phenolic contents in response to different sprout inhibitors showing maximum retention in CIPC and clove during potato storage (LSD (0.05) for treatment = 1.731 LSD (0.05) for days interval = 2.448 LSD (0.05) for interaction = 5.474)
Vertical bars show ±SE of means.
235
Biosynthesis of TPC involves de amination of amino acid phenyl
alanine which acts as their precursor (Hamauzu, 2006). TPC bestow
significant functional attributes to fruits and vegetables groups owing to
their high anti oxidant activity (Kaur and Kapoor, 2002). Maximum retention
of TPC in potato tubers during storage is associated with low polyphenolase
activity which is responsible for potato browning (Anthon and Barrett, 2002).
Sufficient retention of TPC was observed in clove and spearmint oil
applications however the eventual decline in spearmint oil was more
prominent due to sprouting. In contrast to essential oils (Clove and
spearmint) increase in TPC during storage was found less prominent in CIPC
and hot water treatments which might be due to mitotic inhibition (Kleinkopf
et al., 2003) and degradation of heat sensitive phenolic substances (Kalt et
al., 2005) respectively conferred by applied anti sprouting agents. Our
results revealed considerable effect of anti sprouting agents on TPC
retention in stored potatoes as compare to control. The presence of sufficient
molecular oxygen and subsequent sprouting in control caused significant
decline in TPC as compare to other treatments.
4.5.10 Effect on Radical Scavenging Activity
Radical scavenging activity (RSA) estimated in terms of % inhibition
of DPPH showed minor initial increase followed by gradual decrease during
potato storage. The decrease in RSA was highly pronounced in control as
compare to other treatments. Treatment means showed significant difference
between them with T4 maintained maximum activity followed by T5 and T3.
T1 showed least RSA activity during storage period followed by T2. Storage
236
interval means showed maximum activity after one month storage which
afterward declined with time and found minimum at the end of storage.
Interaction between treatments and storage intervals was found significant
with maximum activity recorded in T4 on 45th day storage (Fig. 61).
In general steady initial increase was observed at the start of storage
in all treatments which became highest by the end of 1st month. Unlike
gradual decline observed afterward in control and hot water treated potatoes
the activity continued to increase in CIPC, clove oil and spearmint oil till
45th day storage. Amongst different anti sprouting agents CIPC (38.20%)
and clove oil (37.73%) applications retained substantial activity till the end
of storage. Application of spearmint and hot water treatment also presented
sufficient activity i.e. 24.67% and 24.57% respectively as compare to control
(19.50%) and found statistically similar at the end of storage.
Fruits and vegetables due to their high flavonoids, vitamins,
tocopherols and poly phenolic contents carry high radical scavenging
activity (Chu et al., 2000). In the present investigation general initial increase
in RSA activity during 1st month storage might be due to the increase in total
phenolic contents during the start of storage period (Padda and Picha, 2008).
The subsequent decrease in RSA activity in control followed by hot water
treatment and spearmint oil application might be due to the loss of ascorbic
acid and tissue senescence (Srilaoung and Tatsumi, 2003). The sprouting in
potato is associated with the remarkable increase in reactive oxygen species
like hydrogen per oxide (H2O2) (Bajji et al., 2007). The stability in RSA
activity was observed along the onset of sprouting in control might be due
237
10
20
30
40
50
60
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
RSA
(%
)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 61 Radical scavenging activity in response to different sprout inhibitors showing highest activity in CIPC and clove during potato storage (LSD (0.05) for treatment = 0.6474 LSD (0.05) for days interval = 0.9155 LSD (0.05) for interaction = 2.0470)
Vertical bars show ±SE of means.
238
to the pronounced activities conferred by anti oxidant enzymes like
peroxidases and catalases against these reactive oxygen species. Our results
revealed that application of different anti sprouting agents were found
effective in maintaining appreciable RSA activity in turn better storage
stability as compare to control.
4.5.11 Effect on Polyphenol Oxidase Activity
In response to different anti sprouting agents polyphenol oxidase (PPO)
activity in potato showed steady increase with the progression in the storage
period however the increase was found more momentous in control as compare to
other treatments. Treatment means demonstrated maximum activity in T1
followed by T3 while minimum were recorded in T2, T4 and T5 and were found
statistically similar. Storage interval means showed minimum PPO activity till 1st
week and than increased significantly till the end of storage. Interaction between
storage intervals and treatments was significant with maximum activity estimated
in T1 during last month storage (Fig. 62).
Except in hot water treated potato amongst all the treatments studied PPO
activity continued to increase steadily with no sign of termination till the end of
storage time. The increase in PPO activity was highly significant (76.88 U/g) in
control with more than 2-folds increase at the end of storage. Hot water treatment
presented significant reduction in their PPO activity and remained lower than
their 1st day value till 45th day storage followed by around 2-folds (60.89 U/g)
increase till the end of storage time. Enzyme activity observed in different anti
sprouting agents including the hot water treatments at the end of storage
239
15
30
45
60
75
90
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
PP
O (U
/g d
.w)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 62 Polyphenol oxidase in response to different sprout inhibitors showing lowest enzymatic activity in CIPC and clove during potato storage (LSD (0.05) for treatment = 0.4146 LSD (0.05) for days interval = 0.5863 LSD (0.05) for interaction = 1.3110)
Vertical bars show ±SE of means.
240
(81st day) was found less than that estimated in control on 45th day storage.
Moderate PPO activity observed in spearmint oil application and showed
deviation from clove and CIPC applications after 54rth day storage. CIPC (42.72
U/g) and clove oil (43.94 U/g) applications presented similar PPO activity
through out the storage time with non significant difference recorded between
them.
Enzymatic browning in potato may cause substantial commercial loss and
is primarily associated with the activities of peroxidase and polyphenol oxidase
enzymes (Loaiza and Saltveit, 2001). Nourian et al. (2003) studied transition in
quality attributes and enzyme kinetics in potato stored under different
temperature regimes. He concluded steady increase in PPO activity with the
increase in storage period at ambient temperature. PPO activity remained steady
during 1st month storage in most of the treatments except in hot water treated
potato due to efficient post harvest handling however, increased after ward till the
end of storage. Hot water treatment caused significant reduction in activity during
1st month storage due to enzyme inactivation and thus considered advantageous
in preventing potato browning during subsequent processing. Decline in PPO
activity as result of hot water treatment has also been reported by Yemenicioglu
(2002) in potato, Kim et al. (1993) in apple and Rodriguez-Lopez et al. (1999) in
mushrooms. Decreased PPO activity as results of hot water treatment might be
due to the conversion of oligomeric (active) into monomeric (less active)
configuration which also in lines with the findings of Cho and Ahn, (1999) who
reported de-polymerization of PPO enzyme due to mild heat treatment. Similar
observations regarding reduction in PPO activity has also been reported by
241
Tsouvaltzis et al. (2011) in hot water treated potato slices during storage. The
activity increased steadily afterward in all treatments due to the availability of
substrate and its subsequent oxidation during storage as also reported by the
researcher above. The increased PPO activity in fruits and vegetable during post
harvest storage is also attributed to the moisture loss and senescence (Bryant,
2004) which leads to subsequent sprouting in potato. Our results showed that
high PPO expression closer to potato sprouting might be as a part of plant
defense mechanism and taken as an index of plant response to different stress
conditions which has also reported by Afify et al. (2012). Application of different
anti sprouting agents in the present investigation prevented potato sprouting there
by averted stress conditions consequently presented lower PPO activity as
compare to control during the storage.
4.5.12 Effect on Peroxidase Activity
In response to different anti sprouting agents’ steady increase in
Peroxidase (POD) activity was observed in all the treatments with maximum
activity estimated in control during storage. Treatments means showed maximum
POD activity in T1 while minimum activity observed in T4 and T5 which were
found statistically similar (α-0.05). Storage interval means showed maximum
POD activity at the end while minimum estimated during the start of trial.
Interaction between storage intervals and treatment was significant after 1st
month storage and found highest POD activity in control on D6 onwards till the
end of storage. Irrespective of different treatments the POD activity remained
steady during 1st month storage (Fig. 63).
242
6
13
20
27
34
41
1 9 18 27 36 45 54 63 72 81
Storage Intervals (Days)
PO
D (U
/100
g f.w
)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 63 Per oxidase in response to different sprout inhibitors showing lowest enzymatic activity in CIPC and clove during potato storage (LSD (0.05) for treatment = 0.0966 LSD (0.05) for days interval = 0.3833 LSD (0.05) for interaction = 0.8572)
Vertical bars show ±SE of means.
243
Steady increase in POD activity observed in all the treatments during 1st
month of storage. Unlike PPO, POD activity continued to increase in hot water
treated potato during the storage period with 2-folds estimated at the end of
storage. The over all increase in POD activity was highest (37.83 U/100g) in
control followed by hot water treatment (25.80 U/100g) and found lowest in CIPC
(17.50 U/100g) and clove oil (17.82 U/100g) applications at the end of storage.
Application of spearmint oil as anti sprouting agent presented moderate enzymatic
activity (20.75 U/100g) during the same storage period.
The Increased POD activity is associated with the oxidation of phenolic
compounds under physiological stress causing decay and loss of quality during
storage (Ding et al., 2006). Aydin and Kadioglu, (2001) reported increased POD
activity in fruits and vegetables under stress conditions like progression in their
physiological stages i.e. ripening, senescence which also observed in the present
investigation.
Our results showed in general increased POD activity in all the treatments
as also observed by Nourian et al. (2003) at ambient temperature storage. POD
being more stable in storage atmosphere under stress conditions (Anthon and
Barrett, 2002) showed low percentage increase as compare to PPO. Results also
showed non significant effect of hot water treatment on POD activity which
confirmed the finding reported by Yemenicioglu, (2002). Delaplace et al. (2008)
reported that essential oil application prevent potato from disease incidence due to
their anti viral and anti fungal characteristics. In addition their application prevents
potato sprouting by inhibition of plant growth activities due to their increased
volatility (Arif et al., 2010). In the present study application of different sprout
244
inhibitors effectively prevented potato sprouting as compare to control, and their
lower relative enzymatic activity close to 1st day value might be taken as an index
of better storage stability of potato. Similar enzyme activities in response to
different anti sprouting agents have been reported Afify et al., (2012).
