Effect of previous frozen storage on quality ... - Wiley Online Library

International Journal of Food Science and Technology 2014, 49, 1449–1460

Original article Effect of previous frozen storage on quality changes of grass carp (Ctenopharyngodon idellus) fillets during short-term chilled storage Xiaofei Yin, Yongkang Luo,* Hongbing Fan, Hua Wu & Ligeng Feng College of Food Science and Nutritional Engineering, Beijing Higher Institution Engineering Research Center of Animal Products, China Agricultural University, P. O. Box 112, Beijing 100083, China (Received 17 July 2013; Accepted in revised form 20 October 2013)

Summary

The effect of chilled, frozen and freeze-chilled storage on quality of grass carp fillets and soups was evaluated by sensory score, total aerobic counts and biochemical quality. Fish fillets were stored at 4 °C for 6 days (T1), 40 °C for 12 h and then at 20 °C for 5 days (T2), 40 °C for 12 h and then at 20 °C for 5 days, followed by at 4 °C for 4 days (T3). T1 showed higher sensory score, salt-soluble protein content, better colour and texture qualities than T2 and T3 within 3 days. All fillets kept good quality based on the acceptable limit of sensory score, total volatile basic nitrogen and total aerobic count during storage time. According to the transportation and retail time, chilled storage is appropriate when it is within 3 days. If it extends for 5 days, freeze-chilling treatment keeps better quality, but later chilled fillets should be retailed within 4 days.

Keywords

Ctenopharyngodon idellus, freeze-chilled storage, quality changes, soup free amino acids.

Introduction

Fish is widely consumed all over the world and is considered as an important part of a healthy diet. Fresh fish is highly susceptible to rapid spoilage and has short shelf life, resulting from oxidation of lipids, activities of the fish own enzymes and the metabolic activities of microorganisms (Ashie et al., 1996). Furthermore, for some markets further away from the main fish producers, the relative short shelf life necessitates either expensive air freight, frozen distribution or inclusion of more preservative factors. Although the traffic developed, the time elapsing between the harvesting place and the arrival at destinations sometimes may vary from 3 to 5 days. Therefore, it is necessary to optimise the freshness of fish during transportation and storage. To increase shelf life and reduce the rate of microbial and biochemical degradation, different preservative methods, mainly based on low temperature, have been employed. The most widely used transportation form is cold chain transportation. It includes refrigerated ice storage between 0 and 4 °C, superchilled storage in the range of 1 to 4 °C, by means of slurry ice or in superchilled chambers without ice,

*Correspondent: Fax: +86 010 62737385; e-mails: [email protected]; [email protected]

doi:10.1111/ijfs.12431 © 2013 Institute of Food Science and Technology

and frozen storage at 18 to 40 °C (Gallart-Jornet et al., 2007). The effects of freezing and chilling on food are well documented (Gormley et al., 2002; Robinson et al., 2012; ;Bahmani et al., 2011; Gencß et al., 2013). However, the effect of freeze-chilling on the quality of fish fillets has received relatively less attention. Freeze-chilling is a dual procezss, which involves freezing and frozen storage followed by thawing and chilled storage (O’Leary et al., 2000). Freeze-chilling technology had been studied on raw chicken fillets and potato flake storage (Redmond et al., 2002; Patsias et al., 2008). It offers a number of advantages over both frozen and chilled products: (i) freeze-chilling ensures the arrival of product at distant markets in frozen form, after which the product is thawed prior to retail display as chilled food; (ii) foodstuffs can be prepared in bulk, frozen, and stored at deep freeze temperatures until required; (iii) freeze-chilling can reduce the opportunity of product recalls in that this method enables complete routine microbiological testing before the product is released from the manufacturer (Fagan et al., 2003). Grass carp (Ctenopharyngodon idellus) is one of the main freshwater fish species in China and has a large market demand because of its rapid growth, high yield and low price. As a result of the rapid deterioration, the utilisation of grass carp as a basic raw material presents difficult storage problems. Therefore, investigations on

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Grass carp after previous frozen storage X. Yin et al.

