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IMPROVING THE SHELF LIFE OF READY TO COOK IDLI

BATTER

6.1 INTRODUCTION

Ready to cook idli batter which was optimized to give desired quality parameters in the

earlier chapters (3 and 4) could only be successfully commercialized as a viable product

only its shelf-life is increased substantially from approximately one day to at least several

days.Idli, unlike other ready to cook food products rapidly gets over fermented as it is a

live actively growing bacterial medium, although common spoilage problems are less.

This is a challenge in terms of its preservation and shelf life. Ready to cook idli batter is

already available in the market as a packaged product. For several years prepared by local

vendors as a perishable product sold on daily basis or stored and sold under refrigerated

conditions. For the first time we have hypothesized that modification of gaseous

environment in the packaged form could regulate the fermentation flora in the medium

leading to longer shelf life. Second part of the hypothesis is that regulating the gaseous

exchange with the external environment could support the modified atmosphere in the

packaged product to work long.

MAP helps to preserve foods by reducing microbial spoilage thereby increasing

storability. MAP is done to maintain the freshness of the produce when purchased.

Success of MAP packaged foods depends on the quality of raw material and hygienic

practices followed during preparation and packaging, the gas mixture used for packaging

and the packaging material. The gases used in MAP are CO2, O2 and N2. Researchers

have successfully applied MAP to perishable foods like fruits, vegetables, flesh foods and

certain dairy products.

6.2 MATERIALS AND METHODS

6.2.1 Materials

1. Modified Atmosphere Packaging machine (VAC Star-Swiss)

2. Head space analyzer (Dansensor, Italy)

3. Gas mixer (Dansensor, Italy)

4. Packaging materials- LDPE, PP, HM

99

6.2.2 Methods

6.2.2.1 Preparation of batter

The selected IR20 idli rice and ADT3 variety black gram dhal were taken in the

optimized ratio of 3:1.18. The quantity required varied for each set of experiment.

Ingredients were soaked and ground and were immediately packaged in the packaging

materials Fig.6.1 shows the research design of this chapter.

6.2.2.2 Selection of packaging materials

Three packaging materials namely low density poly ethylene (LDPE), Poly propylene

(PP), High Molecular (HM) were used for packing the idli batter. The thickness of the

packaging materials is given in Table 6.1. Dimension of the packaging material was 6×10

inches. 100g of the batter was filled in each pack.

Table 6.1

Thickness of packaging materials

Packaging materials Thickness (mm)

LDPE 0.009

LDPE 0.012

LDPE 0.014

PP 0.003

PP 0.005

HM 0.002

HM 0.006

6.2.2.3 MAP of idli batter

MAP was done using Modified Atmosphere Packaging machine (VAC Star-Swiss). MAP

machine consists of three gas cylinders viz., oxygen, carbon dioxide and nitrogen, each of

which is connected to a gas mixer provided with a separate cylinder where the required

combination of gases can be set and stored temporarily in buffer tank. Gas analyzer is

another important component of the MAP machine which helps to check if the gas is

mixed in the expected combination and the same is used for determining gas in the head

100

space of the packaged sample as and when required. Plate 6.1 shows the MAP machine.

The batter in each packet was packaged with modified air of required combination.

6.2.3 Respiration dynamics of the idli batter

Respiration dynamics was carried out to find the percentage of oxygen utilized and

percentage of carbon dioxide released during fermentation of batter. Respirometer as

designed by Bosco (1997) was used. Plate 6.2 shows the picture of respiration dynamics

done for the idli batter using respirometer connected to gas analyzer. The respirometer

consists of a glass jar without spout of capacity 250 mL resting on a flat MS plate and

covered with another MS plate. Both the plates had hole at each corner through which

bolt were inserted. By tightening the nuts of these bolts, the glass jar could be closed with

the cover plate. The joint between the glass jar and the cover plate was made air tight by

providing a neoprene rubber gasket. The cover plate had one hole at the centre where the

gas septum had been fixed for sampling the gas. Gas tightness of Respirometer was

verified by the respirometer ability to hold 50 mm vacuum for 15 minutes as done by

Plate 6.1 Modified Atmosphere Packaging (MAP) machine

101

Brown (1922). For the experiment, 100g of fresh ground batter was taken in 250 ml

beaker. Atmospheric air was maintained inside the beaker. The Respirometer was

connected to the gas analyzer to monitor the change in gas environment every half an

hour. The experiment was conducted for 12.02h (optimized fermentation time).