4.5.13 Effect on Chip Moisture Content
Chip moisture contents (CMC) increased with storage time irrespective of
different anti sprouting agent. Treatment means showed maximum moisture
contents in T1 followed by T2 while, T5 followed by T4 retained minimum moisture
contents. Storage interval means showed minimum CMC after the first week while
maximum contents were recorded at the end of storage. The interaction between
treatments and storage intervals was found significant with maximum chip
moisture contents estimated in T1 during last ten days storage (Fig. 64). In general
in all treatments increase in chip moisture contents was found steady and treatment
effect remained statistically less significant till 54rth day storage. The increase in
CMC was highly pronounced in control and hot water treated potato after 63rd and
81st day storage. CMC at the end of storage was found more than 2-folds than that
estimated at the start of experiment. Moderate CMC were estimated in spearmint
oil application at the end of storage however found statistically at par with clove
oil and CIPC applications during most of storage period. Lowest percentage
increase in CMC was estimated in clove oil and CIPC application i.e. 40% and
37% in contrast to 162% increase in control at the end of 81st day storage.
Frying of potato chip is associated with two parallel processes of moisture
loss and fat uptake (Mellema, 2003). During thermal processing of the potato chips
245
1
1.5
2
2.5
3
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Chip
moi
sture
con
tents
(%
)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 64 Chip moisture contents in response to different sprout inhibitors showing highest value in control during potato storage (LSD (0.05) for treatment = 0.03968 LSD (0.05) for days interval = 0.05612 LSD (0.05) for interaction = 0.12550)
Vertical bars show ±SE of means.
246
moisture content present in potato tuber evaporates leaving the structural
reservoirs available for subsequent oil uptake (Basuny et al., 2009). The presence
of high moisture contents in processed potato products are highly undesirable due
to less storage stability and poor sensorial attributes. Potato with intact starch
contents and high specific gravity value were reported to produce potato chips
with low moisture contents (Pinthus et al., 1995). Sprouting in potato tubers are
associated with starch hydrolysis (Biemelt et al., 2000) thus would be producing
chips contents with high CMC and poor sensorial scores. The application of
different anti sprouting agents retained appreciable starch contents thus produced
potato chips with low moisture contents as compare to control. Significant
increase in CMC in control and hot water treated potato due to excessive
sprouting at the end of storage supports significant correlation between these two
phenomenons.
4.5.14 Effect on Chip Fat Absorption
Irrespective of different anti sprouting agents general trend was an
increase in Chip fat absorption (CFA) with storage period. Treatment means
demonstrated significant difference between them with minimum CFA in T5
followed by T4. Maximum CFA was estimated in T1 followed by T2 during the
storage period. The storage interval means showed lowest CFA till 3rd week
storage and found highest at the end. The interaction between storage intervals
and treatment means became highly significant after one month and found
highest CFA in T1 after 2nd month till the end of storage (Fig. 65).
247
Application of different anti sprouting agents presented significant difference in
CFA during the present study. The percentage CFA increase was lower in
different anti sprouting applications like CIPC (24%), Clove oil (25.5%),
spearmint oil (32.1%) hot water treatment (44.5%) in contrast to control
(61.50%) at the end of storage. CIPC and clove oil application were found
equally effective with lowest CFA estimated at the end of storage. The CFA
estimated in CIPC and clove oil applications on 81st day were lower than that
estimated in control on 45th day. Over all control presented highest CFA on 54rth
day with continuous increase till the end of storage.
Fat absorption in potato chips during frying is largely associated with the
starch contents and specific gravity value of the raw material (Kita, 2002). The
onset of sprouting associated with starch hydrolysis resulted in increased fat
absorption in control and hot water treated potato which confirmed the finding of
Biemelt et al. (2000) who reported significant degradation of starch contents in
potato tubers during sprouting in order to provide required energy for sprout
development.
In the present study application of different anti sprouting agents were
found not only effective as sprout suppressants but also exhibited appreciable
retention of starch contents and high specific gravity value. This inverse
relationship between tuber specific gravity and their corresponding fat absorption
during potato processing has also been reported by different researchers like
Basuny et al. (2009), Kita, (2002) and Mehta and Swinburn, (2001).
248
25
30
35
40
45
50
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Chip
fat
abso
rption
(%
)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 65 Chip fat absorption in response to different sprout inhibitors showing highest contents in control during potato storage (LSD (0.05) for treatment = 0.4136 LSD (0.05) for days interval = 0.5850 LSD (0.05) for interaction = 1.3080)
Vertical bars show ±SE of means.
249
4.5.15 Effect on Chip Color
Chip Color (CCL) estimated as approximate L-value showed steady
decrease with the increase in storage time. The treatments means showed highest
CCL value in T5, T4 and T3 and were found statistically similar (at α= 0.05) while
lowest CCL values were identified in T1 followed by T2. Storage interval means
showed maximum CCL values during the first month which afterward declined
steadily till the end of storage. The interaction between treatments and storage
intervals became significant after mid storage with maximum CCL value estimated
at the start and minimum in T1 followed by T2 at the end of storage period (Fig.
66). The application of different anti sprouting agents expressed higher CCL value
as compare to control however the difference between them was less significant.
Statistically the effect of different anti sprouting agents on CCL values remained
similar except some decline expressed in hot water treatment at the end of storage.
Over all the percentage decline in CCL value was found maximum in T1 (20.0%)
followed by T2 (15.3%) at the end of storage period.
Chip Color is the most imperative quality parameter in producer`s
prospective as well sets consumer preference (Segnini et al., 1999). Reducing
sugar contents in potato tubers are key determinant of color development in potato
chip color during frying which is primarily attributed to their participation in
Maillard reaction along with protein fractions (De Wilde et al., 2004).
During the start of experiment irrespective of treatment the CCL values
remained statistically similar however started to decrease with storage time. The
decrease in CCL value was significant in control which might be due to increased
250
50
55
60
65
70
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Chip
col
or (L
-val
ue)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 66 Chip color in in response to different sprout inhibitors showing highest scores in CIPC and clove during potato storage
(LSD (0.05) for treatment = 0.889 LSD (0.05) for days interval = 1.257 LSD (0.05) for interaction = 2.812)
251
starch degradation into monosaccharides due to high sprouting percentage as also
reported by Biemelt et al. (2000). Decreased color scores in control was also
attributed to enzymatic browning at the end of storage period (Mendoza et al.,
2007). The presence of brown spots in potato chips caused poor color scores in
finished product. Another possible reason of low CCL values in control and hot
water treated potato was due to increased fat absorption which conferred oily
appearance on the chip surface. The undesirable color estimation due to increased
fat absorption was also reported by different researchers like Bouchon and Pyle,
(2004) and Rimac-brncic et al. (2004). The application of different anti sprouting
agents were found effective in sprout prevention, starch retention and browning
control thus retained better color scores as compare to control which confirmed the
findings reported by different researchers above.
4.5.16 Effect on Chip Crispiness
Chip crispiness (CCR) scores exhibited initial increase during the start of
storage followed by steady decrease with the progress in storage period. The rate
of decrease in CCR scores was higher in control as compare to all other treatments.
Treatment means revealed non significant difference in T3, T4, and T5 in their CCR
scores with minimum and maximum values estimated in T1 and T6 respectively.
Storage interval means showed highest CCR scores during mid intervals and
lowest at the end of storage. Significant interaction observed between treatments
and storage intervals with maximum CCR scores estimated in T3, T4 and T5 on
36th, 36th and 45th day respectively (Fig. 67). The application of different anti
sprouting agents retained considerable CCR scores till 45th day storage afterward
declined till the end.
252
1
2
3
4
5
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Chip
cri
spin
ess (s
core
s)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 67 Chip crispiness in response to different sprout inhibitors showing highest scores in CIPC and clove during potato storage
(LSD (0.05) for treatment = 0.1062 LSD (0.05) for days interval = 0.1502 LSD (0.05) for interaction = 0.4114)
Vertical bars show ±SE of means.
253
Amongst different treatments percentage decline in CCR scores was found highest
in control (58.4%) followed by hot water treated potato (46.2%). Appreciable CCR
scores were identified in spearmint oil application during most of the storage time
however decreased (3.23/5.00) significantly at the end of storage. CIPC and Clove
oil applications maintained highest CCR scores i.e. 4.00/5.00 and 3.80/5.00
respectively till the end and found statistically similar through out the storage
period.
The particular textural attribute “crispiness” is also synonym for potato
chips i.e. potato crisps is an important quality parameter in setting consumer
preference for processed potato products. Crispiness in potato chips is dependent
on different factors like starch, contents (Kita, 2002), pectin substances (Chang et
al., 1993), fat absorption (Basuny et al., 2009) and superior processing techniques
(Mehta and swinburn, 2001).) The application of different anti sprouting agents
particularly essential oils and CIPC application retained appreciable starch and
pectin contents thus produced potato chips with lower fat and consequent superior
CCR scores as compare to control. The same inverse relationship between chip
crispiness and fat absorption was also reported by Kita et al. (2002). The onset of
sprouting in control resulted in starch hydrolysis and pectin degradation eventually
resulted in decline in textural symmetry and poor CCR scores in potato chips.
4.5.17 Effect on Chip Flavor
Chips flavor (CFL) in general showed an initial increase till mid storage
followed by a progressive decline till the end of storage (Fig. 68). The treatment
means showed minimum CFL scores in T1, followed by T2. T3, T4 and T5 retained
254
highest CFL scores with non significant difference recorded between them. The
storage interval means showed maximum CFL scores during the mid intervals
while minimum were expressed at the end of the storage. The interaction between
storage intervals and treatments showed minimum (1.85/5.00) and maximum
(4.67/5.00) scores in T1 and T3 respectively at different storage intervals (Fig. 68).
Different anti sprouting agents retained appreciable CFL scores till 54rth day
afterward decreased by the end of storage time. The retention of CFL scores were
found highest in CIPC (3.97/5.00) treated potato followed by clove oil (3.77/5.00)
and spearmint oil (3.23/5.00) applications till the end of storage. Highest
percentage decline in CFL scores was observed in control (56.6%) followed by hot
water treated potato (55.5%).