the freshness changes in cold chain circulation are of considerable interest. Muscle and soup of grass carp are popular diets. Fish soup is rich in nutrients and has the function of regulating menstruation, lactogenesis and helping the recovery of puerperants. The aim of this study was to investigate the effect of freeze-chilling, chilling and freezing on quality parameters of grass carp fillets and soup during short-term storage. Samples were subjected to sensory quality, total aerobic counts and some biochemical quality tests. We hope to provide useful information for preservation of fish products during transportation and storage. Materials and methods

Sample preparation

Twenty-four pieces of fresh grass carp were purchased from a Haidian aquatic products wholesale market in Beijing, China, in April 2013. The mean weight and length of fish were 1100 50 g and 43 1 cm, respectively. They were immediately transported to the laboratory alive. These fresh grass carp were killed by blunt force trauma to the head, scaled, gutted, filleted and washed. The amount of fish fillets was forty-eight. After washing, the fillets were allowed to drain for 5 min on a stainless steel wire mesh. The drained fillets were weighed, packed in polyvinyl chloride bags and randomly separated into three groups. T1 (chilled), T2 (frozen) and T3 (freeze-chilled) containing twenty-one, fifteen and twelve fish fillets, respectively. T1 group was stored in refrigerated chambers at 4 °C, covered with a layer of flake ice and kept for up to 6 days. T2 group was frozen at 40 °C for 12 h and then moved to a freezer at 20 °C and kept for up to 5 days. T3 group was frozen at 40 °C for 12 h, stored at 20 °C for up to 5 days followed by chilled storage at 4 °C for up to 4 days, covering with a layer of flake ice. The fresh grass carp was tested with no storage (at day 0). T1 samples were analysed every day for changes in the freshness indices from day 0 to day 6. T2 samples were thawed in a refrigerator at 4 °C for 12 h and then the changes in freshness indices were evaluated every day from day 1 to day 5. After storage at 40 °C for 12 h and then at 20 °C for 5 days, T3 samples were moved to refrigerated chambers at 4 °C and were also taken for analysis every day from day 1 to day 4. Three randomly chosen fillets from each group were analysed at equal intervals. Soup was prepared according to the method of Zhang et al. (2013) with some modifications. Grass fish fillets (200 g) were added to 800 mL water with 4 g NaCl and then cooked at a temperature of 95 1 °C for 2 h. The soup was cooled to room temperature and clarified by sieving through a 0.15mm-mesh sieve. The soup filtrate was obtained, which was used in the following analysis.

International Journal of Food Science and Technology 2014

Sensory analysis

The raw fillet samples were analysed following the methodology recommended by Ojagh et al. (2010) with some modifications. The samples were evaluated by a panel consisting of six rigorously trained assessors from the laboratory staff. The sensory evaluation was based on a five-point scale to determine colour discoloration (5, no discoloration; 1, extreme discoloration and very dim); odour (5, extremely desirable; 1, extremely ammonia odour); muscle morphology (5, extremely compact and complete; 1, very loose); muscle elasticity (5, full of elasticity; 1, very inelastic) of the samples. Shelf life criteria assumed that rejection would occur when the sensory attributes declined below 3.0. The overall sensory score was calculated by summing the mean score awarded for each of the four characteristics of raw fillets for a highest possible score of 20. Every aspect of sensory quality can be evaluated by decimal. Colour analysis

Fillet colour was measured using a fully automatic colorimeter (ADCI-60-C, Beijing Chentaike Instrument Technology Co., Ltd., Beijing, China). The colour of fillet mince from the white muscle was measured after standardising the instrument with white and black tiles provided by the manufacturer. The tristimulus L* a* b* measurement mode was used, with L* representing lightness, a* representing red/green (+a* red, a* green) and b* representing yellow/blue (+b* yellow, b* blue). Instrumental texture analysis

The instrumental analysis of texture was performed by a CT3 texture analyser (Brookfield, USA). Fish cubes (15 9 15 9 15 mm) were taken from the dorsal muscle of every fillet. Analysis was performed by pressing a square probe (TA3/100) on the fillets at a constant speed (1 mm s1). The test conditions involved two consecutive cycles of 30% compression with 5 s between cycles. The results were expressed as hardness, adhesiveness, springiness, cohesiveness, gumminess and chewiness. Total aerobic count analysis