Plate 6.2 Respirometer connected to gas analyzer

102

6.2.4 EXPERIMENT I

Experiment I was carried out to find suitable packaging material for idli batter. The study

was designed for 3 days (Sridevi et al., 2010), hence a total of 126 packets (7 packaging

materials × 6 gas treatments × 3 days) were required. Based on the optimized ratio, batter

was prepared. In each packaging material 100g of batter was packaged with gas treatment

of 0% CO2, 5% CO2, 10% CO2, 15% CO2 and vacuum packaging and sealed. The

package in which no treatment was done served as the control. The packaged batters were

stored in room temperature (30 C). Each day 42 packets representing 7 packaging

material and 5 gas treatments were analyzed for the gas mixture using gas analyzer.

6.2.5 EXPERIMENT II

In experiment II, the idli batter was packaged and sealed with 12 gas treatments and three

controls were used. Batter placed in vessel served as control I, batter packaged and sealed

with ordinary sealing machine served as control II, the batter packaged in packaging

material but not sealed served as control III. The gas treatments are shown in Table 6.2.

The study was done using selected 3 packaging material. Hence a total of 215 samples

were required. The MA packaged batter and control packs were stored in room

temperature (30 C). Each day 43 samples stored in three different packaging materials

with 12 gas treatments including 3 controls were analyzed for the gas concentrations (%)

followed by sensory analysis of the idli cooked from packaged batter. Overall quality

based on the colour, texture, fermented aroma of the idli was assessed.

103

Table 6.2

Gas treatment used in experiment II

Treatments CO2 (%) O2 (%) N2 (%)

1 00 15.0 85.0

2 05 15.0 80.0

3 10 15.0 75.0

4 15 15.0 70.0

5 00 17.5 82.5

6 05 17.5 77.5

7 10 17.5 72.5

8 15 17.5 67.5

9 00 20.0 80.0

10 05 20.0 75.0

11 10 20.0 70.0

12 15 20.0 65.0

13 Control I Batter in vessel

14 Control II Batter in unsealed package

15 Control III Batter packaged with ambient air

6.2.6 EXPERIMENT III

In experiment III, selected one packaging material and 8 gas treatments and control were

used. Gas treatments are shown in Table 6.3. In this experiment the batter packages were

left to check the extended shelf life of the batter.

Table 6.3

Gas treatment used in experiment III

Treatments CO2 (%) O2 (%) N2 (%)

1 0 15.0 85.0

2 0 12.5 87.5

3 0 10.0 90.0

4 0 07.5 92.5

5 5 15.0 80.0

6 5 12.5 82.5

7 5 10.0 85.0

8 5 07.5 87.5

104

6.3 RESULTS AND DISCUSSION

6.3.1 Respiration dynamics

Respiration is usually the measure oxygen uptake or the production of CO2, producing

heat and water vapour. The results of respiration dynamics give an idea to flush the

package with required atmosphere so that steady state conditions are reached

immediately (Zagory and Kader, 1988). The O2 consumption and CO2 evolution differ

based on the composition such as fatty acids, sugars or organic acids of the respiring

sample (Dilley et al, 1990 and Platenius, 1942).

Fig.6.1 Change in gas concentration during its fermentation time

Fig.6.1 showed the O2% consumed and CO2 % evolved during the fermentation of idli

batter. As fermentation began, the O2% declined from 21% to 13.9%. The increase in

CO2% began after 2 h and gradually increased from 0% to 12.9%. The results showed

that 100g of idli batter consumed 7.1% O2 and produced 12.9% of carbon dioxide. Based

on the results of respiration dynamics MAP of ready to cook idli batter was done with

different gas treatments and the results are discussed below.

