An innovative technique for extending shelf life of strawberry: Ultrasound

An innovative technique for extending shelf life of strawberry: Ultrasound

LWT - Food Science and Technology 52 (2013) 93e101 Contents lists available at SciVerse ScienceDirect LWT - Food Science and Technology journal home...

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

Contents lists available at SciVerse ScienceDirect

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, ** a b

Department of Food Engineering, Çanakkale Onsekiz Mart University, Engineering-Architecture Faculty, Terzioglu Kampusu, 017020 Canakkale, Turkey Department of Agricultural Machinery, Çanakkale Onsekiz Mart University, 17020 Canakkale, Turkey

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 May 2012 Received in revised form 14 August 2012 Accepted 13 September 2012

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 present study was designed to determine the effect of different ultrasound powers (30 W, 60 W, 90 W) and treatment times (5 min, 10 min) on quality of strawberry. Oxygen concentration inside packages of strawberries 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 during the storage. Attributes such as pH, total soluble solid content and color for the 30 W and 60 W treatments were better than CNT and 90 W treatments. Decay incidence analysis confirmed that all ultrasound treatments were effective to reduce mold growth. The 30 W and 60 W treatments maintained better textural properties compared with 90 W and CNT groups. FT-NIR analysis was used to quantify water and sugar content of strawberries. As a result, it was concluded that ultrasound power as high as 90 W resulted in detrimental effects on strawberry quality, while power levels between 30 W and 60 W had improved quality and can be used to extend shelf life of strawberry. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Strawberry Ultrasound FT-NIR Shelf life Texture

1. Introduction Strawberry is a delicate fruit with high nutritional quality and excellent organoleptic properties (Correia et al., 2011). However, this fruit has an extremely short postharvest life due to tenderness and susceptibility to mechanical injury, rapid dehydration, and infections by several pathogens (Chen, Liu, et al., 2011). Traditional methods used for preventing undesirable change of fruit attributes during storage, have a detrimental effect on nutritional properties and perceived quality. Therefore it’s necessary to find alternative methods to meet consumer expectations such as attractive sensorial properties and to satisfy public concern about the risks of new technologies for human health, environment, and food safety (Dotto, Pombo, Martínez, & Civello, 2011). One of the newest nonthermal methods to extend shelf life of fresh fruits and vegetables is using ultrasound. The ultrasound technology comparing with other novel techniques is perceived to be safer, non-toxic, environmental friendly and it is assumed as benign by public due to its use in hospitals for diagnostic imaging purposes (Feng, Barbosa-Canovas, & Weiss, 2011). The effect of

* Corresponding author. Tel.: þ90 2862180018/2607; fax: þ90 2862180541. ** Corresponding author. E-mail addresses: [email protected] (M.S. Aday), [email protected] (C. Caner). 0023-6438/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2012.09.013

ultrasound in food treatment depends on multiple factors including frequency and power of ultrasonic generator, medium temperature, pressure of the treatment, and characteristics of the treatment liquid (Manas, Pagan, & Raso, 2000). Numerous studies have attempted to explain the effect of ultrasound on fruits, vegetables, fruit juices and dairy products. Sagong et al. (2011) reported that combined treatment of ultrasound 30 W/L (40 kHz) and organic acids (malic, lactic and citric acid) were effective at pathogen reduction without 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 the quality after six days of storage at 20  C. Zhou, Feng, and Luo (2009) demonstrated that ultrasound (21.2 kHz, 200 W/L, 2 min) enhanced the reduction of Escherichia coli on spinach from 0.7 to 1.1 log CFU/g sample. Despite considerable amounts of literature have been published on ultrasound application, many of them were dealt with microbial quality rather than physical and chemical properties. Furthermore no scientific data are available regarding to the use of ultrasound with different treatment times and power. Therefore, the aim of this paper was to examine the effect of different ultrasound power and treatment times on physical (color, texture) and chemical properties (gas composition inside package, pH, total soluble solid, FT-NIR analysis) of strawberry during four weeks of storage at 4  C.

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2. Material and methods

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

2.1. Materials 2.5. Total soluble solids (TSS) Strawberry (Fragaria  ananassa) cv. Camarosa was harvested at commercially ripe stage by hand from a private farm in Yenice, Canakkale, Turkey. Fruits with signs of visual defect or physical damage were discarded. Selected fruits of uniform size and color were randomly distributed into 8 groups.