Flavor evolution in potato chips is primarily attributed to the oil uptake and
corresponding volatile formations during thermal processing. The principal factor
effecting Chip flavor are tuber composition, temperature and time of frying, and
frying oil composition (Martin and Ames, 2001). The major aromatic compounds
produced in chip processing are phenyl acetaldehyde, methyl pyrazines, hexanal,
and decadienal (Kondjoyan and Berdague, 1996). The presence of phenolic
compounds, carbohydrates and proteins act as precursor for flavor production in
potato chips during thermal processing (McCann et al., 2010). Application of
different anti sprouting agents showed appreciable flavor scores in potato chips due
to better retention of these organic precursors during storage as compare to control.
255
1
2
3
4
5
1 9 18 27 36 45 54 63 72 81
Storage intervals (day)
Ch
ip f
lavo
r (s
core
s)
Control
Hot water
Spearmint
Clove
CIPC
Fig. 68 Chip flavor in response to different sprout inhibitors showing highest scores in CIPC and clove during potato storage
(LSD (0.05) for treatment = 0.1050 LSD (0.05) for days interval = 0.1485 LSD (0.05) for interaction = 0.3320)
256
4.6 EFFECT OF INTEGRATED TREATMENTS ON THE QUALITY
ATTRIBUTES OF POTATO
In the last phase of study an integrated post harvest management approach
was planned on the basis of results obtained in the 1st and 2nd phase of the study.
Potato variety “lady Rosetta” was treated with hot water (55 ±2oC for 15 minutes)
followed by Clove Oil application (1%). Afterward the tubers were packed in
polypropylene bags and stored at 10 ±1oC temperature and 75± 5% R.H to assess
their eventual post harvest storage life. Physico-chemical and functional assays in
potato tubers were carried out at an intervals of twenty days. In addition, potato
chips prepared from treated potato were coated with different levels of Aloe vera
gel before frying and their subsequent processing attributes were studied at an
interval of thirty days.
4.6.1 Effect on Weight Loss (%)
General trend was increase in weight loss (%) during storage and was
found highly prominent in control than in integrated treatment. Treatment means
illustrated significant difference between them with T1 retained higher weight loss
than T2. Storage interval means showed maximum weight loss on 80th followed by
60th days whereas the minimum weight loss was estimated on 1st day. Interaction
between storage intervals and treatments showed highest weight loss estimated in
T1 on 80th day (Fig. 69).
Weight loss increased with the progression in storage duration however
remained modest during 1st month storage in both treatments. Significant increase
in weight loss experienced in T1 on 40th day (5.86%) and continued to increase
with maximum 12.98% weight loss on 80th day in contrast 2.48% recorded in
integrated treatment during same storage period.
257
0
3
6
9
12
15
1 20 40 60 80 100 120 140 160 180Storage intervals (day)
Wei
ght
loss
(%
)
T1 (Control)
T2 (Treatment)
Fig. 69 Weight loss in response to integrated treatment showing minimum loss as compare to control during storage (LSD (0.05) for treatment = 0.0495 LSD (0.05) for interval = 0.1107 LSD (0.05) for interaction = 0.1566)
Vertical bars show ±SE of means.
258
Weight loss estimated in tubers after that was not carried out due to their
excessive sprout initiation. Integrated treatment effectively reduced weight loss
(%) with steady increase estimated during most of the storage period. In
comparison weight loss (%) estimated in integrated treatment (7.32%) on 180th day
storage was significantly lower than that estimated in control (10.75%) on 60th day.
Potato storage is carried out with strict emphasis on the reduction in weight
loss (%) by preventing excessive respiration. Respiration along with sprouting is
associated with the conversion of valuable starch into soluble sugar which
consequently degraded in to water, carbon dioxide and energy (Fennir, 2002). The
application of different modified atmosphere packaging along with suitable storage
conditions was found effective in reduction in weight loss (%) in horticultural
commodities (Abbasi et al., 2011). Our results showed that the application of
polypropylene packaging (Conte et al., 2009), appropriate storage temperature
(Nourian et al., 2003) and clove oil application (Kleinkopf et al., 2003) prevented
excessive weight loss (%) with ultimate increase in storage stability of potato as
compare to control.
4.6.2 Effect on Total Soluble Solids
General trend showed increase in Total Soluble Solids (TSS) during storage
in both treatments with the increase in storage duration. Treatment means showed
significant difference between them with higher TSS accumulation estimated in T1
as compare to T2. Storage interval means was found significant with lowest TSS
retention on 1st and highest on 80th days. Interaction between treatments and
259
storage intervals was significant with maximum TSS accumulation in T1 on 80th
followed by 60th days (Fig. 70).
TSS increased with the increase in storage duration with highest over all
16.5% increase estimated in control on 80th day. Integrated treatment maintained
lower TSS accumulation during most of the storage period with non significant
increase estimated during 1st month storage. TSS increased steadily afterward with
eventual 6% increase estimated on 180th day. Over all integrated treatment
maintained radically lower TSS as compare to control during storage period.
TSS is associated with increased soluble solids concentration and is
primarily attributed to the soluble sugar contents in fruits and vegetables (Abbasi et
al., 2011). Enzyme mediated conversion of starch into sugar particularly at low
temperature storage and considered highly undesirable for loss of color in
processed potato products (Kumar et al., 2004).
In the present study integrated treatment retained lower TSS contents as
compare to control owing to their reduced rate of respiration under modified
atmosphere packaging and lower temperature storage which confirmed the findings
reported by researchers like Abbasi et al. (2011), Sammi and Masud, (2007),
Nourian et al. (2003) etc. The application of clove oil application prevented the
onset of sprouting which also been related to the increase in starch depletion during
storage hence facilitated lower TSS accumaltion during storage as also been
observed by Sonnewald, (2001).
260
5.4
5.8
6.2
6.6
7
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
Tot
also
lub
le s
olid
s (°
bri
x)
T1 (Control)
T2 (Treatment)
Fig. 70 Total soluble solids in response to integrated treatment showing lower contents as compare to control during storage
(LSD (0.05) for treatment = 0.00577 LSD (0.05) for intervals = 0.01167 LSD (0.05) for interaction = 0.01650)
Vertical bars show ±SE of means.
261
4.6.3 Effect on Sprouting
General trend showed increase in sprouting potential in both treatments
with the increase in storage duration. Treatment means revealed significantly
higher sprouting (%) in T1 as compare to T2. Storage interval means expressed non
significant difference with in 1st, 20th, 100th days, and 140th, 160th, 180th days with
over all maximum percentage estimated in 80th day. The interaction between
treatments and storage intervals was significant with maximum sprouting (%)
estimated in T1 on 80th day (Fig. 71).
Sprouting (%) started to increase in control on 40th day (18.68 %) and
continued at progressive rate till 80th day (92.43%) storage. In contrast integrated
treatment retained complete tuber dormancy till 100 days afterward presented
steady increase in sprouting (%) which remained minimal on 180th day (6.55%)
storage.
Extension in tuber dormancy and reduction of post harvest losses are the
critical factors in potato storage. Sprouting at the end of endo dormancy is one of
the peculiar features of potato (Sonnewald, 2001) which is associated with
substantial economic loss to the grower and processor. Our results showed
remarkable reduction in sprouting (%) in response to integrated treatments as
compare to control. Individual application of hot water treatment followed by
ambient storage (discussed in experiment-2) presented tuber softening however
followed by storage at 10 ±1oC in the present study retained tuber firmness till the
end of storage period. Potato tubers retained intact compositional attributes in
response to hot water treatments, clove oil application, polypropylene packaging,
and storage at 10 ±1oC temperature. The combined effect of these loss reduction
techniques prevented tuber sprouting for six month. The results presented in the
262
0
20
40
60
80
100
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
Sp
rou
tin
g (%
)
T1 (Control)
T2 (Treatment)
Fig. 71 Sprouting in response to integrated treatment showing lower percentage as compare to control during storage (LSD (0.05) for treatment = 0.989 LSD (0.05) for interval = 2.212 LSD (0.05) for interaction = 3.128)
Vertical bars show ±SE of means.
263
present investigation are found in line with the findings of Kyriacou et al. (2008),
Song, (2009) and Knowles et al. (2009).
4.6.4 Effect on Glucose
Data pertaining to glucose contents showed increasing trend with the
progression in storage period in both the treatments. Treatments means showed
significant difference between them with maximum value estimated in T1. Storage
interval means exhibited non significant difference between 60th and 120th days
while all other differed significantly at 5% level of significance. The interaction
between treatments and storage interval was significant with maximum glucose
contents observed in T1 on 80th day (Fig. 72).
Slow increase in glucose contents observed till 20th day storage in both
treatments there after showed progressive and moderate increase in control and
integrated treatments respectively. Control tubers accumulated maximum glucose
contents (340.13 mg/100g) on 80th day after ward discarded due to excessive
weight loss and increased sprouting. Integrated treatments illustrated slow glucose
accumulation during most of the storage period however retained substantial
ultimate glucose contents (323.33 mg/100g). In comparison glucose contents
estimated in T1 on 80th day were found higher than that quantified in T2 on 180th
day.
Sweetening response of potato tubers is associated with low temperature
(Driskill et al., 2009) and potato sprouting due to rapid starch depletion (Biemelt,
2000) during the storage period. The present study revealed that the steady increase
in glucose contents during storage was largely function of storage duration rather
than storage temperature. Glucose contents started increasing at the onset of
264
0
80
160
240
320
400
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
Glu
cose
(m
g/10
0g)
T1 (Control)
T2 (Treatment)
Fig. 72 Glucose in response to integrated treatment showing lower contents as compare to control during storage (LSD (0.05) for treatment= 3.327 LSD (0.05) for interval= 6.773 LSD (0.05) for interaction= 9.579)
Vertical bars show ±SE of means.