Total aerobic count (TAC) was determined from plate count agar by the spread plate method (AOAC International, 2002) and estimated according to the method of Yao et al. (2011). Determination of total volatile basic nitrogen

The total volatile basic nitrogen (TVB-N) content was determined as described by Hu et al. (2013). The method was based on steam distillation and extraction

© 2013 Institute of Food Science and Technology


of volatile base nitrogen. And the distillate was titrated with standard hydrochloric acid. The results were expressed as mg TVB-N per 100 g muscle. Determination of centrifugal loss and drip loss

Centrifugal loss was determined on minced muscle by low-speed centrifugation as described by Hultmann & Rustad (2002). Samples (2–3 g) of minced muscle were centrifuged at a centrifugal force of 210 g. The weight before and after centrifuge was expressed as Wa and Wb. Centrifugal loss was calculated according to the following equation: Centrifugal loss ð%Þ ¼

Wa Wb 100 Wa

ð1Þ

Fillets were weighed after being drained (Da). After the designated storage period, the fillets were taken from polyvinyl chloride bags and then blotted with a paper towel and reweighed (Db). Drip loss was calculated according to the following equation: Drip loss ð%Þ ¼

Color

Odour

Morphology

Muscle elasticity

Total scores

Storage time (days) 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6

T1

The content of the water-soluble protein (WSP), saltsoluble protein (SSP) and soup protein was determined. Water-soluble protein was extracted according to the method of Tadpitchayangkoon et al. (2010) with some modifications. Two grams of fish mince was

5.00 4.80 4.67 4.33 3.83 3.00 3.33 5.00 4.25 4.50 4.00 3.83 3.50 3.33 5.00 4.50 4.33 4.00 4.07 3.80 3.60 5.00 5.00 4.33 4.33 3.83 3.00 3.50 20.00 18.30 17.43 16.50 15.73 13.30 13.77

T2

A

0.00 0.20Aa 0.29ABa 0.29Ba 0.29Ca 0.28 Da 0.30D 0.00A 0.35ABa 0.87Ba 0.29BCb 0.20BCb 0.50Ca 0.29C 0.00A 0.10Ba 0.29Ca 0.20Cb 0.11CDa 0.16 Da 0.17D 0.00A 0.20Aa 0.29ABa 0.76BCa 0.76Ca 0.20 Da 0.50C 0.00A 0.11Aa 1.04Ba 0.86Ba 0.49Cb 0.23 Da 1.10D

– 4.27 4.27 4.00 3.50 3.93 – – 4.27 4.33 4.33 4.00 4.30 – – 4.67 4.37 4.17 4.50 4.20 – – 3.83 3.67 3.50 3.60 3.37 – – 17.80 17.50 16.80 16.20 16.00 –

ð2Þ

Determination of protein content

Table 1 Sensory score for T1 (chilled), T2 (frozen) and T3 (freeze-chilled) grass carp fillets Parameter

Da Db 100 Da

T3

0.29Ab 0.00Aa 0.10Aab 0.20Bab 0.11Ab

0.29Aa 0.29Aa 0.28Aa 0.20Aa 0.29Ab

0.28Aa 0.29Ba 0.26Ba 0.30Aa 0.32Ba

0.29Ab 0.76Ab 0.50ABb 0.20ABa 0.11Ba

0.58Aa 0.53ABa 0.50ABa 0.14ABa 0.50Bb

– 3.50 3.83 3.83 3.17 – – – 4.40 4.05 3.80 3.65 – – – 4.07 3.83 3.80 3.00 – – – 3.45 3.33 3.40 3.00 – – – 15.45 15.04 14.23 12.82 – –

Means SD (standard deviation) within a row sharing a common letter (lower case) were not significantly different (P > 0.05).