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

2.2. Treatments 2.6. Surface color

After treatments, strawberries were dried for 5 min, in order to remove excess water. Approximately, 200 g fruits were packaged in polylactic acid (PLA) trays which were supplied by Huhtamaki Istanbul Ambalaj Sanayi A.S. (Istanbul, Turkey). For each treatment, twenty packages of strawberries were prepared and four packages were used at each week for the same treatment. Strawberries were packaged under atmospheric conditions (21 kPa O2/0.03 kPa CO2) for 4 weeks at 4  C. Transmission rates of package film for O2, CO2 and H2O were 620 cm3 mil/m2 day atm, 2800 cm3 mil/m2 day atm and 340 g mil/m2 day, respectively. 2.3. Package gas composition Gas compositions (O2 and CO2) inside the packages were monitored with a gas analyzer (OxyBaby, HTK, Hamburg, Germany). The needle of gas analyzer was inserted to each package through an adhesive rubber septum to prevent air leaking from the package. After determining the gas composition, packages were used for further analysis (Aday & Caner, 2010). 2.4. pH measurement Strawberry was squeezed and the resulting juice was filtered through cheesecloth. Then pH of strawberry juice was determined

2.7. Texture profile analysis (TPA) Texture profile analysis was performed to determine firmness, springiness, cohesiveness, adhesiveness, gumminess, resilience and chewiness of strawberry. Samples were analyzed with TA-XTPlus

A

O2 Concentration (kPa)

1) Control: Strawberries immersed in distilled water for 5 min (CNT5M) 2) Control: Strawberries immersed in distilled water for 10 min (CNT10M) 3) 30 W ultrasound treatment: Strawberries treated with 30 W for 5 min (30W5M) 4) 30 W ultrasound treatment: Strawberries treated with 30 W for 10 min (30W10M) 5) 60 W ultrasound treatment: Strawberries treated with 60 W for 5 min (60W5M) 6) 60 W ultrasound treatment: Strawberries treated with 60 W for 10 min (60W10M) 7) 90 W ultrasound treatment: Strawberries treated with 90 W for 5 min (90W5M) 8) 90 W ultrasound treatment: Strawberries treated with 90 W for 10 min (90W10M)

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

23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0

1

2

3

4

5

4

5

Storage Time (Weeks)

B CO2 Concentration (kPa)

For the ultrasound treatments, three replicates of 500 g strawberries were immersed in 1000 ml glass beaker which was filled with distilled water for per treatment. Metallic probe (1.9 cm diameter of generator) (Vibra Cell505, Newtown, USA) was immersed in glass beaker to create acoustic cavitations. Strawberries 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 were calculated 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 be summarized as follows:

40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 0

1

2

3

Storage Time (Weeks) Fig. 1. Effect of different treatments [ 0 W-5 min (CNT5M), 0 W-10 min 30 W-5 min (30W5M), 30 W-10 min (30W10M), 60 W-5 min (CNT10M), 60 W-10 min (60W10M), 90 W-5 min (90W5M), 90 W(60W5M), 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) 93e101

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Table 1a Descriptive statistics of pH values for 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)] during storage. Storage time (week)/treatment time (min)/pH value 0 Week 5M CNT 30W 60W 90W

3.49 3.49 3.49 3.49

1 Week 10M

   

0.02 0.02 0.02 0.02

3.49 3.49 3.49 3.49

2 Weeks

5M    

0.02 0.02 0.02 0.02

3.64 3.56 3.54 3.61

10M    

0.03 0.02 0.02 0.02

3.64 3.54 3.61 3.60

3 Weeks

5M    

0.02 0.02 0.02 0.02

3.65 3.55 3.52 3.70

10M    

0.02 0.01 0.06 0.01

3.64 3.54 3.58 3.69

4 Weeks

5M    

0.03 0.05 0.01 0.02

3.67 3.57 3.57 3.69

10M    

0.04 0.02 0.03 0.04

3.67 3.56 3.64 3.65

5M    

0.04 0.01 0.02 0.02

3.70 3.61 3.66 3.73

10M    

0.03 0.04 0.01 0.05

3.70 3.61 3.66 3.67

   

0.04 0.01 0.09 0.01

Data are means  SD of three replicates.

