An innovative technique for extending shelf life of strawberry: Ultrasound

at SciVerse ScienceDirect

LWT - Food Science and Technology 52 (2013) 93e101

Contents lists available

LWT - Food Science and Technology

journal homepage: www.elsevier .com/locate/ lwt

An innovative technique for extending shelf life of strawberry: Ultrasound

Mehmet Seçkin Aday a,*, Riza Temizkan a, Mehmet Burak Büyükcan b, Cengiz Caner a,**aDepartment of Food Engineering, Çanakkale Onsekiz Mart University, Engineering-Architecture Faculty, Terzioglu Kampusu, 017020 Canakkale, TurkeybDepartment of Agricultural Machinery, Çanakkale Onsekiz Mart University, 17020 Canakkale, Turkey

a r t i c l e i n f o

Article history:Received 28 May 2012Received in revised form14 August 2012Accepted 13 September 2012

Keywords:StrawberryUltrasoundFT-NIRShelf lifeTexture

* Corresponding author. Tel.: þ90 2862180018/260** Corresponding author.

E-mail addresses: [email protected] (M.S(C. Caner).

0023-6438/$ e see front matter � 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.lwt.2012.09.013

a b s t r a c t

Ultrasound is one of the newest nonthermal methods to extend shelf life of fresh fruits during storage.The effectiveness of ultrasound depends on wave frequency, power and treatment time. The presentstudy was designed to determine the effect of different ultrasound powers (30 W, 60 W, 90 W) andtreatment times (5 min, 10 min) on quality of strawberry. Oxygen concentration inside packages ofstrawberries which treated with 30 W and 60 W ultrasound powers were higher than 90 W and control(CNT) groups. A sharp increase in CO2 release rate was observed for the CNT and 90 W treatments duringthe storage. Attributes such as pH, total soluble solid content and color for the 30W and 60 W treatmentswere better than CNT and 90 W treatments. Decay incidence analysis confirmed that all ultrasoundtreatments were effective to reduce mold growth. The 30 W and 60 W treatments maintained bettertextural properties compared with 90 W and CNT groups. FT-NIR analysis was used to quantify water andsugar content of strawberries. As a result, it was concluded that ultrasound power as high as 90 Wresulted in detrimental effects on strawberry quality, while power levels between 30 W and 60 W hadimproved quality and can be used to extend shelf life of strawberry.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Strawberry is a delicate fruit with high nutritional quality andexcellent organoleptic properties (Correia et al., 2011). However,this fruit has an extremely short postharvest life due to tendernessand susceptibility to mechanical injury, rapid dehydration, andinfections by several pathogens (Chen, Liu, et al., 2011). Traditionalmethods used for preventing undesirable change of fruit attributesduring storage, have a detrimental effect on nutritional propertiesand perceived quality. Therefore it’s necessary to find alternativemethods to meet consumer expectations such as attractive senso-rial properties and to satisfy public concern about the risks of newtechnologies for human health, environment, and food safety(Dotto, Pombo, Martínez, & Civello, 2011).

One of the newest nonthermal methods to extend shelf life offresh fruits and vegetables is using ultrasound. The ultrasoundtechnology comparing with other novel techniques is perceived tobe safer, non-toxic, environmental friendly and it is assumed asbenign by public due to its use in hospitals for diagnostic imagingpurposes (Feng, Barbosa-Canovas, & Weiss, 2011). The effect of

7; fax: þ90 2862180541.

. Aday), [email protected]

All rights reserved.

ultrasound in food treatment depends onmultiple factors includingfrequency and power of ultrasonic generator, medium temperature,pressure of the treatment, and characteristics of the treatmentliquid (Manas, Pagan, & Raso, 2000).

Numerous studies have attempted to explain the effect ofultrasound on fruits, vegetables, fruit juices and dairy products.Sagong et al. (2011) reported that combined treatment of ultra-sound 30 W/L (40 kHz) and organic acids (malic, lactic and citricacid) were effective at pathogen reductionwithout affecting quality(color and texture) on lettuce during seven days of storage. Yang,Cao, Cai, and Zheng (2011) found that combined salicylic acid(0.05 mM) and ultrasound treatment (40 kHz, 8.8 W/L, 10 min)reduced the Penicillium expansum in peach and did not impair thequality after six days of storage at 20 �C. Zhou, Feng, and Luo (2009)demonstrated that ultrasound (21.2 kHz, 200W/L, 2 min) enhancedthe reduction of Escherichia coli on spinach from 0.7 to 1.1 log CFU/gsample.

Despite considerable amounts of literature have been publishedon ultrasound application, many of themwere dealt with microbialquality rather than physical and chemical properties. Furthermoreno scientific data are available regarding to the use of ultrasoundwith different treatment times and power. Therefore, the aim ofthis paper was to examine the effect of different ultrasound powerand treatment times on physical (color, texture) and chemicalproperties (gas composition inside package, pH, total soluble solid,FT-NIR analysis) of strawberry during four weeks of storage at 4 �C.