0.50Ac 0.29Ab 0.29Ab 0.28Ab

0.58Aa 0.29Aab 0.25Ab 0.11Ab

0.58Ab 0.29Ab 0.50Ab 0.29Ab

0.46Ab 0.50Ab 0.25Ab 0.23Ab

0.46Ab 1.00Ab 0.51Ab 0.47Bc

Means SD (standard deviation) within a column sharing a common letter (upper case) were not significantly different (P > 0.05) for the same index.



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homogenised with 30 mL cold deionised water using a homogeniser for 1 min. The homogenate was kept in a refrigerator at 4 °C for 30 min to extract WSP and then centrifuged at 11 000 g at 4 °C for 10 min. The supernatant, as a sarcoplasmic protein fraction, was collected, its volume was determined, and the protein concentration was determined by biuret method (Pan et al., 2011). The precipitate was used to extract SSP. Thirty millilitres of chilled 0.6 M NaCl–20 mM Tris–maleate buffer, pH 7.0, was added to the precipitate and then the mixture was homogenised for 1 min. The homogenate was kept in a refrigerator at 4 °C for 1 h to extract SSP and centrifuged at 11 000 g at 4 °C for 10 min. The supernatant was collected and diluted with chilled 0.6 M NaCl–20 mM Tris–maleate buffer (pH 7.0) to reach a volume of 50 mL. The protein concentration was determined by biuret method. Soup protein concentration was determined by biuret method after discarding the upper fat in soup. Table 2 Drip loss, centrifugal loss, TVB-N, and TAC changes for T1 (chilled), T2 (frozen) and T3 (freeze-chilled) grass carp fillets

Parameter Drip loss (%)

Centrifugal loss (%)

TVB-N (mg 100 g1 muscle)

TAC (log10 cfu g1)

Sodium dodecyl sulphate–polyacrylamide gel electrophoresis analysis

Sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) was performed on WSP, SSP and soup protein, which was carried out by the method of Wang et al. (2013) with some modifications. Stacking gel and separating gel were made of 4% (w/v) and 12% (w/v) polyacrylamide for SDS-PAGE analysis of compositions of WSP and soup protein, while 4% and 10% for SDS-PAGE analysis of SSP. Determination of soup free amino acid

About 20 mL of soup with 30 mL of 0.1 M HCl was stirred for 15 min to extract free amino acid (FAA). Then, the mixed liquid was filtered in 100-mL volumetric flask, and the residue was further extracted for FAA and then the filtrate sample was collected and diluted with 0.1 M HCl to reach a volume of 100 mL. The sample (10 mL) was stored at 20 °C for further analysis.

Storage time (days)

T1

0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6

1.15 1.14 1.65 1.45 1.86 2.07 1.90 17.55 18.87 19.42 22.21 16.87 16.45 14.28 8.30 11.45 12.19 11.96 12.44 13.94 12.96 2.29 3.37 3.53 4.10 4.51 5.00 5.86

T2

0.13DE 0.02Ea 0.40BCa 0.13CDa 0.40ABa 0.10Aa 0.20AB 1.69AB 2.23ABa 5.68ABa 2.51Aa 1.52Ba 0.67Ba 0.18B 1.56D 1.73Ca 0.51BCa 0.55BCa 0.91BCb 0.47Aa 0.58AB 0.33E 0.08 Da 0.02 Da 0.06Ca 0.30Ca 0.12Ba 0.15A

– 2.79 3.06 3.38 3.12 3.19 – – 17.93 17.50 18.09 16.97 15.55 – – 10.50 10.85 11.23 11.14 10.70 – – 3.71 4.41 4.01 3.01 3.30 –

T3

0.13Bb 0.27ABb 0.35Aa 0.19ABb 0.29Ab

1.62Aa 1.60Aa 2.90Ab 0.18Ba 0.45Ba

0.23Aa 1.50Aa 0.42Aab 1.34Ab 0.69Ab

0.61Ba 4.41Ab 0.13ABa 3.01Cb 3.30BCb

– 3.18 3.47 3.97 3.68 – – – 18.57 17.90 17.41 17.07 – – – 8.58 9.03 12.43 13.95 – – – 3.82 3.61 4.16 4.80 – –

0.20Cc 0.06BCc 0.23ABb 0.10Ac

1.75Aa 0.40Aa 0.73Ab 0.57Aa

0.84Cb 0.21Cb 0.19Bb 0.82Aa

0.20BCa 0.07Ca 0.08Ba 0.33Aa

Means SD (standard deviation) within a column sharing a common letter (upper case) were not significantly different (P > 0.05) for the same index. Means SD (standard deviation) within a row sharing a common letter (lower case) were not significantly different (P > 0.05).