265
Sprouting and tuber senescence (Sonnewald, 2001) which was highly significant in
control than integrated treatment. Integrated treatments affectively retained low
sugar accumulation during most of the storage duration. Storage at 10 ±1oC
temperature was found tolerant enough for potato tubers against low temperature
sweetening. The use of polypropylene packaging (Calderon, 2008) along with
clove oil application (Song, 2009) prevented weight loss and tuber sprouting
respectively there by prevented tubers from senescence sweetening (Kumar et al.,
2004) which confirmed the results reported by previous researchers as above.
4.6.5 Effect on Total Sugar
General trend was an increase in total sugar contents with the progression
in storage period. Treatment means showed significant different between them
with T1 retained higher total sugar contents than T2. Storage interval means also
demonstrated significant difference with maximum sugar contents estimated on
180th day and minimum at the start of experiment. Interaction between treatments
and storage intervals was significant with maximum sugar contents identified in T1
followed by T2 on 80th and 180th days respectively (Fig. 73).
Total sugar contents in potato are present primarily in the form of glucose,
fructose and sucrose produced as a result of starch degradation during storage
(Knowles et al., 2009). Reducing sugars like glucose and fructose reported to
participate directly in mallaird browning where as sucrose acts as transient balance
in starch breakdown thus both confer significant commercial loss in potato
(Kyriacou et al., 2009). Sugar accumulation became more significant at low
temperature due to cold induced sweetening hence identification of
266
850
950
1050
1150
1250
1350
1450
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
Tot
al s
uga
rs (
mg/
100g
)
T1 (Control)
T2 (Treatment)
Fig. 73 Total sugar in response to integrated treatment showing lower contents as compare to control during storage
(LSD (0.05) for treatment= 6.85 LSD (0.05) for interval= 15.46 LSD (0.05) for interaction= 21.87)
Vertical bars show ±SE of means.
267
critical temperature for the storage of selected variety is very important (Kumar et
al., 2011). Though the sugar metabolism is primarily associated with the storage
temperature however its elevated concentration has also been reported in potato
tuber close to sprouting (Fauconnier et al., 2002). The application of integrated
treatments prevented accumulation of sugar contents during storage along with
positive varietal response to the storage temperature (10 oC) and anti sprouting
agent (clove oil). The selected temperature and anti sprouting agents maintained
significantly lower sugar contents as compare to control. Considerably higher
sugar contents in control might be due starch degradation trailed by tuber
senescence and increased sprout percentage during storage which was also
reported by Fauconnier et al. (2002) and Swokinose, (1990).
4.6.6 Effect on starch
Starch contents in general showed decreasing trend with the increase in
storage duration in both treatments studied. Treatments means revealed significant
difference between their starch contents with T2 retained higher contents than T1.
Storage interval means showed significant difference in their starch contents with
maximum and minimum values estimated during the start and the end of
experiment respectively. The interaction between treatments and storage intervals
was also significant with lowest starch contents estimated in T1 on the 80th day of
storage (Fig. 74).
Amongst both treatments starch contents decreased with the progression in
storage period however the decrease was more rapid in control than that observed
in integrated treatment. Steady increase and decrease in starch content was
estimated in T2 and T1 respectively on 20th day.
268
15
16
17
18
19
20
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
Sta
rch (g/
100g
)
T1 (Control)
T2 (Treatment)
Fig. 74 Starch in response to integrated treatment maintaining higher contents as compare to control during storage (LSD (0.05) for treatment= 0.0466 LSD (0.05) for interval= 0.1044 LSD (0.05) for interaction= 0.1476)
Vertical bars show ±SE of means.
269
Afterward steady and progressive decline was observed in integrated treatment and
control correspondingly during the rest of the storage period. The highest
percentage decline (18%) was observed in control on 80th day whereas the ultimate
percentage decline in integrated treatment was 12.5% on 180th day.
. Starch is the principal carbohydrate present in potato and governs the
physical quality attributes of potato like specific gravity, dry matter etc (Singh et
al., 2008). Potato tuber is not an inert body owing to its continuous conversion of
starch in to soluble sugars during storage. Starch depletion along with concurrent
sugar accumulation is extremely undesirable post processing disorder being faced
by the processor during potato storage (Tamaki et al., 2003). The energy required
by the dormant tuber during sprouting largely dependent on their starch
degradation (Biemelt et al., 2000). In the present investigation starch depletion in
control tubers might be due to increased respiration rate and sprout initiation.
Integrated treatment offered modified atmosphere packaging to restrain respiration
rate (Conte et al., 2009) augmented by suitable temperature storage (Karim et al.,
2008) and anti sprouting agents (Frazier et al., 2004) there by retained intact starch
contents as compare to control.
4.6.7 Effect on Ascorbic Acid
General trend showed decrease in ascorbic acid (AA) contents during
storage in both treatments. Treatment means showed significant difference
between their ascorbic acid contents with integrated treatment retained higher AA
contents as compare to control. Storage interval means illustrated significant
difference between them with maximum and minimum AA contents estimated at
270
the start and end of storage period respectively. The interaction between treatments
and storage interval was significant with lowest AA contents identified in T1 at the
end of storage period (Fig. 75).
Reduction in ascorbic acid was rapid and steady in control and integrated
treatment respectively. The ultimate percentage decline in AA contents was 41.1%
in T1 on 80th day while 13.8% decline observed in T2 during the same storage
period. Percentage decline in AA contents in integrated treatments remained steady
(23.68%) till 140th day storage there after showed significant eventual decline
(35.28%) at the end of storage period.
Fruits and vegetables are the rich source of dietary anti oxidant vitamin i.e.
ascorbic acid which has vital significance in human metabolism during collagen
formation and immune stimulation (Dale et al., 2003). Owing to its susceptibility
to light and heat the assured presence of this anti oxidant during post harvest
storage is of principal importance (Larisch et al., 1996). Ascorbic acid decline in
both treatments showed that decrease was not only the function of storage
conditions but also due to storage time. Prominent AA contents decline in control
might be attributed to the rapid oxidation of ascorbic acid into dehydro-ascorbic
acid (Blenkinsop et al., 2002) and accelerated due to increased weight loss at
ambient temperature. Intergrated treatment retained appreciable AA contents
during most of the storage period as compare to control. The maximum retention
of ascorbic acid contents might be attributed to modified atmosphere packaging
during the storage period which conferred barrier properties to gaseous exchange
271
14
16
18
20
22
24
26
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
Asc
orb
ic a
cid
(m
g/10
0g)
T1 (Control)
T2 (Treatment)
Fig. 75 Ascorbic acid in response to integrated treatment maintaining higher contents as compare to control during storage
(LSD (0.05) for treatment= 0.1082 LSD (0.05) for interval= 0.2420 LSD (0.05) for interaction= 0.3422)
Vertical bars show ±SE of means.
272
resulted in limited oxidation of ascorbic acid as also reported by Conte et al.,
(2009). In addition temperature management in integrated treatment slowed down
the cellular metabolism consequently retained substantial AA contents during
storage. Similar results regarding higher retention of ascorbic acid at lower
temperature were reported by Nourian et al. (2003), Rivero et al. (2003) and
Davies et al. (2002).
4.6.8 Effect on Chlorophyll
General trend was increase in chlorophyll contents with the increase in
storage period in both treatments. Treatment means illustrated higher chlorophyll
contents in T1 as compare to T2 during storage. Storage intervals means
demonstrated significant difference in their chlorophyll contents with maximum
value quantified on 180th day. The interaction between treatments and storage
intervals was significant with lowest contents estimated at the start of storage in
both treatments while highest contents observed in T1 at the end of storage period
(Fig. 76).
Chlorophyll contents continued to increase in both treatments during
storage. The increase was significant in control on 40th day onward with 3-folds
increase estimated at the end of storage. Increase in chlorophyll contents remained
non significant in integrated treatment during initial 60 days there after showed
slow increase till the end of storage period. The notable increase observed in
integrated treatment was 2-folds, 2.5-folds and 2.7-folds on 140th, 160th and 180th
days respectively.
Post harvest potato greening is an important phenomenon associated with
the concomitant increase of chlorophyll during storage. Green colored tubers
generally perceived as low quality products due to greening, discoloration and
273
0.4
0.8
1.2
1.6
2
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
Ch
loro
ph
yll (
mg/
100g
d.w
T1 (Control)
T2 (Treatment)
Fig. 76 Chlorophyll in response to integrated treatment maintaining lower contents as compare to control during storage
(LSD (0.05) for treatment = 0.02334 LSD (0.05) for interval = 0.05218 LSD (0.05) for interaction = 0.07380)
Vertical bars show ±SE of means.
274
increased incidence of glycoalkaloid contents (Nema et al., 2008). Results
expressed in present study concluded that integrated treatments accumulated lower
chlorophyll contents as compare to control consequently presented less tuber
discoloration. Dark potato storage supplemented with modified atmosphere
packaging (Rosenfield et al., 1995) suitable temperature management (Nourian et
al., 2003) and appropriate sprout inhibition ((Kleinkopf et al., 2003) found
valuable in efficient potato storage for six months. Increased chlorophyll contents
with subsequent discoloration in control reduced the over all tuber quality which
confirmed the results presented by Rita et al. (2007) Grunenfelder et al. (2006) and
Percival, (1999).
4.6.9 Effect of integrated treatment on Total Glycoalkaloids
Total glycoalkaloids (TGA) in general showed gradual increase in both
treatments with the progress in storage duration. Treatment means illustrated
significant difference between them with T1 accumulated higher TGA contents.
Non significant difference was observed between 60th and 140th days while all
other Storage interval remained statistically different at α-0.05. The interaction
between treatments and storage intervals was significant with maximum TGA
contents quantified in T1 on 80th day (Fig. 77).
TGA contents increased in both treatments with higher accumulation
estimated in control than the integrated treatment. The initial increase estimated in
TGA contents was around 2-folds on 20th day storage and remained relentless with
eventual more than 12-folds increase estimated on 80th day storage. The final TGA
contents quantified (86.23 mg/100g D.W) in control potato exceeded the safe limit
prescribed for human intake.
275
0
20
40
60
80
100
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
TG
A (
mg/
100g
d.w
)
T1 (Control)
T2 (Treatment)
Fig. 77 Total Glycoalkaloids in response to integrated treatment maintaining lower contents as compare to control during storage
(LSD (0.05) for treatment= 0.689 LSD (0.05) for interval = 1.492 LSD (0.05) for interaction = 2.111)
Vertical bars show ±SE of means.