Delta:1_given name

Delta:1_surname

Delta:1_given name

Delta:1_surname

mailto:[email protected]

mailto:[email protected]

www.sciencedirect.com/science/journal/00236438

http://www.elsevier.com/locate/lwt

http://dx.doi.org/10.1016/j.lwt.2012.09.013



Storage Time (Weeks)

0 1 2 3 4 5

O2 C

once

ntra

tion

(kPa

)

0123456789

1011121314151617181920212223


0 1 2 3 4 5

CO2 C

once

ntra

tion

(kPa

)

02468

10121416182022242628303234363840

A

B

Fig. 1. Effect of different treatments [ 0 W-5 min (CNT5M), 0 W-10 min(CNT10M), 30W-5 min (30W5M), 30 W-10 min (30W10M), 60 W-5 min(60W5M), 60 W-10 min (60W10M), 90 W-5 min (90W5M), 90 W-10 min (90W10M)] on headspace gas composition during storage A) O2 and B) CO2.Vertical bars denote standard deviation of three replicates.

M.S. Aday et al. / LWT - Food Science and Technology 52 (2013) 93e10194

2. Material and methods

2.1. Materials

Strawberry (Fragaria� ananassa) cv. Camarosa was harvested atcommercially ripe stage by hand from a private farm in Yenice,Canakkale, Turkey. Fruits with signs of visual defect or physicaldamage were discarded. Selected fruits of uniform size and colorwere randomly distributed into 8 groups.

2.2. Treatments

For the ultrasound treatments, three replicates of 500 g straw-berries were immersed in 1000 ml glass beaker which was filledwith distilled water for per treatment. Metallic probe (1.9 cmdiameter of generator) (Vibra Cell505, Newtown, USA) wasimmersed in glass beaker to create acoustic cavitations. Straw-berries were treated with 20 kHz ultrasound at powers of 30 W/L,60 W/L, and 90 W/L for 5 and 10 min. Power intensities werecalculated around 10.6, 21.2 and 31.8 W/cm2 for 30 W/L, 60 W/L,and 90 W/L, respectively. Treatments and abbreviations can besummarized as follows:

1) Control: Strawberries immersed in distilled water for 5 min(CNT5M)

2) Control: Strawberries immersed in distilled water for 10 min(CNT10M)

3) 30Wultrasound treatment: Strawberries treatedwith 30W for5 min (30W5M)






After treatments, strawberries were dried for 5 min, in order toremove excess water. Approximately, 200 g fruits were packaged inpolylactic acid (PLA) trays which were supplied by HuhtamakiIstanbul Ambalaj Sanayi A.S. (Istanbul, Turkey). For each treatment,twenty packages of strawberries were prepared and four packageswere used at each week for the same treatment. Strawberries werepackaged under atmospheric conditions (21 kPa O2/0.03 kPa CO2)for 4 weeks at 4 �C. Transmission rates of package film for O2, CO2and H2O were 620 cm3 mil/m2 day atm, 2800 cm3 mil/m2 day atmand 340 g mil/m2 day, respectively.

2.3. Package gas composition

Gas compositions (O2 and CO2) inside the packages weremonitored with a gas analyzer (OxyBaby, HTK, Hamburg,Germany). The needle of gas analyzer was inserted to each packagethrough an adhesive rubber septum to prevent air leaking from thepackage. After determining the gas composition, packages wereused for further analysis (Aday & Caner, 2010).

2.4. pH measurement

Strawberry was squeezed and the resulting juice was filteredthrough cheesecloth. Then pH of strawberry juice was determined

by using a digital pH meter (Sartorius PP-50, Gottingen, Germany)at room temperature (Caner & Aday, 2009).

2.5. Total soluble solids (TSS)

Strawberry was homogenized and the obtained juice wasfiltered. A drop of the juice was placed on Atago Pal-1 pocketrefractometer (Atago Co. Ltd, Tokyo, Japan) and results expressed as% Brix. Refractometer was calibrated with distilled water beforemeasurements (Caner, Aday, & Demir, 2008).

2.6. Surface color

Strawberry color was measured by using Minolta CR-400(Konica Minolta Sensing, Osaka, Japan). Measurements weretaken on equatorial zone of strawberry. CIELAB color variables (L*-Lightness and a*-rednessegreenness) were presented. Colorimeterwas calibrated against a standard white plate before measurements(Caner & Aday, 2009).

2.7. Texture profile analysis (TPA)

Texture profile analysis was performed to determine firmness,springiness, cohesiveness, adhesiveness, gumminess, resilience andchewiness of strawberry. Samples were analyzed with TA-XTPlus

Table 1aDescriptive statistics of pH values for different treatments [0W-5min (CNT5M), 0W-10min (CNT10M), 30W-5min (30W5M), 30W-10min (30W10M), 60W-5min (60W5M),60 W-10 min (60W10M), 90 W-5 min (90W5M), 90 W-10 min (90W10M)] during storage.

Storage time (week)/treatment time (min)/pH value

0 Week 1 Week 2 Weeks 3 Weeks 4 Weeks

5M 10M 5M 10M 5M 10M 5M 10M 5M 10M

CNT 3.49 � 0.02 3.49 � 0.02 3.64 � 0.03 3.64 � 0.02 3.65 � 0.02 3.64 � 0.03 3.67 � 0.04 3.67 � 0.04 3.70 � 0.03 3.70 � 0.0430W 3.49 � 0.02 3.49 � 0.02 3.56 � 0.02 3.54 � 0.02 3.55 � 0.01 3.54 � 0.05 3.57 � 0.02 3.56 � 0.01 3.61 � 0.04 3.61 � 0.0160W 3.49 � 0.02 3.49 � 0.02 3.54 � 0.02 3.61 � 0.02 3.52 � 0.06 3.58 � 0.01 3.57 � 0.03 3.64 � 0.02 3.66 � 0.01 3.66 � 0.0990W 3.49 � 0.02 3.49 � 0.02 3.61 � 0.02 3.60 � 0.02 3.70 � 0.01 3.69 � 0.02 3.69 � 0.04 3.65 � 0.02 3.73 � 0.05 3.67 � 0.01

Data are means � SD of three replicates.