Table 3 Texture and color changes for T1 (chilled), T2 (frozen) and T3 (freeze-chilled) grass carp fillets Parameter Hardness (g)

Adhesivene (g)

Springiness

Cohesivene

Gumminess

Chewiness (g)

L*

a*

b*

Storage time (days) 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0


T1 829.00 1017.00 1481.50 1057.67 987.00 814.00 974.00 9.67 10.33 11.67 12.00 12.33 13.33 14.33 0.48 0.34 0.31 0.30 0.26 0.27 0.26 0.68 0.52 0.48 0.48 0.48 0.47 0.47 920.00 663.00 677.6 629.6 219.33 378.00 295.00 950.00 455.00 444.67 389.67 243.67 220.33 168.00 44.98 42.74 42.99 42.99 43.32 45.79 49.83 8.99 9.50 9.73 9.67 8.85 8.45 6.77 4.11

T2

C

12.63 5.94Ba 24.04Aa 15.10Ba 23.10Ba 18.39Ca 16.76B 0.58E 0.58DEa 1.15CDa 1.73BCa 0.58BCa 0.58ABa 1.15A 0.03A 0.04Ba 0.01BCa 0.01CDa 0.01DEa 0.01DEa 0.02E 0.04A 0.05Ba 0.05Ba 0.03Ba 0.06Ba 0.02Ba 0.03B 18.99A 8.89Ba 18.50Ba 3.58Ba 16.16Db 13.64Ca 3.64C 4.25A 20.51Ba 8.14Ba 13.01Ca 3.46 Da 18.56Ea 17.56E 0.59BC 0.39Cb 0.94Cb 0.51Cb 0.53BCc 1.40Bb 2.28A 0.59A 0.33Aa 0.81Aa 0.30Aa 1.01Aa 0.70Aa 1.26B 0.39B

– 888.00 743.33 745.00 782.33 694.00 – – 9.67 10.67 11.50 10.67 9.33 – – 0.30 0.29 0.28 0.29 0.25 – – 0.52 0.52 0.49 0.48 0.46 – – 444.00 436.67 390.00 407.67 523.33 – – 270.67 242.50 222.00 241.00 263.67 – – 50.23 47.59 49.48 47.20 48.80 – – 5.00 6.30 4.53 7.63 7.12 – –

T3

19.47Ab 13.47BCb 21.21BCb 9.00Bb 7.78Ca

1.00Ba 1.15ABa 2.12ABa 1.15ABb 1.73Ab

0.03Ab 0.02Ab 0.03Aab 0.02Aab 0.03Aa

0.02Aa 0.02Aa 0.01Aa 0.02Aa 0.02Aa

10.41Ab 17.47Bb 11.78Bb 19.86Ba 18.00Ba

6.81Ab 7.24ABb 4.04Bb 10.60ABa 8.43ABa

1.45Aa 1.51ABa 0.48ABa 0.48Bb 0.85ABa

0.10Cb 0.76Bb 0.20Cc 0.56Aab 0.83Ab

– 743.00 773.00 713.33 675.00 – – – 9.00 9.33 8.50 9.67 – – – 0.28 0.26 0.27 0.24 – – – 0.50 0.49 0.47 0.49 – – – 389.00 368.50 354.00 340.33 – – – 197.00 141.67 165.00 157.67 – – – 48.99 49.62 49.82 49.65 – – – 6.44 6.30 5.24 5.89 – – –