Table 1b 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 pH value (storage time  treatment power interaction) of strawberry during storage. Storage time (week)/pH value 0 Week CNT 30W 60W 90W

3.49 3.49 3.49 3.49

   

1 Week

0.01Aa 0.01Aa 0.01Aa 0.01Aa

3.64 3.55 3.57 3.60

   

2 Weeks

0.02Ba 0.02ABa 0.03ABCa 0.04Ba

3.65 3.54 3.55 3.70

   

3 Weeks

0.02Ba 0.03ABb 0.04ABb 0.01Ba

3.67 3.56 3.61 3.67

   

4 Weeks

0.03Ba 0.01ABb 0.04BCab 0.03Ba

3.70 3.61 3.66 3.70

   

0.03Ba 0.02Ba 0.05Ca 0.04Ba

AeC

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

aec

Table 1c Effect of different treatments [0 W-5 min (CNT5M), 0 W-10 min (CNT10M), 30 W5 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 (treatment time  treatment power Interaction) of strawberry.

Table 2b Effect of different storage times on total soluble solid content of strawberry during storage. Storage time (week)/total soluble solid value

Treatment power (W)/pH value 5M CNT 30W 60W 90W

3.63 3.56 3.56 3.64

10M    

0.08Aa 0.04Ab 0.06Ab 0.09Aa

3.63 3.55 3.60 3.62

   

0 Week

1 Week

2 Weeks

3 Weeks

4 Weeks

7.03  0.50A

6.36  0.38B

5.82  0.40C

5.64  0.32CD

5.45  0.24D

AeC

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

0.07Aa 0.04Ab 0.07Aa 0.07Aa

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

Table 2c Effect 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

texture analyzer (Stable Micro Systems Ltd., UK) using a 10 mm diameter cylinder plunger probe (SMS-P/10 CYL Delrin). Analyses were performed under the following conditions: pre-test speed of 5.0 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 two cycles; trigger force of 1.0 N. Acquired data’s were processed with Texture Exponent 32 by using PC software (Caner et al., 2008).

CNT

30W

60W

90W

5.91  0.65A

6.36  0.58B

6.14  0.65AB

5.84  0.75A

AeC

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

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

2.8. Decay incidence of strawberry

2.9. FT-NIR measurements

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

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

Table 2a Descriptive statistics of total soluble solid content values for 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)] during storage. Storage time (week)/treatment time (min)/total soluble solid value 0 Week 5M CNT 30W 60W 90W

7.03 7.03 7.03 7.03

1 Week 10M

   

0.68 0.68 0.68 0.68

7.03 7.03 7.03 7.03

5M    

0.68 0.68 0.68 0.68

Data are means  SD of three replicates.

5.96 6.86 6.72 6.35

2 Weeks 10M

   

0.19 0.13 0.18 0.02

5.94 6.74 6.24 6.05

5M    

0.15 0.28 0.26 0.21

5.64 6.43 6.07 5.34

3 Weeks 10M

   

0.16 0.05 0.08 0.17

5.63 6.22 5.82 5.44

5M    

0.16 0.34 0.12 0.38

5.56 6.03 6.08 5.34

4 Weeks 10M

   

0.02 0.10 0.10 0.18

5.55 5.86 5.48 5.26

5M    

0.02 0.10 0.16 0.06

5.39 5.70 5.54 5.35

10M    

026 0.35 0.08 0.03

5.38 5.72 5.34 5.20

   

0.26 0.08 0.40 0.01

29.94  0.70 29.73  0.41 30.17  0.01 30.59  0.62

30.88  0.08 31.45  0.02 31.26  2.66 31.80  0.49

31.90  0.57 31.71  0.45 31.78  1.43

29.00  0.01

32.16  0.61

10M

29.86  0.01 30.12  1.57 30.73  1.42

5M 10M 5M

3 Weeks

4 Weeks

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

spectrometer (Bruker Optics, GmbH, Ettlingen, Germany) equipped with an InGaAs detectors working in 780e2500 nm (TEInGaAs internal for reflectance and RT-InGaAs external for transmittance) and 20-W high intensity tungstenehalogen bulb was used as light source. All spectra were processed with OPUS software (Bruker Optics GmbH, Germany). Scanning parameters were 32 scans in 15.32 s and 128 scan in 62 s for reflectance and transmission spectrums, respectively (Aday et al., 2011). 2.10. Statistical analysis Three-way ANOVA was performed to determine ultrasound power and treatment time effects on physical and chemical attributes of strawberry for different storage times. In all treatments, three replicates per treatment were used. We have used a linear model with up to threefold (three ultrasound power level, two treatment time and four storage time) interactions. Tukey multiple comparison test was used to determine the differences between means (p < 0.05). Statistical analyses were carried out using SAS 9.1.3 statistical software. 3. Results and discussion