Table 1bEffect of different treatments [0 W-5 min (CNT5M), 0 W-10 min (CNT10M), 30 W-5 min (30W5M), 30 W-10 min (30W10M), 60 W-5 min (60W5M), 60 W-10 min (60W10M),90 W-5 min (90W5M), 90 W-10 min (90W10M)] on pH value (storage time � treatment power interaction) of strawberry during storage.

Storage time (week)/pH value


CNT 3.49 � 0.01Aa 3.64 � 0.02Ba 3.65 � 0.02Ba 3.67 � 0.03Ba 3.70 � 0.03Ba30W 3.49 � 0.01Aa 3.55 � 0.02ABa 3.54 � 0.03ABb 3.56 � 0.01ABb 3.61 � 0.02Ba60W 3.49 � 0.01Aa 3.57 � 0.03ABCa 3.55 � 0.04ABb 3.61 � 0.04BCab 3.66 � 0.05Ca90W 3.49 � 0.01Aa 3.60 � 0.04Ba 3.70 � 0.01Ba 3.67 � 0.03Ba 3.70 � 0.04Ba

AeCMeans in the same row with different letters are significantly different (p < 0.05). Data are means � SD of three replicates.aecMeans in the same column with different letters are significantly different (p < 0.05). Mean separation was performed by Tukey test.

Table 1cEffect of different treatments [0 W-5 min (CNT5M), 0 W-10 min (CNT10M), 30 W-5 min (30W5M), 30 W-10 min (30W10M), 60 W-5 min (60W5M), 60 W-10 min(60W10M), 90W-5min (90W5M), 90W-10min (90W10M)] on pH value (treatmenttime � treatment power Interaction) of strawberry.

Treatment power (W)/pH value

5M 10M

CNT 3.63 � 0.08Aa 3.63 � 0.07Aa30W 3.56 � 0.04Ab 3.55 � 0.04Ab60W 3.56 � 0.06Ab 3.60 � 0.07Aa90W 3.64 � 0.09Aa 3.62 � 0.07Aa

AeCMeans in the same rowwith different letters are significantly different (p< 0.05).Data are means � SD of three replicates.aecMeans in the same column with different letters are significantly different(p < 0.05). Mean separation was performed by Tukey test.

Table 2bEffect of different storage times on total soluble solid content of strawberry duringstorage.

Storage time (week)/total soluble solid value


7.03 � 0.50A 6.36 � 0.38B 5.82 � 0.40C 5.64 � 0.32CD 5.45 � 0.24D

AeCMeans in the same rowwith different letters are significantly different (p< 0.05).Data are means � SD of three replicates. Mean separation was performed by Tukeytest.

Table 2cEffect of different treatment powers [0 W (CNT), 30 W (30W), 60 W (60W), 90 W(90W)] on total soluble solid content of strawberry during storage.

Treatment power (W)/total soluble solid value

CNT 30W 60W 90W

5.91 � 0.65A 6.36 � 0.58B 6.14 � 0.65AB 5.84 � 0.75A


M.S. Aday et al. / LWT - Food Science and Technology 52 (2013) 93e101 95

texture analyzer (Stable Micro Systems Ltd., UK) using a 10 mmdiameter cylinder plunger probe (SMS-P/10 CYL Delrin). Analyseswere performed under the following conditions: pre-test speed of5.0 mm/s, test speed of 1.0 mm/s and post-test speed of 8.0 mm/s;penetration distance of 4 mm, and a rest period of 5 s between twocycles; trigger force of 1.0 N. Acquired data’s were processed withTexture Exponent 32 by using PC software (Caner et al., 2008).

2.8. Decay incidence of strawberry

Strawberry with lesions of gray mold was assessed visually.Results were expressed as percentage of infected strawberry for

Table 2aDescriptive statistics of total soluble solid content values for different treatments [0W-5m60 W-5 min (60W5M), 60 W-10 min (60W10M), 90 W-5 min (90W5M), 90 W-10 min (9

Storage time (week)/treatment time (min)/total soluble solid value

0 Week 1 Week 2 Weeks

5M 10M 5M 10M 5M

CNT 7.03 � 0.68 7.03 � 0.68 5.96 � 0.19 5.94 � 0.15 5.64 � 0.1630W 7.03 � 0.68 7.03 � 0.68 6.86 � 0.13 6.74 � 0.28 6.43 � 0.0560W 7.03 � 0.68 7.03 � 0.68 6.72 � 0.18 6.24 � 0.26 6.07 � 0.0890W 7.03 � 0.68 7.03 � 0.68 6.35 � 0.02 6.05 � 0.21 5.34 � 0.17


each group (Aday, Caner, & Rahvalı, 2011; Pérez, Sanz, Ríos, Olías, &Olías, 1999).

2.9. FT-NIR measurements

Strawberries were scanned in transmission and reflectancemodes with using a Bruker multi-purpose analyzer (MPA) FT-NIR

in (CNT5M), 0W-10min (CNT10M), 30W-5min (30W5M), 30W-10min (30W10M),0W10M)] during storage.