15.02ABc 19.80Ab 12.58ABb 4.24Bc

1.00Aa 1.53Aa 0.71Ab 0.58Ab

0.02Ab 0.01ABb 0.01Ab 0.01Bb

0.02Aa 0.01Aa 0.03ABa 0.02Ba

9.86Ab 9.19Ab 7.04Ab 12.66Aa

1.73Ac 10.02Bc 13.11Bc 3.59Bb

0.16Aa 0.48Aa 0.45Aa 0.36Aa

0.58Ab 0.33Ab 0.54Ab 0.28Ab


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Table 3 (Continued) Parameter

Storage time (days) 1 2 3 4 5 6

T1

T2 3.20 3.36 3.45 4.02 4.28 4.73

0.28Cb 0.19Cb 0.28Cb 0.38Bb 0.41ABb 0.11A

3.50 4.80 5.00 5.35 5.13 –

T3 0.21Bb 0.68Aa 0.40Aa 0.67Aa 0.23Aa

4.83 4.50 5.38 5.03 – –

0.69Aa 0.22Bab 1.21Aa 0.51Aa


The filtrate samples were used to determine FAA composition using the HPLC according to You et al., 2012. Statistical analysis

All the measurements were replicated three times for each group, and mean values standard deviations were reported for each case. The data were subjected to one-way analysis of variance (ANOVA). The least significant difference (LSD) procedure was used to test for difference between means (significance was defined as P < 0.05) using SAS software (SAS Institute Inc., Cary, NC, USA). Results and discussion

Sensory score

Total sensory score of fresh grass carp was 20, which gradually declined in all samples with storage time (Table 1). T2 samples received better colour, odour, morphology and muscle elasticity scores than T1 or T3 at the end of storage. The colour, morphology, muscle elasticity and total sensory score for T1 were higher (P < 0.05) than that for T3 within 4 days. T1 showed higher muscle elasticity score than T2, but no significant changes among colour score and total sensory score for T1 and T2 were observed before 3 days. The difference in sensory score may be resulted from changes in the microstructure of muscle during freeze–thawing. Freezing prior to chilling caused more rapid spoilage of fish during ice storage at 4 °C, compared with fillets that had not been frozen before chilling. Grass carp was considered to be acceptable for human consumption before the sensory scores reached 12 (Zhang et al., 2011). Thus, all treatment groups were still acceptable at the end of storage. These fillets can be consumed by families as edible material. Drip loss and centrifugal loss

The changes in drip loss are shown in Table 2. Drip loss for T1 noticeably increased (P < 0.05) with


storage time. The results agreed with the study of Hong et al. (2013), who found that the drip loss of bighead carp heads during ice storage significantly increased (P < 0.05) as a function of time. T2 and T3 showed no significant increase (P > 0.05) in drip loss with storage time. There was significant difference in drip loss between treatment groups, and the observed values were T3 > T2 > T1 (P < 0.05) within 4 days. It was due to the denaturation and aggregation of the myofibrillar proteins leading to the loss of water-holding capacity during the freezing process and frozen storage (Barroso et al., 1998). Centrifugal loss for T1 showed no significant difference (P > 0.05) before day 4, the same for T2 and T3. However, Hultmann and Rustad (2002) found that centrifugal loss of cod fillets was significantly reduced for cod fillets during iced storage. T2 and T3 had lower centrifugal loss than T1 during 3 days, and it may be due to the large increase in drip loss for T2 and T3. Total volatile basic nitrogen

Changes in TVB-N for grass carp fillets are shown in Table 2. Fresh fillet in TVB-N was 8.30 mg per 100 g. TVB-N of T1 and T3 significantly increased (P < 0.05) as time increased, whereas that of T2 was not. It was due to limited microorganisms during frozen storage. T1 and T3 samples had higher TVB-N values than T2 after day 2, and the same conclusion was found in Fagan et al. (2003). T3 showed higher TVB-N values (P < 0.05) than T1 after day 2, and the larger increase in TVB-N for T3 after day 2 can be explained by freezing treatment prior to chilled storage, which punctured the cells and increased the amount of water in the extracellular space, providing a good culture medium for microorganisms (Lee et al., 2008). According to the European Communities guidelines (The Commission of the European Communities, 1995), the maximum acceptable level of TVB-N was 35 mg per 100 g fish flesh. The TVB-N values for all treatments were within the maximum acceptable level during storage.