276
Integrated treatment retained moderate TGA contents during most of the storage
period with eventual 7-folds increase on 180th day. In comparison TGA contents
quantified in control on 60th day were higher than that estimated in integrated
treatment at the end of six month storage.
Increased world over consumption of potato focused the attention of
researchers regarding the presence of its toxic glycoalkaloids. Small amount of
TGA contents in potato reported to improve flavor however their increased level
above 28mg/100g f.w can bring about possible lethal consequences (Nema et al.,
2008). Post harvest storage of potato is usually accompanied with the simultaneous
increase in TGA contents during storage as also observed in the present study.
Biosynthesis of TGA is independent however known to be associated with tuber
sweetening (Percival, 1993), greening (Rita et al., 2007) and sprouting (Sengul et
al., 2004). Integrated treatments retained lower TGA accumulation and improved
storage stability as compare to control owing to their improved packaging system,
apt storage temperature with apposite anti sprouting agents which was in line with
the findings of researchers like Rosenfeld et al. (1995) and Nema et al. (2008),
4.6.10 Effect on Total Phenolic Contents
General trend was initial increase in total phenolic contents (TPC) followed
by gradual decline with the increase in storage period. Treatment means
demonstrated that T2 retained higher TPC as compare to T1. Storage interval means
showed significant difference between them with highest TPC estimated on 20th
and 100th days with non significant difference found in between them. The
interaction between treatments and storage intervals was found significant with
maximum TPC observed in T2 on 80th day (Fig. 78).
277
TPC increased in control till the mid storage afterward showed progressive
decline till the end. The percentage increase and decrease in TPC in control
remained around 40% and 32% respectively during 80 days storage. TPC
continued to increase in integrated treatment till 80th day there after showed decline
till the rest of storage period. The percentage increase and decrease in TPC in
integrated treatments remained about 50% and 13% respectively during 180 days
of storage. In comparison the maximum TPC quantified in control on 40th day
remained statistically similar to those observed in integrated treatment on 100th day
storage.
Total phenolic contents are one of the most commonly occurring
bioactive plant secondary metabolite synthesized during shikimate and acetate
pathways (Bravo, 1998). They are amongst the major antioxidants reportedly
present in potato along with ascorbic acids, carotenoids, tocopherols etc.
(Reyes and Zevallos, 2003). Despite of carrying modest TPC contents potato
showed significant inhibition of low density lipoprotein oxidation (Vinson et
al., 1998). Phenolic contents known to increase during the post harvest
storage of potato however found susceptible to the activities of enzymes like
polyphenol oxidases and peroxidase (Vitti et al., 2011). Our results showed
that integrated treatments retained appreciable TPC during most of the storage
period as compare to control. Modified atmosphere packaging along with low
temperature storage prevented the oxidative degradation of TPC during
storage. Maintaining tuber dormancy as results of different anti sprouting
agents also kept tubers out of physiological stress imposed by polyphenol
oxidases thus retained appreciable TPC as compare to control.
278
60
80
100
120
140
160
180
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
TP
C (
mg
GA
E/1
00g
d.w
T1 (Control)
T2 (Treatment)
Fig. 78 Total phenolic contents in response to integrated treatment maintaining higher contents as compare to control during storage (LSD (0.05) for treatment= 1.918 LSD (0.05) for interval= 3.795 LSD (0.05) for interaction= 5.368)
Vertical bars show ±SE of means.
279
The results expressed are in line with the observations reported by
Madiwale et al. (2011), Barberan and Espin, (2001) and Saltveit, (2000)
regarding the post harvest stability of Total Phenolic Contents under improved
storage conditions.
4.6.11 Effect on Radical Scavenging Activity
In general radical scavenging activity (RSA) showed initial increase
followed by gradual decrease in both treatments with the progression in
storage period. Treatment means illustrated significant difference between
them with higher activity estimated in T2 as compare to T1. Storage interval
means showed significant difference between them with maximum activity
quantified in T2 on 100th day. The interaction between treatments and
storage intervals was significant with T2 retained utmost activity during most
of the storage period with lowest activity estimated in T1 at the end of
storage (Fig. 79).
Increase in radical scavenging activity remained statistically
significant in both treatments on 20th day storage. RSA significantly
decreased afterward on 80th day in control expressing 50% decline from the
terminal value (41.50%) estimated during the storage. Integrated treatments
retained appreciable RSA during most of the storage period. The activity
continued to increase on 60th day (45.73%) and remained statistically same
onward till 100th day (44.47%) storage. Progressive decline in RSA observed
afterward with minimum value estimated at the end (23.50%).
280
15
20
25
30
35
40
45
50
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
RSA
(%
)
T1 (Control)
T2 (Treatment)
Fig. 79 Radical scavenging activity in response to integrated treatment maintaining higher activity as compare to control during storage (LSD (0.05) for treatment= 0.462 LSD (0.05) for interval= 1.025 LSD (0.05) for interaction= 1.449)
Vertical bars show ±SE of means.
281
Radical scavenging activity in potato tubers corresponds to their antioxidant
potential. Anti oxidant compounds present either as enzymatic or non-
enzymatic known to inhibit substrate oxidation and quench free radical
produced in biological system (Arnao, 2000). Enzymatic and non-enzymatic
antioxidants are required for intracellular and extracellular defenses against
different oxidants produced during cellular metabolism.
The radical scavenging activity estimated in the present study is
primarily related to the non-enzymatic anti oxidants. Retention of significant
antioxidant potential in potato thus required for its storage stability and
valuable functional potential. The increased activity during the initial
storage period in potato tubers might be attributed to their high ascorbic
acids and phenolics contents (Blessington et al., 2007). The significant
correlation between radical scavenging activity and phenolic compounds has
been reported by different researchers like Abbasi et al. (2011) and Lachman
et al. (2008).
Integrated treatment retained appreciable antioxidant activity during
most of the storage period as compare to control. The increased activity
under modified atmosphere storage (Piga et al., 2002), appropriate storage
temperature (Lewis et al., 1999) in the presence of suitable sprout inhibitors
(Bajji et al., 2007) has been reported by several researchers which verified
the facts framed in the present study. Eventual decline in activity might be
attributed to the loss of ascorbic acids along with increased polyphenol
oxidase activity under prolonged storage as observed by Davies et al.
(2002).
282
4.6.12 Effect on Polyphenol Oxidase (PPO) Activity
Polyphenol activity (PPO) in response to integrated treatments (T2) retained
lower PPO activity during storage in contrast significant activity was observed in
control (T1) (Fig. 80). Treatment means showed lower PPO activity in integrated
treatment and higher in control during storage. Storage interval means showed
significant difference in their PPO activity with maximum activity observed on
80th day. Non significant difference observed between 1st, 20th and 180th days
during the storage period. The interaction between treatment and storage intervals
was highly significant with maximum value recorded in T1 on 80th day (Fig. 80).
PPO activity increased in control with the progression in storage period.
The activity remained steady till 20th day there after increased progressively upto
80th day. The PPO activity in control was not estimated afterward because of
excessive sprouting due to dormancy break. The over all increase in PPO activity
remained around 2.5 folds than that estimated on the 1st day of storage. In contrast
significant decline in PPO activity was illustrated by integrated treatments.
Percentage decline in PPO remained highest on 20th day (23.6%) afterward
increased steadily till remained below the activity (30.47 U/g) observed in the start
of experiment.
Polyphenol oxidases are the metalloenzymes which catalyzes oxidation of
phenols into quinines and subsequent brown colored melanin formation (Afify et
al., 2012). The enzymes are associated with plant response under different stress
conditions and taken as an index of post harvest life in horticultural commodities.
High PPO activity observed in control might be associated with the tuber sprouting
283
20
30
40
50
60
70
80
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
PP
O (
U/g
f.w
)
T1 (Control)
T2 (Treatment)
Fig. 80 Polyphenol oxidase in response to integrated treatment showing lower enzymatic activity as compare to control during storage (LSD (0.05) for treatment = 0.347 LSD (0.05) for interval = 0.776 LSD (0.05) for interaction = 1.097)
Vertical bars show ±SE of means.
284
and physiological stress imposed due to senescence (Byrant, 2004). Integrated
post harvest management of potato tubers under storage retained lower PPO
activity even after 180 days storage. Application of hot water treatment was
found effective in the partial inactivation of this enzymes as also been observed
by Yemenicioglu, (2002). The application of improved packaging materials i.e.
polypropylene (Kader, 2002), appropriate temperature management i.e. 10oC
(Nourian et al., 2003), suitable sprout inhibitors i.e. Clove oil (Arif et al., 2010)
maintained low PPO activity consequently presented prolonged storage stability
(180 days) of potato tuber as compare to control (80 days).
4.6.13 Effect on PerOxidase (POD) activity
In response to the application of integrated treatment (T2) POD activity
decreased in potato tubers while parallel increase was observed in control (T1).
Treatment means showed significant difference between them with T1 retained
higher POD activity than T2. Storage interval means exhibited significant
difference in their POD activity with maximum value estimated on 80th day. The
interaction between treatments and storage interval was significant with
maximum value identified in T1 during most of their storage period (Fig. 81).
POD activity continued to increase in control with no sign of termination
till the on set of sprouting at the end of storage. The significant increase in POD
activity witnessed on 40th day (21.17 U/100g) storage onward and ended with
more than 3-folds increase on the 80th day (77.03U/100g). POD activity declined
significantly in response to integrated treatment applied through out the storage
period. Like poly phenol oxidase activity decline in per oxidase activity also
observed till 80th day storage (9.10 U/100g) there after showed moderate rise till
285
8
16
24
32
40
1 20 40 60 80 100 120 140 160 180
Storage intervals (day)
PO
D (
U/1
00g
f.w
)
T1 (Control)
T2 (Treatment)
Fig. 81 Per oxidase in response to integrated treatment showing lower enzymatic activity as compare to control during storage (LSD (0.05) for treatment= 0.2054 LSD (0.05) for interval = 0.4594 LSD (0.05) for interaction = 0.6497)
Vertical bars show ±SE of means.