3 Weeks 4 Weeks

10M 5M 10M 5M 10M

5.63 � 0.16 5.56 � 0.02 5.55 � 0.02 5.39 � 026 5.38 � 0.266.22 � 0.34 6.03 � 0.10 5.86 � 0.10 5.70 � 0.35 5.72 � 0.085.82 � 0.12 6.08 � 0.10 5.48 � 0.16 5.54 � 0.08 5.34 � 0.405.44 � 0.38 5.34 � 0.18 5.26 � 0.06 5.35 � 0.03 5.20 � 0.01

Table

3aDescriptive

statistics

ofL*

values

fordifferenttrea

tmen

ts[0

W-5

min

(CNT5

M),0W

-10min

(CNT1

0M),30

W-5

min

(30W

5M),30

W-10min

(30W

10M),60

W-5

min

(60W

5M),60

W-10min

(60W

10M),90

W-5

min

(90W

5M),

90W

-10min

(90W

10M)]

duringstorag

e.

Storag

etime(w

eek)/treatmen

ttime(m

in)/L*

value

0W

eek

1W

eek

2W

eeks

3W

eeks

4W

eeks

5M10

M5M

10M

5M10

M5M

10M

5M10

M

CNT

35.55�

1.52

35.55�

1.52

31.87�

0.14

30.34�

0.29

31.02�

2.06

30.51�

2.06

30.73�

1.42

30.12�

1.57

29.86�

0.01

29.00�

0.01

30W

35.55�

1.52

35.55�

1.52

33.07�

0.08

33.53�

0.90

32.55�

0.39

31.77�

0.69

32.16�

0.61

31.78�

1.43

31.71�

0.45

31.90�

0.57

60W

35.55�

1.52

35.55�

1.52

32.91�

0.87

32.65�

0.52

32.57�

0.28

31.74�

1.56

31.80�

0.49

31.26�

2.66

31.45�

0.02

30.88�

0.08

90W

35.55�

1.52

35.55�

1.52

31.54�

0.56

31.27�

0.05

31.17�

0.83

30.95�

1.67

30.59�

0.62

30.17�

0.01

29.73�

0.41

29.94�

0.70

Dataaremea

ns�

SDof

threereplic

ates.

TE

A

D

TE(

A

D


spectrometer (Bruker Optics, GmbH, Ettlingen, Germany) equip-ped with an InGaAs detectors working in 780e2500 nm (TE-InGaAs internal for reflectance and RT-InGaAs external for trans-mittance) and 20-W high intensity tungstenehalogen bulb wasused as light source. All spectra were processed with OPUS soft-ware (Bruker Optics GmbH, Germany). Scanning parameters were32 scans in 15.32 s and 128 scan in 62 s for reflectance andtransmission spectrums, respectively (Aday et al., 2011).

2.10. Statistical analysis

Three-way ANOVA was performed to determine ultrasoundpower and treatment time effects on physical and chemicalattributes of strawberry for different storage times. In all treat-ments, three replicates per treatment were used. We have useda linear model with up to threefold (three ultrasound power level,two treatment time and four storage time) interactions. Tukeymultiple comparison test was used to determine the differencesbetween means (p < 0.05). Statistical analyses were carried outusing SAS 9.1.3 statistical software.

3. Results and discussion

3.1. Gas composition

Preserving quality and extending shelf life of fresh productsdepend on maintaining optimum levels of O2 and CO2 in packagein order to decrease the metabolic activity (Montanez, Rodríguez,Mahajan, & Frías, 2010). The gas composition results obtainedfrom the inside package of different treatments are shown inFig. 1(A). Increased storage time resulted in more decrease inoxygen concentration for 90W5M and 90W10M compared withCNT5M and CNT10M.

Fig. 1(B) presents the carbon dioxide concentration inside thepackages of different treatments. Statistically significant differ-ences were found between CNT, 90Wand 30W, 60W treatments.This finding is in agreement with the findings of Zhao, Feng, and Li(2007) which showed that ultrasound treatment with modifiedatmosphere packaging decreased the respiration rate and CO2accumulation of fragrant pear.

3.2. pH

Table 1a shows the pH values of strawberries with differenttreatments during storage. Statistical analyses revealed thatinteractions of three factors (Day*Power*Time) were not

able 3bffect of different storage times on L* value of strawberry during storage.

Storage time (week)/L* value


35.55 � 1.11A 32.15 � 1.10B 31.53 � 1.24BC 31.07 � 1.24BC 30.56 � 1.07C

eCMeans in the same row with different letters are significantly different (p < 0.05).ataaremeans� SDof three replicates.MeanseparationwasperformedbyTukey test.

able 3cffect of different treatment powers [0 W (CNT), 30 W (30W), 60 W (60W), 90 W90W)] on L* value of strawberry during storage.

Treatment power (W)/L* value

CNT 30W 60W 90W

31.45 � 2.42A 32.96 � 1.60B 32.63 � 1.85B 31.64 � 2.19A

eCMeans in the same row with different letters are significantly different (p < 0.05).ataaremeans� SDof three replicates.MeanseparationwasperformedbyTukey test.

Table 4aDescriptive statistics of a* values for different treatments [0W-5min (CNT5M), 0W-10min (CNT10M), 30W-5min (30W5M), 30W-10min (30W10M), 60W-5min (60W5M),60 W-10 min (60W10M), 90 W-5 min (90W5M), 90 W-10 min (90W10M)] during storage.