30.95  1.67 31.27  0.05

3.2. pH Table 1a shows the pH values of strawberries with different treatments during storage. Statistical analyses revealed that interactions of three factors (Day*Power*Time) were not

31.54  0.56

32.91  0.87

Preserving quality and extending shelf life of fresh products depend on maintaining optimum levels of O2 and CO2 in package in order to decrease the metabolic activity (Montanez, Rodríguez, Mahajan, & Frías, 2010). The gas composition results obtained from the inside package of different treatments are shown in Fig. 1(A). Increased storage time resulted in more decrease in oxygen concentration for 90W5M and 90W10M compared with CNT5M and CNT10M. Fig. 1(B) presents the carbon dioxide concentration inside the packages of different treatments. Statistically significant differences were found between CNT, 90 W and 30 W, 60 W treatments. This finding is in agreement with the findings of Zhao, Feng, and Li (2007) which showed that ultrasound treatment with modified atmosphere packaging decreased the respiration rate and CO2 accumulation of fragrant pear.

31.17  0.83

31.74  1.56 32.65  0.52

32.57  0.28

31.77  0.69 32.55  0.39 33.07  0.08

31.87  0.14

30.34  0.29

33.53  0.90

30.51  2.06 31.02  2.06

2 Weeks

10M 5M

1 Week

10M

5M

3.1. Gas composition

Storage time (week)/L* value 0 Week Data are means  SD of three replicates.

35.55  1.52 35.55  1.52 90W

35.55  1.52 35.55  1.52 60W

35.55  1.52 35.55  1.52 30W

35.55  1.52 35.55  1.52 CNT

10M 5M

Table 3b Effect of different storage times on L* value of strawberry during storage.

0 Week

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

Table 3a Descriptive statistics of L* values for 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)] during storage.

96

1 Week

2 Weeks

3 Weeks

4 Weeks

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

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

Table 3c Effect of different treatment powers [0 W (CNT), 30 W (30W), 60 W (60W), 90 W (90W)] 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

AeC

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

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

97

Table 4a Descriptive statistics of a* values for 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)] during storage. Storage time (week)/treatment time (min)/a* value 0 Week

1 Week

5M CNT 30W 60W 90W

36.13 36.13 36.13 36.13

10M    

1.82 1.82 1.82 1.82

36.13 36.13 36.13 36.13

2 Weeks

5M    

1.82 1.82 1.82 1.82

32.08 35.25 35.46 31.84

10M    

0.10 0.38 1.70 1.87

31.72 34.91 34.22 32.28

5M    

0.09 0.96 0.61 0.75

30.21 34.35 33.90 30.64

3 Weeks 10M

   

1.15 2.93 4.04 1.01

29.98 35.86 33.42 30.64

5M    

1.44 0.79 0.72 1.00

4 Weeks 10M

29.12 32.35 32.25 28.91

   

1.55 0.31 0.83 0.47

28.27 32.82 30.69 29.29

5M    

1.00 0.27 0.46 1.02

28.03 30.75 31.18 28.28

10M    

1.58 1.47 0.94 0.28

27.50 30.49 29.81 27.23

   

2.12 1.34 0.03 0.84

Data are means  SD of three replicates.

significantly important. However, significant levels of interactions were found between Day*Power (Table 1b) and Power*Time (Table 1c). In contrast to 90 W and CNT treatments, 30 W and 60 W had 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 significant difference between 30 W and other treatments for 10 min. A possible explanation for this difference in pH values might be related to high CO2 levels inside 90 W and CNT packages. High CO2 accumulation is an indicator of the high respiration and degradation rates of organic acids (Almenar et al., 2007; Holcroft & Kader, 1999; Zhao et al., 2007). These findings showed that 30 W and 60 W ultrasound treatments were effective in maintaining pH of strawberries during storage. 3.3. Total soluble solids Total soluble solids (TSS) play an important role in affecting fruit quality and consumer acceptability. Statistical analyses showed that interactions of factors (including two and three factors) were not significantly important. But main effects of storage time and ultrasound power were statistically significant (Tables 2a and 2b). TSS content of 30 W treatment was statistically different from the CNT and 90 W treatment. Possible explanation for this might be that 90 W treatment distorted and disrupted the cell structures of strawberry and formed microscopic channels which results in water loss (Fernandes, Gallão, & Rodrigues, 2009) (Table 2c).