286
180th day (11.40 U/100g). The final POD activity remained below the value
estimated before the start of experiment on 1st day.
Peroxidases (POD) and polyphenol oxidases (PPO) are considered as the
major enzymes responsible for quality loss in potato due to phenol degradation
(Francois and Espin, 2001). The estimation of these enzymes during post harvest
storage of horticultural produce presents reasonable assumption for their eventual
storage stability. The decrease in POD activity in integrated treatments might be
attributed to the lower temperature storage (10oC) as compare to control. In
addition the application of polypropylene packaging with clove oil application
conferred barrier properties with sprout inhibition eventually maintained tuber
dormancy up to 180 days as compare to 80 days observed in control. The efficient
storage stability of potato tubers under different integrated post harvest treatments
is also reported by researchers like Nourian et al. (2003), Delaplace et al. (2010)
and Afify et al. (2012).
4.6.14 Effect on Chip Moisture Contents
In general pre processing application of different concentrations of Aloe
Vera (A.V) on the potato chip showed increase in Chip Moisture Contents.
Treatment means showed significant difference between them with maximum
CMC observed in T4 and minimum in T1. Storage interval means showed
significant difference between them with maximum CMC estimated on 180th day.
The interaction between treatments and storage intervals was found significant
with maximum CMC quantified in T4 at the end of storage period (Fig. 82). CMC
increased with the increase in the concentration of A.V coatings during the storage
period.
287
0
3
6
9
12
15
1 30 60 90 120 150 180
Storage intervals (day)
Ch
ip m
oist
ure
con
ten
t (%
)
Control
A.V 10%
A.V 20%
A.V 30%
Fig. 82 Higher Chip moisture content in potato chips due to aloe vera (A.V) coatings as compare to control
(LSD (0.05) for treatment = 0.1600 LSD (0.05) for interval = 0.2117 LSD (0.05) for interaction = 0.4234)
Vertical bars show ±SE of means.
288
The increase in CMC in A.V 10%, A.V 20% and A.V 30% remained around 8.1
folds, 9-folds and 11.1-folds after 180 days storage. In contrast the increase in
control remained less than 2-folds during the same storage period.
Pre processing chip moisture contents is directly proportional to the post
processing fat absorption. Surface properties of frying raw material are very
important to establish eventual fat absorbed during processing. Modification in
these surface coatings may be carried out by the application of different edible
coating which can be transparent or thick like batter (Mellema, 2003). In doing so
uniform coating configuration on the surface is imperative to bound mass transfer
during processing (Huse et al., 1998). Garmakhany et al. (2008) also evaluated
quality attributes of potato chips in response to different hydrocolloid
applications.
Different coating materials i.e. carboxy methyl cellulose, xanthan, and
guar were applied in selected concentrations before processing. He concluded all
the coating materials retained comparatively high moisture contents and reduced
fat absorption as compare to control. Our results showed that increasing A.V
concentration resulted in increased CMC after processing with similar pattern
observed with the progression in storage period. Similar observations were
reported by Khalil, (1999) regarding the increased moisture contents in French
fries in response to increased coating concentration. The appropriate
concentration of coating material however must be established in order to prevent
sogginess and reduced sensorial scores as happened in T4 (A.V 30%) during the
last month of storage.
289
4.6.15 Effect on Chip Fat Absorption
Chip fat absorption (CFA) decreased with the progression in storage
period in all the treatments except in control. Treatments means revealed
significant difference between them with maximum and minimum CFA estimated
in T1 and T4 respectively. Non significant difference observed between 30th and
60th days while all other storage intervals differed significantly with each other.
The interaction between treatment and storage interval was significant with
maximum CFA estimated in T4 during most of the storage period (Fig. 83).
Amongst different treatments concentrations of Aloe vera showed significant
reduction in CFA along the storage period. The percentage reduction in CFA on
20th day remained around 13.4%, 20.5% and 23.1% in T2 (A.V 10%), T3 (A.V
20%), and T4 (AV 30%) respectively in contrast slight increase in CFA observed
in control. With in different storage intervals CFA increased amongst all the
treatments with lowest CFA observed in T4 (27.53%) followed by T3 (27.98%)
while maximum CFA estimated in T1 (37.00 %) on 180th day storage.
Potato chip is preferred snack food liked all over the world due to its
unique sensorial attributes. The intake of this quality food product is how ever
associated with high fat intake thus largely contributing towards obesity and
coronary heart disorders (Mellema, 2003). In addition to different techniques
employed to reduce eventual fat absorption hydrocolloids application has been
carried out by different researchers to reduce the fat absorption in processed food
products. The efficiency of these coating materials however depends on their
barrier properties, applied concentration and ability to produce quality finished
290
20
25
30
35
40
1 30 60 90 120 150 180
Storage intervals (day)
Chip
fat
abso
rpti
on (
%)
Control
A.V 10%
A.V 20%
A.V 30%
Fig. 83 Higher Chip fat absorption in potato chips due to aloe vera (A.V) coatings as compare to control
(LSD (0.05) for treatment = 0.1895 LSD (0.05) for interval = 0.2507 LSD (0.05) for interaction = 0.5015)
Vertical bars show ±SE of means.
291
products (Garcia et al., 2002). Our results in the present study showed fat
reduction in processed products in response to different coating concentrations
applied which confirmed the previously reported findings by Rimac-Brncic et al.,
(2004), Albert and Mittal, (2002) and Rayner et al. (2000). The significant
increase in CFA along the storage intervals in different treatments might be
associated with starch degradation which has also been reported by Basuny et al.
(2009), and Kita, (2002).
4.6.16 Effect on Chip Color (CCL)
Chip color estimated as approximate L-value generally decreased with the
increase in storage duration. Non significant difference observed between T2 and
T3 regarding their CCL values with maximum and minimum value estimated in
T1 and T4 respectively. Significant difference between most of the storage
intervals observed with highest and lowest values were estimated at the start and
the end of storage period respectively. Interaction between treatments and storage
intervals was significant with minimum values quantified in T4 during last month
storage (Fig. 84).
L-value decreased in all the treatments with the increase in storage period
with statistically similar value recorded during most of the storage period.
Maximum color values were identified in control during most of the storage
period with lowest percentage decrease (6.1%) estimated on 180th day storage. In
contrast the percentage decrease in L- value remained higher in coated chips with
utmost decline observed in T4 (10.7%) during the same storage time. In terms of
L-value, T2 and T3 remained statistically similar through out the storage period
with 8.7% decline observed in each treatment till the end of storage period.
292
56
58
60
62
64
66
1 30 60 90 120 150 180
Storage intervals (day)
Col
or (L
-val
ue)
Control
A.V 10%
A.V 20%
A.V 30%
Fig. 84 Comparision of Chip color in response to aloe vera (A.V) coatings on potato chips (LSD (0.05) for treatment = 0.910 LSD (0.05) for interval = 0.425 LSD (0.05) for interaction = 2.408)
Vertical bars show ±SE of means.
293
L-values correspond to the lightness of chip color which is primarily
associated with the consumer acceptance (Mendoza et al., 2007). In the present
study CCL values affected by different coating applications and decreased with
the increase in the applied concentrations. For instance chips coated with 10 %
A.V (T2) and 20% A.V (T3) retained high L-values than those coated with 30%
A.V (T4) coating. Similar results were reported by Khalil, (1999) who reported
decreased color values in French fried due to calcium chloride application at
increased concentration. Our results revealed that increase in A.V concentration
maintained appreciable L-value up to some threshold level (10-20%) however
exhibited considerable decline (30%) as a consequence of excess application as
also reported by the researcher above. Coating application prior to frying in
potato products has been reported to decrease likely acrylamide formation in
processed products (Fiselier et al., 2004).
In the present study retention of appreciable CCL scores as results of
different coating (A.V-10%, A.V-20%) might also be associated with their
reduced acrylamide formation. Similar observation regarding reduction of
acrylamide contents as results of pre processing coating applications has been
reported by Vattem and Shetty (2003). The steady decline in L-values in all the
treatments along storage period might be attributed to their increased reducing
sugar contents as also been observed by Biedermann-Brem et al. (2003) and
Blenkinsop et al. (2002).
4.6.17 Effect on Chip Crispiness
Chip crispiness scores showed initial increase till the mid storage
followed by gradual decline at the end. Treatment means showed significant
difference between their CCR scores with maximum estimated in T3 followed by
T2. Non significant difference was observed between 30th and 120th days while all
other intervals were significantly different at 5% level of significance.
294
3
3.5
4
4.5
5
1 30 60 90 120 150 180
Storage intervals (day)
Ch
ip c
risp
ines
s (s
core
s)
Control
A.V 10%
A.V 20%
A.V 30%
Fig. 85 Comparision of Chip crispiness in response to aloe vera (A.V) coatings on potato chips (LSD (0.05) for treatment = 0.0677 LSD (0.05) for interval = 0.0896 LSD (0.05) for interaction = 0.1792)
Vertical bars show ±SE of means.
295
The interaction between treatments and storage intervals was significant with
maximum CCR scores quantified in T3 during most of the storage period (Fig.
85). Remarkable CCR scores were identified in low and moderate A.V coatings
during the storage period. Aloe Vera at 20% concentration presented best CCR
scores through out the storage period however remained statistically similar to
10% application during most of the storage period. Significant decline in CCR
scores was observed in 30% application during the last month of storage period.
Crispy texture is the hallmark attribute of potato chips which is believed
to be associated with the dry matter present in raw material. Starch and
protopectin are the most imperative chemical component contributing to quality
chip texture (Kita, 2002). Textural attributes reported to be effected by the
application of different coatings due to modification of surface properties
(Mellema, 2003). Application of 20% Aloe vera presented remarkable chip
texture during frying while inferior CCR scores were quantified in Aloe vera
30% which might be due to their increased moisture retention which
subsequently caused sogginess after processing (Pedreschi and Mayano, 2005).
Superior maintenance of textural attributes with acceptable scores due to
hydrocolloid coating have also been reported by researchers like Khalil (1999),
Kita, (2002) and Garcia et al. (2002).