Storage time (week)/treatment time (min)/a* value


5M 10M 5M 10M 5M 10M 5M 10M 5M 10M

CNT 36.13 � 1.82 36.13 � 1.82 32.08 � 0.10 31.72 � 0.09 30.21 � 1.15 29.98 � 1.44 29.12 � 1.55 28.27 � 1.00 28.03 � 1.58 27.50 � 2.1230W 36.13 � 1.82 36.13 � 1.82 35.25 � 0.38 34.91 � 0.96 34.35 � 2.93 35.86 � 0.79 32.35 � 0.31 32.82 � 0.27 30.75 � 1.47 30.49 � 1.3460W 36.13 � 1.82 36.13 � 1.82 35.46 � 1.70 34.22 � 0.61 33.90 � 4.04 33.42 � 0.72 32.25 � 0.83 30.69 � 0.46 31.18 � 0.94 29.81 � 0.0390W 36.13 � 1.82 36.13 � 1.82 31.84 � 1.87 32.28 � 0.75 30.64 � 1.01 30.64 � 1.00 28.91 � 0.47 29.29 � 1.02 28.28 � 0.28 27.23 � 0.84


Table 4bEffect of different storage times on a* value of strawberry during storage.

Storage time (week)/a* value


36.13 � 1.33A 33.47 � 1.75B 32.26 � 2.72B 30.46 � 1.85C 29.16 � 1.77C


Table 4cEffect of different treatment powers [0 W (CNT), 30 W (30W), 60 W (60W), 90 W(90W)] on a* value of strawberry during storage.

Treatment power (W)/a* value

CNT 30W 60W 90W

30.92 � 3.21A 33.90 � 2.34B 33.32 � 2.52B 31.04 � 3.12A



0 1 2 3 4 5

Dec

ay In

cide

nce

(%)

0

5

10

15

20

25

Fig. 2. Effect of different treatments [ 0 W-5 min (CNT5M), 0 W-10 min(CNT10M), 30W-5 min (30W5M), 30 W-10 min (30W10M), 60W-5 min(60W5M), 60 W-10 min (60W10M), 90 W-5 min (90W5M), 90 W-10 min (90W10M)] on growth of mold during storage.


significantly important. However, significant levels of interactionswere found between Day*Power (Table 1b) and Power*Time(Table 1c). In contrast to 90 W and CNT treatments, 30 W and 60Whad the lower pH values of 3.56 and 3.61, respectively (Table 1b).From the data in Table 1c, it can be seen that there was a significantdifference between 30 W and other treatments for 10 min. Apossible explanation for this difference in pH values might berelated to high CO2 levels inside 90 W and CNT packages. High CO2

accumulation is an indicator of the high respiration and degrada-tion rates of organic acids (Almenar et al., 2007; Holcroft & Kader,1999; Zhao et al., 2007). These findings showed that 30 W and60 W ultrasound treatments were effective in maintaining pH ofstrawberries during storage.

3.3. Total soluble solids

Total soluble solids (TSS) play an important role in affecting fruitquality and consumer acceptability. Statistical analyses showedthat interactions of factors (including two and three factors) werenot significantly important. But main effects of storage time andultrasound power were statistically significant (Tables 2a and 2b).TSS content of 30 W treatment was statistically different from theCNT and 90 W treatment. Possible explanation for this might bethat 90 W treatment distorted and disrupted the cell structures ofstrawberry and formed microscopic channels which results inwater loss (Fernandes, Gallão, & Rodrigues, 2009) (Table 2c).

3.4. Color

Color is an important parameter for determining the quality offresh products and the quantity of anthocyanins which known asa responsible compound of attractive, red color of strawberry(Rodrigo, Van Loey, & Hendrickx, 2007). Changes in L* values fordifferent treatments during storage are shown in Table 3a. Thestatistical analyses showed that interactions of factors (includingtwo and three factors) were not significantly important. On theother hand, main effects of storage time and ultrasound powerwere statistically significant (Tables 3b and 3c). Statisticallysignificance was found between 90 W and 30e60 W treatments.The results of L* values indicated that 30 W and 60 W treatmentswere effective to preserve the bright color of strawberry whencompared with CNT and 90 W.

Table 4a shows the changes in a* values for different treatmentsduring storage. Statistical analyses showed that interactions offactors (including two and three factors) were not significantlyimportant. However, main effects of storage time and ultrasoundpower were statistically significant (Tables 4b and 4c). After oneweek of storage, a* values of strawberry dropped distinctly, andremained steady in the second and third weeks (Table 4b). It ispossible that 90 W treatment had adverse effect on the anthocya-nins stability of strawberry due to cavitations including theformation of hydroxyl radicals (Tiwari, Patras, Brunton, Cullen, &O’Donnell, 2010).