105

6.3.2 EXPERIMENT I

Table 6.4 shows the changes in atmosphere of the packaged idli batter. In treatment1

where the package was packed with lack of oxygen and carbon dioxide (0% O2 and 0%

CO2) showed a gradual increase in CO2 over three days of storage. This increase in CO2

is a result of fermentation of idli batter inside the package. The O2 (%) remained zero in

the LDPE packages but HM and PP showed increase in O2, which meant that the

packaging material permitted permeability of air. Fig.6.2 shows the changes in gas

mixture among different packaging material over three days of storage.

In treatment 2 where the package was flushed with 5% CO2, it was found that there was

increase in CO2 % from 5% to a maximum of 14.4 % CO2 in LDPE packaging material

during the second day of storage. In the packaging material PP (0.003mm) there was

decrease in CO2 to 0.8% on the third day. The O2 concentration in PP (0.003mm) and

HM (0.002 mm) were not maintained inside the package. Fig.6.3 shows the changes in

gas mixture among different packaging material over three days of storage.

In treatment 3 where the 10% CO2 was flushed in the package, LDPE of higher thickness

showed fermentation effect on the batter with increase in CO2, whereas in LDPE of lower

thickness, PP and HM the change in gas system was not gradual.

In treatment 4, the package was flushed with 15% CO2, increased in LDPE of medium

and lower thickness and the concentration of CO2 varied in other packaging materials

over the storage period. Fig.6.4 shows the changes in gas mixture among different

packaging materials.

Treatment 5 was vacuum packaging and over the storage period the gas concentrations

were not analyzed as the pressure was too low to detect the gas in the head space.

Treatment 6 was control with lack of gas treatments but package had ambient gas

composition. The atmospheric air in package favoured fermentation of batter which led to

decrease in O2 concentration.

From the results of experiment I it was inferred that gas permeability differed with

different packaging material. The O2 permeability was less than that of CO2 in LDPE of

varying thickness helped to maintain the atmosphere within the package compared to

other packaging materials. This result is supported by the study done by Bosco (1997),

106

who reported that, the O2 permeability of LDPE and PP was less than that of CO2 and the

variation in permeability of a film is due to the fact that the film were purchased from

the retail market at different places and might be from different batches of production

Table 6.4

Change in gas mixture over storage period

Packaging

material

Day 1 Day 2 Day 3

CO2 (%) O2 (%) CO2 (%) O2 (%) CO2 (%) O2 (%)

LDPE (0.14 mm)

Treatment 1 0.114 0 11 0 11.1 0.017

Treatment 2 5.6 0.009 6.3 1.07 10.9 0.009

Treatment 3 10.5 0.1 13.8 0 15.5 0

Treatment 4 14.2 0.008 12.4 0 8.9 19.4

Treatment 5 - - - - - -

Treatment 6 0 21 2.1 14.8 4.2 7.15

LDPE (0.12 mm)

Treatment 1 0.114 0 10.3 0 10 0.265

Treatment 2 5.6 0.009 10.6 5.4 10.8 5.2

Treatment 3 10.5 0.1 12.6 0 15.4 0.09

Treatment 4 14.2 0.008 14.9 0.011 14.9 0

Treatment 5 - - - - - -

Treatment 6 0 21 4.1 7.56 3.1 12.6

LDPE (0.009 mm)

Treatment 1 0.114 0 10.3 0 12.8 0

Treatment 2 5.6 0.009 14.4 0.484 15 1.2

Treatment 3 10.5 0.1 12.9 0 5.2 0.036

Treatment 4 14.2 0.008 10.5 0.095 12.6 0.015

Treatment 5 - - - - - -

Treatment 6 0 21 3.3 8.91 0.3 19.8

PP (Thin)

Treatment 1 0.114 0 9.9 0.112 12.7 0.112

Treatment 2 5.6 0.009 13.5 19.5 0.8 19.5

Treatment 3 10.5 0.1 11.3 19.1 1.2 19.1

Treatment 4 14.2 0.008 13.4 0.908 15.2 0.908

Treatment 5 - - - - - -

Treatment 6 0 21 0 20.3 0.3 19.8

107

PP (Thick)