3.5. Decay incidence Gray mold is a common and serious disease which can cause significant amount of loss during storage, transportation and marketing of strawberries (Zhang et al., 2007). Fig. 2 shows that there has been a marked increase in the number of infected strawberries during storage. No significant differences found between ultrasound treatments. However, there was a significant

Table 4b Effect of different storage times on a* value of strawberry during storage. Storage time (week)/a* value 0 Week

1 Week

2 Weeks

3 Weeks

4 Weeks

36.13  1.33A

33.47  1.75B

32.26  2.72B

30.46  1.85C

29.16  1.77C

AeC

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

Table 4c Effect 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

AeC

Color is an important parameter for determining the quality of fresh products and the quantity of anthocyanins which known as a responsible compound of attractive, red color of strawberry (Rodrigo, Van Loey, & Hendrickx, 2007). Changes in L* values for different treatments during storage are shown in Table 3a. The statistical analyses showed that interactions of factors (including two and three factors) were not significantly important. On the other hand, main effects of storage time and ultrasound power were statistically significant (Tables 3b and 3c). Statistically significance was found between 90 W and 30e60 W treatments. The results of L* values indicated that 30 W and 60 W treatments were effective to preserve the bright color of strawberry when compared with CNT and 90 W. Table 4a shows the changes in a* values for different treatments during storage. Statistical analyses showed that interactions of factors (including two and three factors) were not significantly important. However, main effects of storage time and ultrasound power were statistically significant (Tables 4b and 4c). After one week of storage, a* values of strawberry dropped distinctly, and remained steady in the second and third weeks (Table 4b). It is possible that 90 W treatment had adverse effect on the anthocyanins stability of strawberry due to cavitations including the formation of hydroxyl radicals (Tiwari, Patras, Brunton, Cullen, & O’Donnell, 2010).

25

20

Decay Incidence (%)

3.4. Color

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

15

10

5

0 0

1

2

3

4

5

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

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A

B 6,00 5,75 800

5,50 Adhesiveness (g.s)

Firmness (g)

5,25 600

400

5,00 4,75 4,50 4,25 4,00 3,75 3,50 3,25

200

3,00 0

1

2

3

4

5

0

1

Storage Time (Weeks)

2

3

4

5

Storage Time (Weeks)

C

D 0,55 Cohesiveness (Dimensionless)

Springness (Dimensionless)

0,70

0,65

0,60

0,55

0,50

0,45

0,50 0,45 0,40 0,35 0,30 0,25

0

1

2

3

4

Storage Time (Weeks)

E

0

5

F

1

2

3

4

5

4

5

Storage Time (Weeks)

300

400

Chewiness (g)

Gumminess (g)

250

300

200

150

200 100

100

50 0

1

2

3

4

5

0

1

Storage Time (Weeks)

G

2

3

Storage Time (Weeks)

0,26

Resilience (Dimensionless)

0,24 0,22 0,20 0,18 0,16 0,14 0

1

2

3

4

5

Storage Time (Weeks)

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.

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difference between control and ultrasound treatments. It is possible that ultrasound treatments punctured cell walls and damaged membrane functions of molds (Guerrero, Tognon, & Alzamora, 2005). Our results are in good agreement with Cao et al. (2010) who found that ultrasonic treatment reduced the fruit decay in strawberry. 3.6. Texture profile analysis (TPA) Texture is a main characteristic of strawberry related to the quality. Texture gives comprehensive information about microstructure of foods as well as cell wall, middle lamella and turgor pressure (Fraeye et al., 2010). Firmness, cohesiveness, springiness, gumminess, chewiness and resilience values of strawberry increased while adhesiveness values decreased during storage time in all treatments (Fig. 3). Firmness can be attributed to the physical anatomy of tissue, cell size, shape, cell wall strength and intercellular adhesion (Toivonen & Brummell, 2008). The higher firmness values were obtained with treatment of 30W5M and 30W10M whereas the lower values were obtained with 90W5M and 90W10M (Fig. 3(A)). The observed