3.5. Decay incidence

Gray mold is a common and serious disease which can causesignificant amount of loss during storage, transportation andmarketing of strawberries (Zhang et al., 2007). Fig. 2 shows thatthere has been a marked increase in the number of infectedstrawberries during storage. No significant differences foundbetween ultrasound treatments. However, there was a significant


0 1 2 3 4 5

Firm

ness

(g)

200

400

600

800


0 1 2 3 4 5

Adhe

sive

ness

(g.s

)

3,003,253,503,754,004,254,504,755,005,255,505,756,00


0 1 2 3 4 5

Sprin

gnes

s (D

imen

sion

less

)

0,45

0,50

0,55

0,60

0,65

0,70


0 1 2 3 4 5

Coh

esiv

enes

s (D

imen

sion

less

)

0,25

0,30

0,35

0,40

0,45

0,50

0,55


0 1 2 3 4 5

Gum

min

ess

(g)

100

200

300

400


0 1 2 3 4 5

Che

win

ess

(g)

50

100

150

200

250

300


0 1 2 3 4 5

Res

ilienc

e (D

imen

sion

less

)

0,14

0,16

0,18

0,20

0,22

0,24

0,26

A

C

G

E F

D

B

Fig. 3. Effect of different treatments [ 0 W-5 min (CNT5M), 0 W-10 min (CNT10M), 30 W-5 min (30W5M), 30 W-10 min (30W10M), 60 W-5 min (60W5M),60 W-10 min (60W10M), 90 W-5 min (90W5M), 90 W-10 min (90W10M)] on texture parameters [(A) firmness, (B) adhesiveness, (C) springness, (D) cohesiveness, (E)

gumminess, (F) chewiness, and (G) resilience] during storage.



difference between control and ultrasound treatments. It ispossible that ultrasound treatments punctured cell walls anddamaged membrane functions of molds (Guerrero, Tognon, &Alzamora, 2005). Our results are in good agreement with Caoet al. (2010) who found that ultrasonic treatment reduced thefruit decay in strawberry.

3.6. Texture profile analysis (TPA)

Texture is a main characteristic of strawberry related to thequality. Texture gives comprehensive information about micro-structure of foods as well as cell wall, middle lamella and turgorpressure (Fraeye et al., 2010). Firmness, cohesiveness, springiness,gumminess, chewiness and resilience values of strawberryincreased while adhesiveness values decreased during storage timein all treatments (Fig. 3).

Firmness can be attributed to the physical anatomy of tissue, cellsize, shape, cell wall strength and intercellular adhesion (Toivonen& Brummell, 2008). The higher firmness values were obtained withtreatment of 30W5M and 30W10Mwhereas the lower values wereobtained with 90W5M and 90W10M (Fig. 3(A)). The observed

Fig. 4. Effect of different treatments [0 W-5 min (CNT5M), 0 W-10 min (CNT10M), 30 W-5 m90 W-5 min (90W5M), 90 W-10 min (90W10M)] on FT-NIR spectra’s at reflectance and tra

decrease in firmness for 90 W treatments could be attributed todestructive effect of high power ultrasound on stability of cell wallwhich results in loss of water (Fernandes et al., 2009).

The term adhesiveness has come to be used to refer to surfacecharacteristic which related with adhesive and cohesive forces(Rahman & Al-Farsi, 2005). Higher values for 90 W treatment maybe due to adverse effect (expansion and contraction) of highacoustic intensity in solid matrix (Fig. 3(B)) (García-Pérez, Cárcel,Benedito, & Mulet, 2007).

Springiness can be defined as the rate that deformed food goesback to its undeformed condition (de Huidobro, Miguel, Blazquez, &Onega, 2005). The Fig. 3(C) indicates that springiness values of CNTand 90 W treatments were lower than 30 W and 60 W treatmentsduring storage. It is possible that 90 W treatments destroyed thestructural integrity of membrane, cell walls and cellecell adhesion(Hernandez-Munoz, Almenar, Del Valle, Velez, & Gavara, 2008).

The term cohesiveness refers to strength of internal bonds anddifficulty degree in breaking down the internal structure (Yanget al., 2007). At the end of the storage, CNT and 90 W treatmentshave the lower cohesiveness values compared with other treat-ments (Fig. 3(D)). Possible explanation for this might be that high

in (30W5M), 30 W-10 min (30W10M), 60 W-5 min (60W5M), 60 W-10 min (60W10M),nsmission modes during storage.


power ultrasound created the microscopic channels with reducingthe diffusion boundary layer (Azoubel, Baima, Amorim, & Oliveira,2010).

The use of term gumminess is related to force required to chewor swallow to food. It was decreased during the storage for allgroups (Fig. 3(E)). The observed reduction of gumminess values forCNT and 90 W treatment could be attributed to the high hydrolysisreactions rate and adverse effect of high power ultrasound on theturgor pressure (Del-Valle, Hernandez-Munoz, Guarda, & Galotto,2005).

Chewiness can be defined as the energy for masticating semi-solid sample (Huang, Kennedy, Li, Xu, & Xie, 2007). Fig. 3(F)showed that with high power ultrasound (90 W) less energy wasneeded to masticate the sample. This result may be explained bythe fact that high power acoustic energy destroyed the primary cellwall and middle lamella more than that of the 30 W and 60 Wtreatments.

Resilience is the energy for fighting back to its original state(Rahman & Al-Farsi, 2005). The values of 30Wand 60W treatmentsdecreased slightly whereas the values of CNT and 90 W droppedsharply during storage (Fig. 3(G)).

The findings of TPA analysis showed that 30 W and 60 Wtreatments maintained the TPA parameters better than that of CNTand 90W treatments. It seems possible that high power ultrasoundhad destructive effect on cell wall constituents of strawberry.

3.7. Fourier transform near infrared (FT-NIR) spectroscopyevaluation

FT-NIR is a novel approach to estimate the quality attributes offood using specific wavelengths between 750 nm and 2500 nm(Chen, Cai, Wan, & Zhao, 2011). It is a rapid, effective and nonde-structive method for determining functional groups (OeH, CeH,NeH) and monitoring the changes of sugar and water in foods(Louw & Theron, 2010).