Treatment 1 0.114 0 5.1 0.549 10.2 0.539

Treatment 2 5.6 0.009 10.8 0.001 15 0.001

Treatment 3 10.5 0.1 14.3 0.032 15 0

Treatment 4 14.2 0.008 15.2 0.001 14.6 0.149

Treatment 5 - - - - - -

Treatment 6 0 21 8.2 6.2 0 0.3

HM (Thin)

Treatment 1 0.114 0 3.4 3.18 11.6 9.5

Treatment 2 5.6 0.009 2.8 0.04 5.9 19.2

Treatment 3 10.5 0.1 0 20.4 0.8 18.9

Treatment 4 14.2 0.008 0.7 19.6 1 19.3

Treatment 5 - - - - - -

Treatment 6 0 21 0.4 19.5 0 20.3

HM (Thick)

Treatment 1 0.114 0 3.4 4 19.7 9.7

Treatment 2 5.6 0.009 6 0.5 7.3 0.6

Treatment 3 10.5 0.1 0.5 19.3 2.8 17.1

Treatment 4 14.2 0.008 0.1 20.3 4.1 9.39

Treatment 5 - - - - - -

Treatment 6 0 21 0.3 19.7 0.1 20.2

At low oxygen levels, anaerobic respiration can occur, resulting in production of

substances that contribute to off-flavours and odours (Lee et al, 1995 and Zagory 1995).

Hence the idli prepared from the batter were subjected to sensory analysis only for its

texture. Idli made from the batter packaged in different packaging material scored very

low rating which might be due to deterioration of the batter. The experiment was

repeated with combination of both O2 and CO2 in LDPE of varying thickness.

108

Fig. 6.2.a Treatment 1 (0% CO2) showing change in CO2 level (%) among different

packaging material

Fig. 6.2.b Treatment 1 (0% CO2) showing change in O2 level (%) among different

packaging material

109


packaging material


packaging material

110


packaging material


packaging material

111

6.3.3 Experiment II

Table 6.5 to 6.8 shows the changes in gas concentrations in the packaging materials with

idli batter. The 12 treatments showed the rate of fermentation of batter in different MAP

system in different packaging material at room temperature (30 C). Treatment 1 to 12

showed increase in concentration of CO2% within 48h of packaging which is due to the

evolution of CO2 during fermentation of the batter.

Treatment 1 showed gradual increase in fermentation rate of the batter for five days of

storage period compared to other treatments. The percentage of O2 decreased gradually

from 15% to 1.75% (LDPE 0.12mm). Fig.6.5 showed the changes in concentration of

CO2 and O2 among LDPE of varying thickness. The batter in treatments 5 to 12 which

were flushed with 17.5% to 20% O2 led to complete consumption of O2 in LDPE of 0.014

and 0.012mm by the batter supporting fermentation and also whey separation. During

storage of batter whey separation persisted (Nisha et al, 2005). The reason stated by

Nisha et al was that idli batter is foam in which gas molecules are entrapped in a solid-

liquid phase. The batter collapse and whey separates when the high energy interface takes

place during air-water interface. Fig.6.5 to 6.14 shows the depletion of O2 curve. LDPE

of 0.009mm did not support the MAP system showing variations in gas concentration

over the period of batter storage.

The gas combination was not analyzed for control I and II as they were exposed to the

atmospheric air. The O2 (%) concentration in control III was zero per cent and that of

CO2 decreased from 11% (2nd

day) to 5.7 % (5th

day) during storage. It showed that the

oxygen was consumed for the fermentation process and the carbon dioxide evolved was

decreased due to its permeability through the packaging material.