4.6.18 Effect on Chip Flavor
Chip flavor scores in general illustrated gradual initial increase followed
by decline at the end of storage period. Treatment means showed significant
difference between their CFL scores with maximum CFL scores observed in T1.
followed by T3. Non significant difference observed between most of the storage
intervals with lowest CFL scores estimated on 180th day. Interaction between
296
3
3.5
4
4.5
5
1 30 60 90 120 150 180
Storage intervals (day)
Chip
fla
vor
(sco
res)
Control
A.V 10%
A.V 20%
A.V 30%
Fig. 86 Comparision of Chipflavor in response to aloe vera (A.V) coatings on potato chips
(LSD (0.05) for treatment = 0.1016 LSD (0.05) for interval = 0.1344 LSD (0.05) for interaction = 0.2688)
Vertical bars show ±SE of means.
297
treatments and storage interval was significant with lowest scores identified in T4
at the end of storage period (Fig. 86). Significant decline in CFL scores was
observed in T4 (A.V 30%) after mid storage period with minimum scores
(3.10/5.00) identified on 180th day. T2 (A.V 10%) and T3 (A.V 20%) maintained
appreciable flavor scores during most of the storage period with 3.64/5.00 and
3.78/5.00 CFL scores respectively estimated at the end of storage. Control
retained maximum flavor scores through out the storage period with 4.04/5.00
CFL scores identified at the end of storage period.
Flavor is the combined sensation derived from the senses of taste and
aroma. In general hydrocolloid coatings presented lower CFL scores as compare
to control. Maximum CFL scores were estimated in control during most of the
storage period which might be attributed to their high fat absorption during
processing. Frying oil importance as flavor precursor has also been reported by
Martin and Ames, (2001). Garcia et al. (2002) evaluated the efficiency of
different cellulose based edible coatings in reduction in oil absorption during
processing. He concluded that the combination of 1% methyl cellulose and 0.5%
sorbitol proved to be most efficient coating for fat reduction and flavor retention
in potato chips. In the present study Aloe vera coatings except in 30% application
presented appreciable CFL scores during chip processing which also of great
significance because of no coating based off flavor development identified by the
judges during evaluation. A.V (30%) presented lowest flavor scores due to bitter
after taste and increased moisture contents in processed chips. It was eventually
concluded that A.V (20%) retained all the chip sensorial attributes owing to its no
after taste and off flavor development along with lowest chip fat absorption.
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GENERAL DISCUSSION
Potato is a delicious, highly nutritive vegetable extensively being consumed
all over the world in variety of food preparations. Presence of low cholesterol and
significant ascorbic acids and phenolic contents confer momentous funtional
potential to this vegetable. The crop is however facing different physiological
disorders like greening, alkaloidal toxicity, cold sweetening and sprouting during
its post harvest storage. In addition acrylamide formation in thermally processed
potato products is of grave food safety concern. The study was therefore designed
to optimize different storage conditions (packaging, light, temperature, sprout
inhibitor) to ensure regular supply of premium potato variety for the local potato
industry with the use of cheap, natural and safe technologies.
In the first phase of the study “Lady Rosetta” presented best overall
characteristics amongst the tested varieties due to its suitable size and sphericity,
low sprout (%), high dry matter, low fats and reducing sugar contents, significant
functional potential and above all the remarkable processing performance. Atlantic
and Hermes were also impressive owing to their high dry matter contents, long
dormancy period and impressive processing performance however outstanding
functional potential has been identified in the Desi variety. The study also invoked
significant correlations between different quality attributes studied in the selected
potato varieties (Table 2b, 4b).
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In order to optimize the storage conditions for the premium potato variety
the second phase of the study was divided into four different experiments to
evaluate the effect of different packagings, light sources, temperature regimes and
sprout inhibitors on the selected quality attributes. In general weight loss, total
soluble solids, glucose, total sugars, glycoalkaloids, chlorophyll, polyphenol
oxidase, peroxidase, increased while pH, specific gravity, starch and ascorbic acids
decreased with the progression in storage period. Total phenolic contents and
radical scavenging activity showed a sort of parabolic trend during the storage
period. Post processing parameters like chip moisture contents, chip fat absorption
increased while sensorial attribute exhibited gradual decrease along the storage
period. In spite of this general trend, significant divergences were observed with in
different treatments and storage conditions in the studied quality attributes.
Weight loss (%) was found maximum in control however the use of poly
propylene and LDPE packaging, dark potato storage and application of essential
oils as sprout inhibitors proved to be vital tool in preventing potato dehydration
during storage. Temperature management below 15 oC presented minimum weight
loss (%) amongst all the storage conditions studied which might be due to the
reduced respiration rate at low temperature (Kyriacou et al., 2009). Total soluble
solids (TSS) increased during the storage period due to hydrolytic conversion of
starch in to soluble sugars (Kittur et al., 2001). Packaging like polypropylene and
LDPE, dark storage and sprout inhibitors maintained slower increase in total
soluble solids as compare to control. Low temperature storage provoked significant
increase in the TSS contents which might be mediated due to the phenomenon of
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cold sweetening. The final decrease in TSS was also found associated with potato
sprouting (%) due to the rapid utilization of soluble sugars by growing sprouts as
also reported by Sowokinose, (1990).
Significant correlation was reported between specific gravity and starch
contents of potato by several researchers (Kazami et al., 2000, Kumar et al., 2004)
which remained consistent in the present study under different storage conditions.
After initial increase in the specific gravity and starch contents during early week
of storage the attributes started to decline during storage period. Polypropylene and
LDPE packaging, dark storage and application of sprout inhibitors caused this
decline at slower pace as compare to their respective controls. Starch degradation
at the twilight of the storage was also found closely associated with the appearance
of visible sprouts (Farre et al., 2001). Conversely highly prominent decline was
observed during the early week in these two parameters under low temperature
storage (5 oC).
Predominant sugars produced in the potato are sucrose, glucose and fructose
(Hajirezaei et al., 2003) and showed diverse sugar metabolism specifically under
comparative temperature storage. Packaging like LDPE, polypropylene maintained
controlled sugar accumulation in potato as compare to control. Similar
observations were recorded in response to the different sprout inhibitors and dark
potato storage. Considerable increase in sugar contents were recorded at high
temperature as well as low temperature storage. Storage at 25 oC resulted in the
increase in sugar contents from starch degradation due to senescence sweetening.
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On the other hand the storage at 5 oC triggered significant sugar accumulation due
to the phenomenon of cold sweetening (Tamaki et al., 2003). The study showed
that variety Lady Rosetta was cold susceptible variety and require some critical
storage temperature to avert potato sweetening under prolong storage.
Tuber toxicity due to the presence of total glycoalkaloids (TGA) contents in
potato was also studied under different storage conditions. TGA contents continued
to increase under all storage conditions however the increase was found
proportional to the weight loss (%), high energy light sources, tuber sprouting
(Nema et al., 2008) and high temperature storage. Minimum TGA contents were
identified in packaging, dark storage, low temperature storage and essential oil
applications. Study also revealed high significant correlation between TGA
contents and chlorophyll accumulation in response to exposure to high energy
illuminations like red and blue lights (Table 31, 32).
Ascorbic acid is the predominant organic acid in potato tuber which also
corresponds to its significant radical scavenging activity under DPPH assay
(Nzaramba, 2007). Post harvest profile of potato tuber revealed significant
reduction in ascorbic acid in response to high energy light sources, heat, increased
weight loss (%) and sprouting. Improved packaging like LDPE and polypropylene
retained substantial ascorbic acid contents as compare to control which has also
been reported by (Calderon et al., 2008). Storage at low temperature (5 oC)
retained maximum ascorbic acid during the four month storage however found
detest due to the rapid increase in sugar contents.
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LDPE and polypropylene packaging retained significant total phenolic
contents (Gonzalez et al., 2004) as compare to control. Over all TPC continued to
increase under different storage conditions followed by gradual decline afterward.
The possible reason might be due to the onset of potato browning and sprouting
during the final weeks of storage. On the other hand low temperature (5 oC)
Storage retained maximum TPC during storage period (Lachman et al., 2008).
RSA corresponds to total phenolic contents and ascorbic acid contents present in
the potato tubers. Improved packaging, dark storage, sprout inhibitors and low
temperature storage also maintained appreciable RSA activity as compare to their
respective controls. Highly significant correlation was identified between TPC and
radical scavenging activity (RSA) during the start of potato storage which
decreased after ward due to the loss of ascorbic acid during storage.
PPO and POD continued to decrease under all storage conditions however
the activity of former was found highly prominent during potato post harvest
storage. Packaging reduced the enzymatic activity as compare to control possibly
might be due to substrate inhibition and low phenolic oxidation (Kader, 2002).
Significant reduction in PPO and POD activities were observed at low temperature
(5 oC) storage. PPO activity was found susceptible to potato blanching during hot
water treatment carried out as sprout control while POD activity remained un
deterred which confirmed the findings reported by Yemenicioglu, (2002).
Post processing evaluation of potato chips showed significant association
between chip quality and the composition of potato tubers under different storage
303
conditions. Chip moisture content and chip fat absorption were inversely related
with the specific gravity and starch contents of the raw material as reported by
Mehta and Swinburn, (2001). Chip color and chip texture were found closely
related with the presence of sugar and starch contents respectively (Kita, 2002).
Potato storage at low temperature (5 oC) presented prominent decline in color
scores which might be associated with elevated reducing sugar contents due to cold
sweetening. Polypropylene packaging and potato storage at 15 oC presented
remarkable processed products as compare to control.
In the last phase (3rd phase) of the study the prominent results identified
during different storage conditions were offered in combination to develop an
integrated strategy to conserve these vital quality attributes during the storage. The
strategy comprised of the best packaging material (polypropylene), suitable light
source (dark), optimum storage temperature (10 oC) and appropriate sprout
inhibitors (hot water treatment followed by clove oil application) to access the
storage life with intact quality parameters. Post harvest disorders like alkaloidal
toxicity, cold sweetening, greening, sprouting in potato were efficiently controlled
with out posing any health or environmental hazards. Results showed the
conservation of vital quality attributes and post harvest storage life of potato
variety “Lady Rosetta” was prolonged up to three times as compare to control.