The results obtained from the FT-NIR analysis for reflectance andtransmission modes of treatments are shown in Fig. 4a and b. Thebands around 8454 and 5623 cm�1 are caused by the sugars andbands around 10,244 cm�1 can be attributed to water content (DiEgidio et al., 2009). At the beginning of the storage, absorptionspectrum showed high absorbance for sugar and water content dueto freshness quality, as expected. Increased storage time resulted indecrease of absorption bands for all treatments. At the end of thestorage, absorption peaks around 8454 cm�1 dropped significantlyfor CNT and 90 W when compared with other treatments. Corre-lation was found between these results and TSS values. The lowestpeaks were observed around 10,244 cm�1 for CNT and 90 Wtreatments due to the high respiration rate and metabolic activityof CNT group and destructive effect of high power ultrasound oncell wall and cellecell adhesion which results with greater loss ofwater.

4. Conclusions

This paper has given an account of and the reasons for the use ofultrasound in the food industry. This study was designed todetermine the effects of different ultrasound powers (30 W, 60 W,90 W) and treatment times (5M, 10M) on quality of strawberry.Contrary to expectations, this study did not find a significantdifference between treatment times. It was however found that,ultrasound power between 30Wand 60W could be used to extendshelf life of strawberry. It was observed that the high powerultrasound (90 W or higher) presents detrimental effects onstrawberry quality. The empirical findings in this study providea new understanding of ultrasound power. Finally, this research has

shown that ultrasound power should be adjusted depending on thedesired effect. Second major finding was that FT-NIR technologyoffers the nondestructive evaluation of some quality attributes assugar and water content. Further researches in this topic regardingthe role of different treatment times would be great help inunderstanding the different effects on quality of fruits andvegetables.

Acknowledgments

This research was conducted with financial support from theCOMU-BAP Project (Code 2010/151). The authors would like tothank Dr. Onder Ayyıldız for providing ultrasound system and FeritTemizkan for the supply of strawberries used in this study.

References

Aday, M. S., & Caner, C. (2010). Understanding the effects of various ediblecoatings on the storability of fresh cherry. Packaging Technology and Science,23(8), 441e456.

Aday, M. S., Caner, C., & Rahvalı, F. (2011). Effect of oxygen and carbon dioxideabsorbers on strawberry quality. Postharvest Biology and Technology, 62(2),179e187.

Almenar, E., Del-Valle, V., Hernandez-Munoz, P., Lagaron, J. M., Catala, R., &Gavara, R. (2007). Equilibrium modified atmosphere packaging of wild straw-berries. Journal of the Science of Food and Agriculture, 87(10), 1931e1939.

Azoubel, P. M., Baima, M. D. A. M., Amorim, M. D. R., & Oliveira, S. S. B. (2010). Effectof ultrasound on banana cv Pacovan drying kinetics. Journal of Food Engineering,97(2), 194e198.

Caner, C., & Aday, M. S. (2009). Maintaining quality of fresh strawberries throughvarious modified atmosphere packaging. Packaging Technology and Science,22(2), 115e122.

Caner, C., Aday, M., & Demir, M. (2008). Extending the quality of fresh strawberriesby equilibrium modified atmosphere packaging. European Food Research andTechnology, 227(6), 1575e1583.

Cao, S., Hu, Z., Pang, B., Wang, H., Xie, H., & Wu, F. (2010). Effect of ultrasoundtreatment on fruit decay and quality maintenance in strawberry after harvest.Food Control, 21(4), 529e532.

Chen, Q., Cai, J., Wan, X., & Zhao, J. (2011). Application of linear/non-linear classi-fication algorithms in discrimination of pork storage time using Fourier trans-form near infrared (FT-NIR) spectroscopy. LWT e Food Science and Technology,44(10), 2053e2058.

Chen, F., Liu, H., Yang, H., Lai, S., Cheng, X., Xin, Y., et al. (2011). Quality attributes andcell wall properties of strawberries (Fragaria annanassa Duch.) under calciumchloride treatment. Food Chemistry, 126(2), 450e459.

Correia, P. J., Pestana, M., Martinez, F., Ribeiro, E., Gama, F., Saavedra, T., et al. (2011).Relationships between strawberry fruit quality attributes and crop load. ScientiaHorticulturae, 130(2), 398e403.

Del-Valle, V., Hernandez-Munoz, P., Guarda, A., & Galotto, M. J. (2005). Develop-ment of a cactus-mucilage edible coating (Opuntia ficus indica) and its appli-cation to extend strawberry (Fragaria ananassa) shelf-life. Food Chemistry, 91(4),751e756.

Di Egidio, V., Sinelli, N., Limbo, S., Torri, L., Franzetti, L., & Casiraghi, E. (2009).Evaluation of shelf-life of fresh-cut pineapple using FT-NIR and FT-IR spec-troscopy. Postharvest Biology and Technology, 54(2), 87e92.

Dotto, M. C., Pombo, M. A., Martínez, G. A., & Civello, P. M. (2011). Heat treatmentsand expansin gene expression in strawberry fruit. Scientia Horticulturae, 130(4),775e780.

Feng, H., Barbosa-Canovas, G., & Weiss, J. (2011). Ultrasound technologies for food andbioprocessing. Springer.

Fernandes, F. A. N., Gallão, M. I., & Rodrigues, S. (2009). Effect of osmosis andultrasound on pineapple cell tissue structure during dehydration. Journal ofFood Engineering, 90(2), 186e190.