112

Table 6.5

Concentration of gases in LDPE (0.014mm) during the storage period

Treat-

ments

Gas combinations

Day 0 Day 1 Day 2 Day 3 Day 4 Day 5

CO2 (%) O2 (%) CO2 (%) O2 (%) CO2 (%) O2 (%) CO2 (%) O2 (%) CO2 (%) O2 (%) CO2 (%) O2 (%)

1 00 15.0 08.1 9.40 10.4 02.2 00 0.00 6.2 1.500 6.2 0.000

2 05 15.0 07.0 7.31 03.3 13.6 6.8 0.44 5.9 0.453 6.2 7.000

3 10 15.0 05.4 11.2 02.6 14.7 1.2 18.8 8.3 2.740 6.0 3.100

4 15 15.0 02.5 16.7 05.4 0.707 4.4 4.09 4.7 0.424 5.5 0.600

5 00 17.5 04.3 6.38 08.0 0.087 6.9 0.94 4.3 2.660 9.6 0.850

6 05 17.5 09.6 0.72 04.0 04.59 00 0.00 5.9 0.085 6.4 0.002

7 10 17.5 12.2 0.23 13.7 0.077 6.1 0.40 6.6 0.000 6.1 0.800

8 15 17.5 10.1 1.26 05.3 0.730 6.1 0.19 4.6 0.172 5.7 0.70

9 00 20.0 22.1 0.001 08.1 0.024 6.3 0.16 5.4 0.076 5.8 0.137

10 05 20.0 16.7 0.12 08.1 0.045 4.9 0.09 4.9 0.134 5.0 0.142

11 10 20.0 16.5 4.11 10.3 0.205 8.5 1.13 2.8 9.460 7.1 0.873

12 15 20.0 14.9 3.03 07.1 02.06 7.5 0.14 6.0 0.361 5.8 0.197

113

Table 6.6


Treat-

ments

Gas combinations



1 00 15.0 07.2 07.05 09.3 3.524 10.1 2.650 11.7 1.95 11.9 01.75

2 05 15.0 07.6 04.72 03.0 9.780 05.4 0.601 05.7 0.71 04.0 00.29

3 10 15.0 11.0 07.85 09.6 0.759 08.2 0.534 08.2 3.16 05.5 00.09

4 15 15.0 05.7 12.40 05.5 0.486 04.8 0.291 03.9 0.26 00.0 00.00

5 00 17.5 12.4 00.54 08.3 0.206 00.4 20.10 08.4 0.113 05.8 11.10

6 05 17.5 15.4 02.10 08.7 1.450 08.1 0.622 07.2 0.044 00.2 20.80

7 10 17.5 06.9 03.79 06.2 0.246 08.8 8.470 05.4 0.197 04.9 00.22

8 15 17.5 16.2 0.268 08.8 0.071 07.2 0.453 04.9 0.194 09.2 01.42

9 00 20.0 19.3 0.161 05.7 0.164 05.8 0.017 05.4 0.367 05.8 00.03

10 05 20.0 05.3 14.50 15.7 0.000 07.0 0.000 05.1 0.161 07.2 00.36

11 10 20.0 05.0 13.60 08.0 5.150 04.3 0.238 07.5 0.252 06.6 00.37

12 15 20.0 15.2 03.14 06.6 8.910 09.3 0.152 04.9 0.185 09.1 00.24

114

Table 6.7


Treat-

ments

Gas combinations



1 00 15.0 10.2 09.45 09.0 0.08 1.7 18.1 7.2 08.69 05.6 00.16

2 05 15.0 01.1 18.90 08.9 2.54 4.9 0.12 8.9 00.79 09.3 00.12

3 10 15.0 08.3 05.49 04.0 1.87 6.0 6.61 4.8 00.34 07.7 00.09

4 15 15.0 16.5 00.43 05.4 9.69 0.2 20.5 9.3 03.35 04.6 014.3

5 00 17.5 17.3 00.24 09.3 0.16 1.0 20.2 5.4 00.20 06.6 00.29

6 05 17.5 18.7 00.31 06.2 0.42 7.8 1.21 2.4 18.40 08.5 01.79

7 10 17.5 07.8 05.29 04.5 1.96 8.9 1.03 5.4 11.90 06.1 06.20

8 15 17.5 13.5 00.69 08.9 0.06 5.3 11.3 14 01.61 10.0 00.39

9 00 20.0 10.9 01.26 11.3 0.91 4.6 0.19 10.8 00.04 05.7 00.09

10 05 20.0 11.2 06.71 12.5 1.22 5.9 0.17 7.3 00.52 10.5 01.65

11 10 20.0 17.9 00.12 09.5 0.29 10.4 0.65 8.0 00.04 04.4 13.20

12 15 20.0 10.0 00.27 05.4 0.77 3.8 2.37 11.2 02.19 07.7 00.09

115

Fig 6.5.a Treatment 1 (0% CO2 and 15% O2) showing percentage of CO2 (%)