This phase was distinguished with the application of different levels of Aloe vera
prior to potato processing with an objective to produce low caloric HALAL
(permissible food in Islamic jurisprudence) potato product. High chip moisture
contents, appreciable sensorial scores and reduced chip fat absorption were
304
observed as result of different levels of hydro colloidal coatings before processing.
Moreover Aloe vera coating produced potato chip with remarkable color scores
which can also be associated with low perceived acrylamide formation as also been
reported by other researchers like Vattem and Shetty, (2003) and Fiselier et al.
(2004). 20% Aloe vera application proved to be the best vegetable based potato
chip coating with moderate moisture and fat contents and appreciable retention of
sensorial score.
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CONCLUSIVE SUMMARY
Potato is third major staple crop after wheat and rice with increasing total
production witnessed over the last twenty years in developed and under developed
countries. In addition to its table use substantial increase in the consumption of
versatile processed potato products such as, chips, mashed potatoes, baked potato,
tinned potatoes etc. have been observed all around the world. Recognizing the
global importance of this crop with special reference to food security issue in the
third world and densely populated countries, FAO had declared year “2008” as an
International Year of Potato (IYP).
Potato is the premium vegetable crop of Pakistan grown through out the
country with four growing seasons. The bulk of produce however is wasted due to
Poor post harvest management practices results in post harvest storage disorders
like greening, cold induced sweetening, steroidal toxicity, sprouting etc. In
addition limited availability of quality raw material for processing is the main
concerns for the industry. Sighting the above reported problems three-phased
comprehensive study was planned to establish integrated approach for the
prevention of post harvest losses along with intact quality processing attributes in
premium potato variety during storage.
In the 1st phase of study ten commercial potato varieties namely, Agria,
Atlantic, Cardinal, Courage, Chipsona, Desiree, Desi, Hermes, Lady Rosetta and
Satellite were studied for their physical, chemical and functional attributes, with
special reference to their potential in chip processing. In general Lady Rosetta
followed by Hermes was the most appreciable variety regarding their physical
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306
attributes. Lady Rosetta followed by Atlantic attained maximum dry matter and
starch contents. However, least sugar contents were recorded in Agria and
maximum fat and protein contents were found in Desiree. Significant correlation
(R= 0.986) was estimated between dry matter and starch contents. Amongst tested
varieties Agria, Desiree and Hermes were preferred for their mineral contents and
are positively correlated (R= 0.898) with their ash contents. In general; functional
attributes were found maximum in Desi followed by Desiree. A promising
correlation was reported amongst most of these parameters with distinctive
correlation (R=0.953) identified between total phenolic contents and radical
scavenging activity. Post processing parameters like moisture contents, fat
absorption, and sensory evaluation in Lady Rosetta showed its preference over all
other varieties followed by Hermes.
The 2nd phase of the study was divided into four different experiments in
order to identify best packaging material for storage and transit, suitable light
source for retail display, appropriate storage temperature and suitable anti
sprouting agent. Application of suitable packaging systems extends the storage life
by slowing down the respiration rate, protecting them during transit, and conferring
value addition during marketing. As 1st experiment of second phase of study the
efficiency of different packaging materials like jute, nylon, polypropylene, cotton,
low density polyethylene, medium density polyethylene and high density
polyethylene were studied along with control on the premium potato variety “Lady
Rosetta” (selected in the first phase). After harvest potato tubers were washed,
sorted, graded, cured and than placed in different packaging materials at ambient
storage maintained at 25± 2oC. The transition in quality attributes of potato tubers
307
under different packaging materials were studied on the basis of their physico-
chemical, functional and processing parameters. In general weight loss, total
soluble solids, glucose, total sugars, glycoalkaloids, polyphenol oxidase,
peroxidase, chip moisture contents, chip fat absorption increased with the
progression in storage period. Parameters like pH, specific gravity, starch, ascorbic
acids, chip color, chip crispiness and chip flavor decreased with the increase in
storage. Total phenolic contents and radical scavenging activity showed initial
increase followed by decline during increasing storage period. Amongst different
packaging employed potato stored in polypropylene and low density polyethylene
packaging presented best over all retention of vital quality attributes during 63
days storage however, tensile strength of polypropylene packaging made it
advantageous for prolonged potato storage with easy transit operations during
marketing.
Retail display of potato tubers are carried out in super markets under
additional light sources to impart aesthetic value and consumer’s attention however
is associated with potato greening. The objective of second experiment of 2nd phase
was to identify most appropriate light source for best potato variety “Lady Rosetta”
with appreciable retention of different quality parameters. Potato tubers were
placed for 27 days at ambient storage (25± 2oC) under different light sources i.e.
blue, fluorescent, green, mercury and red along with dark storage which also
served as normal control. The results showed maximum retention of different
quality attributes in dark potato storage. Amongst different light sources mercury
and green light retained appreciable retention of different quality parameters with
non significant difference estimated between them nevertheless green light
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established its primacy due to superior processing performance and lower sugar
accumulation. Storage of potato under fluorescent, red and blue light proved to be
precarious due to skin discoloration, increased enzymatic activity and poor
processing performance. Over all results revealed tuber sensitivity to different
colored light along with the assessment of their storage stability.
Potatoes are usually stored under low temperature for sprout prevention and
to ensure their continuous supply when ever needed. Low temperature sweetening
is the principal temperature related disorder being faced by the growers in potato
during storage and is associated with critical storage temperature. The present
study aimed at identifying the appropriate storage temperature for the selected
potato variety with special reference to their quality attributes. Potato variety
“Lady Rosetta” was stored under different temperature regimes i.e. 5oC, 15oC and
25oC to identify most suitable storage temperature. Our results showed significant
variation in different quality attributes in response to different temperature studied.
Storage at 5oC maintained tuber dormancy for 126 days however associated with
increased sugar accumulation and rapid starch depletion during storage
consequently presented poor post processing performance. In contrast storage of
Potato tubers at 15oC retained lower sugar contents and superior processing
performance till the end of storage yet presented increased polyphenol oxidase and
peroxidase activities as compare to those stored at 5oC during the same storage
period. The storage stability of potato tubers at 25oC was significantly tested due to
dormancy break on 84rth day. Our results showed that potato variety “Lady
Rosetta” is cold sensitive and required critical storage temperature for premium
post processing performance.
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Sprouting leads to increased fresh weight loss, elevated sugar contents,
high starch depletion and obstructs air movement under storage atmosphere. The
response of potato variety “Lady Rosetta” was evaluated against the application of
different anti sprouting agents in the fourth experiment of 2nd phase. Dormancy
break in potato tubers was considered complete at sprouting percentage of 25%
with sprout length of >3mm. The single application of different anti sprouting
agents like hot water treatment, spearmint oil, clove oil, and CIPC was carried out
to assess their effectiveness against tuber stability under storage. The tubers were
placed at ambient storage (25oC ±2oC) for 81 days to evaluate changes in physico-
chemical, functional, enzymatic and processing attributes of selected variety.
Results revealed significant response of variety “Lady Rosetta” to all anti sprouting
agents as compare to control. Highest retention of different quality attributes in
potato tubers were identified in CIPC application however mostly found
statistically similar to those estimated in clove oil application. Potato with clove oil
application retained appreciable total phenolic contents and exhibited higher anti
oxidant activity during storage period. Application of spear mint oil and hot water
treatment also proved to be useful in preventing potato sprouting as compare to
control however associated with increased weight loss at the end of storage period.
Post processing sensorial attributes showed the efficacy of all anti sprouting agents
with non significant difference estimated between most of them during storage.
Results showed that triumphant replacement of CIPC with essential oil might be
useful to avert related food safety and environmental issues and ensure organic
potato storage.
310
Integrated post harvest treatments were applied on potato variety “Lady
Rosetta” in the 3rd and last phase of the present study to asses the transition in their
quality attributes along with eventual storage life. Potato variety after preliminary
post harvest operations like sorting, grading, washing and curing treated with hot
water at 55±2oC for 15 minutes. After drying based on the results obtained in
experiment 1 and 2 of the present study potatoes were treated with clove oil (1%)
as anti sprouting agent, packed in polypropylene bags and than stored under dark at
10±1oC for subsequent quality attributes analysis. The results showed remarkable
storage performance of treated potato as compare to those placed under control.
The tubers maintained low weight loss, intact starch contents, low sugar and
glycoalkloids accumulation, during most of the storage period. Integrated treatment
retained appreciable functional potential with low enzymatic activity. Conclusively
tuber maintained their dormancy period for 180 days as compare to control tubers
sprouted on 80th day. In addition monthly pre processing application of different
concentrations of Aloe vera (10%, 20% and 30%) was carried out on potato chips
from integrated treatment to evaluate their processing performance. Though all the
potatoes produced quality product due to their effective post harvest storage
however hydro colloidal (Aloe vera) applications as coating material were found
effective in reducing oil uptake during processing. Steady increase in fat uptake
however observed with in the storage intervals along the storage period. Over all
Aloe vera 20% presented best results with reduced fat absorption and appreciable
chip sensorial attributes.
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RECOMMENDATIONS
“Lady Rosetta” should be used as premium processing variety for potato
industry owing to its suitable size and sphericity, low sprout (%), high dry matter,
and reducing sugars, with over all remarkable processing performance.
Outstanding functional potential and other quality attributes identified in
the “Desi” variety should be the point of interest for potato breeders to develop
indigenous potato variety with considerable functional and processing quality
parameters.
Low Density polyethylene or polypropylene bags should be employed in
place of obsolete jute packaging to prevent post harvest losses during storage.
Retail display of potatoes in super markets should be carried out under
mercury and green lights for the prevention of alkaloidal toxicity and undesirable
greening.
Hot water treatment followed by Clove oil application should be used as an
alternate anti sprouting treatment in place of synthetic CIPC application to ensure
organic potato storage.
Pre processing application of Aloe vera gel at 20% proved to be efficient
technique to reduce fat absorption and toxic acrylamide formation along with
appreciable sensorial scores
Integrated post harvest management of potato variety “Lady Rosetta” on the
basis of best results identified ensured tuber dormancy and prolonged storage life up to
180 days in contrast to 100% observed sprouting in control on the 80th day of storage
311
312
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