Fraeye, I., Knockaert, G., Van Buggenhout, S., Duvetter, T., Hendrickx, M., & VanLoey, A. (2010). Enzyme infusion prior to thermal/high pressure processing ofstrawberries: mechanistic insight into firmness evolution. Innovative FoodScience & Emerging Technologies, 11(1), 23e31.

García-Pérez, J. V., Cárcel, J. A., Benedito, J., & Mulet, A. (2007). Power ultrasoundmass transfer enhancement in food drying. Food and Bioproducts Processing,85(3), 247e254.

Guerrero, S., Tognon, M., & Alzamora, S. M. (2005). Response of Saccharomycescerevisiae to the combined action of ultrasound and low weight chitosan. FoodControl, 16(2), 131e139.

Hernandez-Munoz, P., Almenar, E., Del Valle, V., Velez, D., & Gavara, R. (2008). Effectof chitosan coating combined with postharvest calcium treatment on straw-berry (Fragaria � ananassa) quality during refrigerated storage. Food Chemistry,110(2), 428e435.

Holcroft, D. M., & Kader, A. A. (1999). Controlled atmosphere-induced changes in pHand organic acid metabolism may affect color of stored strawberry fruit. Post-harvest Biology and Technology, 17(1), 19e32.


Huang, M., Kennedy, J. F., Li, B., Xu, X., & Xie, B. J. (2007). Characters of rice starch gelmodified by gellan, carrageenan, and glucomannan: a texture profile analysisstudy. Carbohydrate Polymers, 69(3), 411e418.

de Huidobro, F. R., Miguel, E., Blazquez, B., & Onega, E. (2005). A comparisonbetween two methods (Warner-Bratzler and texture profile analysis) for testingeither raw meat or cooked meat. Meat Science, 69(3), 527e536.

Louw, E. D., & Theron, K. I. (2010). Robust prediction models for quality parametersin Japanese plums (Prunus salicina L.) using NIR spectroscopy. PostharvestBiology and Technology, 58(3), 176e184.

Manas, P., Pagan, R., & Raso, J. (2000). Predicting lethal effect of ultrasonic wavesunder pressure treatments on Listeria monocytogenes ATCC 15313 by powermeasurements. Journal of Food Science, 65(4), 663e667.

Montanez, J. C., Rodríguez, F. A. S., Mahajan, P. V., & Frías, J. M. (2010). Modellingthe effect of gas composition on the gas exchange rate in perforation-mediated modified atmosphere packaging. Journal of Food Engineering,96(3), 348e355.

Pérez, A. G., Sanz, C., Ríos, J. J., Olías, R., & Olías, J. M. (1999). Effects of ozonetreatment on postharvest strawberry quality. Journal of Agricultural and FoodChemistry, 47(4), 1652e1656.

Rahman, M. S., & Al-Farsi, S. A. (2005). Instrumental texture profile analysis (TPA) ofdate flesh as a function of moisture content. Journal of Food Engineering, 66(4),505e511.

Rodrigo, D., Van Loey, A., & Hendrickx, M. (2007). Combined thermal and highpressure colour degradation of tomato puree and strawberry juice. Journal ofFood Engineering, 79(2), 553e560.

Sagong, H. G., Lee, S. Y., Chang, P. S., Heu, S., Ryu, S., Choi, Y. J., et al. (2011). Combinedeffect of ultrasound and organic acids to reduce Escherichia coli O157:H7,Salmonella Typhimurium, and Listeria monocytogenes on organic fresh lettuce.International Journal of Food Microbiology, 145(1), 287e292.

Tiwari, B. K., Patras, A., Brunton, N., Cullen, P. J., & O’Donnell, C. P. (2010). Effect ofultrasound processing on anthocyanins and color of red grape juice. UltrasonicsSonochemistry, 17(3), 598e604.

Toivonen, P. M. A., & Brummell, D. A. (2008). Biochemical bases of appearance andtexture changes in fresh-cut fruit and vegetables. Postharvest Biology andTechnology, 48(1), 1e14.

Yang, Z. F., Cao, S. F., Cai, Y. T., & Zheng, Y. H. (2011). Combination of salicylic acid andultrasound to control postharvest blue mold caused by Penicillium expansum inpeach fruit. Innovative Food Science & Emerging Technologies, 12(3), 310e314.

Yang, Z. F., Zheng, Y. H., Cao, S. F., Tang, S. S., Ma, S. J., & Li, N. (2007). Effects ofstorage temperature on textural properties of Chinese bayberry fruit. Journal ofTexture Studies, 38(1), 166e177.

Zhang, H., Wang, L., Dong, Y., Jiang, S., Cao, J., & Meng, R. (2007). Postharvest bio-logical control of gray mold decay of strawberry with Rhodotorula glutinis.Biological Control, 40(2), 287e292.

Zhao, Y. X., Feng, Z. S., & Li, X. W. (2007). Effect of ultrasonic and MA packagingmethod on quality and some physiological changes of fragrant pear. Journal ofXinjiang Agricultural University, 30, 61e63.

Zhou, B., Feng, H., & Luo, Y. (2009). Ultrasound enhanced sanitizer efficacy inreduction of Escherichia coli O157:H7 population on spinach leaves. Journal ofFood Science, 74(6), M308eM313.

Documents

An innovative technique for extending shelf life of strawberry: Ultrasound