Fig.6.5. b Treatment 1 (0% CO2 and 15% O2) showing percentage of O2 (%)

Storage period

Storage period

116

Fig 6.6.a Treatment 2 (5% CO2 and 15% O2) showing percentage of CO2 (%)

Fig 6.6.b Treatment 2 (5% CO2 and 15% O2) showing percentage of O2 (%)

Storage period

Storage period

117

Fig. 6.7.a Treatment 3 (10% CO2 and 15% O2) showing percentage of CO2 (%)

Fig. 6.7.b Treatment 3 (10% CO2 and 15% O2) showing percentage of O2 (%)

Storage period

Storage period

118



Storage period

Storage period

119

Fig. 6.9.a Treatment 5 (0% CO2 and 17.5% O2) showing percentage of C O2 (%)

Fig. 6.9.b Treatment 5 (0% CO2 and 17.5% O2) showing percentage of O2 (%)

Storage period

Storage period

120

Fig. 6.10.a Treatment 8 (15% CO2 and 17.5% O2) showing percentage of CO2 (%)

Fig. 6.10.b Treatment 8 (15% CO2 and 17.5% O2) showing percentage of O2 (%)

Storage period

Storage period

121



Storage period

Storage period

122



Storage period

Storage period

123



Storage period

Storage period

124



Storage period

Storage period

125

Table 6.8

Sensory scores of the product made from batter packaged in LDPE

(0.014mm)

Treatments Sensory scores

Day 1 Day 2 Day 3 Day 4 Day 5 1 8.1 9.1 7.1 1 1

2 7.5 8.5 5.1 5.1 5.2

3 5.2 8.5 1 1 1

4 9.3 8.3 1 1 5.4

5 8.5 7.3 7.2 7.7 1

6 8.5 7.7 6.2 7.0 1

7 8.1 5.7 1 1 1

8 6.4 7.2 1 1 1

9 8.8 7.7 6.1 1 1

10 8.3 8.2 7.3 7.1 3.5

11 8.1 8.0 4.3 1 3.7

12 8.0 8.0 7.3 1 3.0

Control I 6.7 - - - -

Control II 8.0 5.2 - - -

Control III 8.2 7.4 - - -

Table 6.9

Sensory scores of the product made from batter packaged in LDPE

(0.012mm)


Day 1 Day 2 Day 3 Day 4 Day 5 1 3.0 7.3 8.2 8.3 9.0

2 4.0 7.1 5.4 5.6 5.0

3 6.2 7.4 7.9 6.9 6.2

4 6.3 7.2 6.4 6.8 5.1

5 6.1 6.5 5.2 6.8 5.7

6 6.3 8.3 8.9 8.5 7.3

7 8.2 8.5 6.8 6.4 5.1

8 6.3 7.2 7.7 5.9 6.3

9 8.2 6.3 6.4 5.2 6.2

10 8.5 7.3 5.9 6.0 6.1

11 8.5 4.2 5.4 6.7 6.6

12 8.2 6.0 4.0 5.2 5.3

Control I 6.8 - - - -

Control II 7.4 4.7 - - -


Table 6.10

126

Sensory scores of the product made from batter packaged in LDPE (0.009mm)