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decrease in firmness for 90 W treatments could be attributed to destructive effect of high power ultrasound on stability of cell wall which results in loss of water (Fernandes et al., 2009). The term adhesiveness has come to be used to refer to surface characteristic which related with adhesive and cohesive forces (Rahman & Al-Farsi, 2005). Higher values for 90 W treatment may be due to adverse effect (expansion and contraction) of high acoustic intensity in solid matrix (Fig. 3(B)) (García-Pérez, Cárcel, Benedito, & Mulet, 2007). Springiness can be defined as the rate that deformed food goes back to its undeformed condition (de Huidobro, Miguel, Blazquez, & Onega, 2005). The Fig. 3(C) indicates that springiness values of CNT and 90 W treatments were lower than 30 W and 60 W treatments during storage. It is possible that 90 W treatments destroyed the structural 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 and difficulty degree in breaking down the internal structure (Yang et al., 2007). At the end of the storage, CNT and 90 W treatments have the lower cohesiveness values compared with other treatments (Fig. 3(D)). Possible explanation for this might be that high

Fig. 4. 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 FT-NIR spectra’s at reflectance and transmission modes during storage.

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power ultrasound created the microscopic channels with reducing the diffusion boundary layer (Azoubel, Baima, Amorim, & Oliveira, 2010). The use of term gumminess is related to force required to chew or swallow to food. It was decreased during the storage for all groups (Fig. 3(E)). The observed reduction of gumminess values for CNT and 90 W treatment could be attributed to the high hydrolysis reactions rate and adverse effect of high power ultrasound on the turgor pressure (Del-Valle, Hernandez-Munoz, Guarda, & Galotto, 2005). Chewiness can be defined as the energy for masticating semisolid sample (Huang, Kennedy, Li, Xu, & Xie, 2007). Fig. 3(F) showed that with high power ultrasound (90 W) less energy was needed to masticate the sample. This result may be explained by the fact that high power acoustic energy destroyed the primary cell wall and middle lamella more than that of the 30 W and 60 W treatments. Resilience is the energy for fighting back to its original state (Rahman & Al-Farsi, 2005). The values of 30 W and 60 W treatments decreased slightly whereas the values of CNT and 90 W dropped sharply during storage (Fig. 3(G)). The findings of TPA analysis showed that 30 W and 60 W treatments maintained the TPA parameters better than that of CNT and 90 W treatments. It seems possible that high power ultrasound had destructive effect on cell wall constituents of strawberry. 3.7. Fourier transform near infrared (FT-NIR) spectroscopy evaluation FT-NIR is a novel approach to estimate the quality attributes of food using specific wavelengths between 750 nm and 2500 nm (Chen, Cai, Wan, & Zhao, 2011). It is a rapid, effective and nondestructive 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 and transmission modes of treatments are shown in Fig. 4a and b. The bands around 8454 and 5623 cm1 are caused by the sugars and bands around 10,244 cm1 can be attributed to water content (Di Egidio et al., 2009). At the beginning of the storage, absorption spectrum showed high absorbance for sugar and water content due to freshness quality, as expected. Increased storage time resulted in decrease of absorption bands for all treatments. At the end of the storage, absorption peaks around 8454 cm1 dropped significantly for CNT and 90 W when compared with other treatments. Correlation was found between these results and TSS values. The lowest peaks were observed around 10,244 cm1 for CNT and 90 W treatments due to the high respiration rate and metabolic activity of CNT group and destructive effect of high power ultrasound on cell wall and cellecell adhesion which results with greater loss of water. 4. Conclusions This paper has given an account of and the reasons for the use of ultrasound in the food industry. This study was designed to determine 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 significant difference between treatment times. It was however found that, ultrasound power between 30 W and 60 W could be used to extend shelf life of strawberry. It was observed that the high power ultrasound (90 W or higher) presents detrimental effects on strawberry quality. The empirical findings in this study provide a new understanding of ultrasound power. Finally, this research has

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