Day 1 Day 2 Day 3 Day 4 Day 5 1 7.5 6.4 1.5 1.6 3.8

2 8.1 5.3 1.5 1.8 3.7

3 5.4 5.9 1.7 1.9 2.7

4 8.2 4.5 1.3 1.4 4.3

5 8.0 6.1 1.4 1.7 2.7

6 8.3 6.2 4.0 1.6 1.6

7 8.5 6.3 6.2 1.5 2.7

8 8.2 8.1 1.7 1.8 1.8

9 5.3 8.3 6.5 5.2 3.2

10 7.8 7.4 5.7 4.3 2.9

11 5.2 8.1 5.3 2.5 3.2

12 5.0 6.3 5.2 2.0 1.6

Control I 6.8 - - - -

Control II 7.3 5.0 - - -


Table 6.8 to 6.10 showed the sensory scores of idli made from batter treated with

different gas combinations in different packaging material. The sensory score represented

the overall quality of the idli. Sensory scores of idli prepared on the second day of storage

showed high acceptability which might be due to the reason that the batter had been

fermented and gave idli of high acceptability. The scores ranged from 4.2 to 9.1

(treatment 11 in LDPE -0.012 mm and treatment 1 in LDPE- 0.014 mm). The sensory

scores on the third, fourth and fifth day showed poor acceptability of the product except

for treatments in LDPE 0.012 which increased during the storage period. The highest

score obtained was 9 for treatment 1 (Fig.6.15) followed by 7.3 for treatment 6 (Fig.6.16)

on the fifth day of storage.

The batter in control I was discarded due to over fermentation after 24 h followed by

fungal contamination. The batter in control samples were evaluated for sensory for a

maximum two days whereas the batter in packages was used for idli preparation and

evaluated for sensory on all storage days in spite of its poor scores. Thou there was whey

separation which made idli harder, the packaged batter used for idli preparation when

compared to control.

127

The results of experiment II discussed from gas concentration in different treatments and

different packaging material showed that LDPE of medium thickness (0.012 mm) may

support to maintain the MAP system inside the packaged atmosphere when compared to

LDPE of other thickness . The gas treatment of 0% CO2 with 15% O2 and 5% CO2 with

15% O2 were found to extend the shelf-life of the batter compared to other gas treated

samples and control samples.

Fig. 6.15 Comparison of sensory scores of idli made from

treatment 1 (0% CO2 and 15% O2)

128

Fig. 6.16 Comparison of sensory scores of idli made from

treatment 6 (5% CO2 and 15% O2)

6.3.4 Experiment III

The observations of experiment III are shown in Table 6.11. It was found that the

percentage of carbon dioxide increased in all treatments except for 8 which showed very

low CO2% and low O2%. The consumption of O2 percentage was high showing complete

decrease of O2 percentage in the package. During fermentation of batter oxygen is

consumed and when the fall is below 1% may lead to anaerobic respiration (Lee et al,

1995 and Zagory 1995). In the table 6.11, on the seventh day of storage, all treatments

showed poor concentrations of O2% except treatment 1 which showed 1.4% O2. Initial

pH of the fresh batter 6.41 and change in pH of the batter in different treatments over

seven days of storage showed decrease in pH. The change in pH is associated with the

development of Streptococcus faecalis producing both lactic acid, which lowers the pH

and carbon dioxide which leavens the batter (Balasubramanian and Viswanathan, 2007a).

The control sample was discarded on the third day due to fungal contamination.

129

Table 6.11

Comparison of gas mixture on the first day and seventh day of storage

Treatments Day 0 Day 7 CO2 (%) O2 (%) pH CO2 (%) O2 (%) pH

1 0 15.0 6.41 11.3 1.4 4.32

2 0 12.5 6.41 12.6 0.4 4.10

3 0 10.0 6.41 10.3 0.7 4.31

4 0 07.5 6.41 12.4 0.9 4.31

5 5 15.0 6.41 12.9 0.0 4.28

6 5 12.5 6.41 14.6 0.5 4.00

7 5 10.0 6.41 13.1 0.6 4.10

8 5 07.5 6.41 3.4 0.0 4.22

Control Ambient atmosphere 6.41 - - -

Table 6.12

TPA parameters of idli made from MAP batter

Treatments Hardness (N) Adhesiveness (N s) Springiness Cohesiveness Chewiness Resilience

1 17.020±4.68 -07.257±5.58 0.874±0.07 0.671±0.02 1024.01±333.8 0.386±0.02

2 21.455±1.22 -09.924±5.52 0.814±0.05 0.622±0.04 1106.65±95.3 0.337±0.04

3 21.705±2.72 -09.907±3.39 0.829±0.02 0.645±0.00 1181.11±116.7 0.364±0.02

4 19.500±2.63 -15.461±13.27 0.852±0.11 0.663±0.09 1112.96±155.5S 0.369±0.06

5 27.315±2.55 -10.757±05.48 0.870±0.01 0.686±0.07 1045.67±35.7 0.383±0.03

6 28.955±0.45 -12.552±02.95 0.843±0.04 0.624±0.05 1229.40±131.8 0.356±0.05

7 28.571±0.21 -09.417±06.58 0.858±0.05 0.666±0.03 1339.51±34.7 0.377±0.03

8 27.152±0.52 -14.790±00.09 0.904±0.06 0.720±0.00 1761.41±9.2 0.336±0.01

Control - - - - - -

The texture of idli prepared from the treated batter was analyzed and Table 6.12 shows

the TPA values of the idli. The hardness of the idli ranged between a minimum of 17.02

N (treatment 1) to a maximum hardness of 28.95 N (treatment 6). The hardness of idli

was low for the treatments 1 to 4 when compared to other treatments which were due to

the whey separation seen in treatment 5 to 8. The maximum springiness was found for the

idli made from the treatment 8 followed by idli made from treatment 1 and 5.

130

Cohesiveness was maximum for the idli made from the treatment 8 followed by 2 and 6.

Resilience was maximum for the idli made of treatment 1 (0.386) followed by treatment

7 (0.377). The texture profile values when compared with the optimized value show that

idli made from treatments 1 to 4 were soft compared to idli made from other treatments.

Table 6.13

Overall quality of idli

Treatments CO2 (%) O2 (%)

Overall quality

1

0

15

8.6 ± 0.84

2

0

12.5

7.0 ± 0.00

3

0

10

7.0 ± 1.34

4

0

7.5

7.4 ± 2.4

5

5

15

5.8 ± 0.49

6

5

12.5

6.4 ± 0.49

7

5

10

6.6 ± 0.70

8

5

7.5

4.0 ± 5.65

Control

Batter packaged with

ambient air

-

Table 6.13 shows the scores of overall quality of the idli made from MAP treated batter.

The maximum score was 8.6 (Treatment 1) followed by 7.4 (Treatment 4). The overall

comparison of the sensory scores show that treatments 1 (8.6), 2 (7.0) and 4 (7.4) had

high scores respectively when compared to treatments 5 to 8. Studies done by Day

(1996) and Zagory and Kader, (1988) showed that by modifying the atmospheric oxygen

level, particularly by lowering the oxygen concentration inside the package, the

respiration rate of the packaged produce is slowed down and the sensory shelf life can be

extended which cannot be applied to the current study. Idli batter being a live product

which produces 12.9% of CO2 during fermentation requires oxygen in order to maintain

aerobic condition and to sustain the aroma of the fermented batter and the final product

when the batter is steamed. Hence the study done by Song et al., (1998) Mattheis and

131

Fellman, (2000) supports the current study who reported that production of aromatic

compounds of many fruit, including apple, banana, pear, peaches, strawberries and

others, can be adversely affected by low O2 and elevated CO2 i.e., synthesis of aroma

compounds are generally suppressed. As mentioned in chapter 4, fermented aroma is one

the criteria of idli which will be considered for sensory analysis and hence the treatment

with high O2% may support the sensory quality of MAP packaged idli. The result of table

6.13 show that idli made from batter packaged with 0% to 5% CO2 and O2 ranging from

7.5% to 15% gave better results compared to all other treatments applied in the above

experiments.

6.4 CONCLUSION

From this study it can be concluded that ready to cook idli batter packaged in medium

thickness (0.012 mm) LDPE flushed with 0% CO2 and 7.5 to 15% O2 could increase the

shelf-life up to seven fold increase without compromising the sensory qualities at room

temperature.

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