Total aerobic count

Table 2 shows the changes in TAC. The initial TAC of grass carp fillets was 2.29 log10 CFU g1. The TAC for T1 and T3 increased remarkably (P < 0.05) with storage time. For low-temperature-limited microbial growth, T2 showed decrease in TAC after day 3. TAC in T1 and T3 shows no significant difference (P > 0.05) during 4 days. According to the proposed limits (7 log10 CFU g1) for fresh fish by ICMSF (1986), all treatments kept relatively good quality during storage. Texture

Textural characteristics are shown in Table 3. Hardness values for T1 increased before day 2 and then noticeably decreased (P < 0.05), and hardness values for T2 and T3 showed no significant decline with storage time (P > 0.05). Adhesiveness values for T1 increased over time, whereas there was no noticeably increase (P > 0.05) for T2 and T3. Decreasing springiness values (P < 0.05) were found in T1, but no significant differences (P > 0.05) were found in T2 and T3 as time increases, and the results were the same as gumminess and chewiness values. Cohesiveness values for all treatment groups showed no significant changes

during 4 days. The similar conclusion was also reported. Martinez et al. (2010) reported as follows that hardness, springiness, gumminess and chewiness values for salmon decreased with frozen storage time. Hultmann & Rustad (2002) reported that hardness values significantly reduced during iced storage, while cohesiveness increased. Different treatments had important effect on textural characteristics. T1 showed higher (P < 0.05) hardness, adhesiveness, springiness and gumminess values than T2 and T3 before day 3. However, there was no noticeable difference between T2 and T3 for the above textural characteristics. During the freezing process, frozen storage and thawing process, fish muscle can undergo a number of changes. Mackie (1993) reported frozen storage to be associated with protein denaturation and water loss. The denaturation and aggregation of the protein maybe resulted in modifications in the functional properties of muscle protein and consequently the loss of water-holding capacity (shown in Table 2), causing the changes in texture. Colour

The surface colour parameters for grass carp fillets are shown in Table 3. It can be noted that initial values of L*, a* and b* were 44.98, 8.99 and 4.11, respectively.

Table 4 WSP, SSP, and soup protein content changes for T1 (chilled), T2 (frozen) and T3 (freeze-chilled) grass carp fillets

Parameter WSP (mg g1 muscle)

SSP (mg g1 muscle)

Soup protein (mg mL1 soup)

Storage time (days)

T1

0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6

50.66 54.08 55.66 56.37 55.47 52.21 51.42 125.90 121.65 122.12 121.00 115.05 112.58 113.10 8.05 8.83 9.36 9.49 9.11 9.35 8.96


T2

1.22C 2.30ABa 0.92Aa 5.30Aa 1.99Aa 1.88BCa 1.07BC 2.00A 9.34ABCa 2.63ABCa 8.31ABa 3.16ABCa 3.00Ca 1.67C 0.05B 0.31ABa 1.13Aa 0.43Aa 0.52Aa 0.63Aa 0.18A

– 53.97 52.15 56.23 50.35 51.60 – – 122.12 124.48 118.11 116.46 116.34 – – 9.33 8.77 9.74 9.00 9.33 –

T3

0.26ABa 4.90BCb 2.31Aa 2.31Cb 1.82BCa

6.35ABa 2.00Aa 4.67BCa 6.02BCa 3.41Cb

0.57Aa 0.11Aa 1.10Aa 0.21Aa 0.79Aa

– 53.86 54.70 51.74 53.25 – – – 116.94 119.45 110.33 107.50 – – – 8.76 8.51 7.87 8.06 – –

0.89Aa 2.37Aab 2.15Ab 3.76Aa


1.94Ab 6.34Ab 4.99Bb 1.50Cb

0.23Aa 0.32ABa 0.35Cb 0.30BCb


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Markerr T1 T1 T2 T3 T1 T2 T3

(a) KDa

T1 T2 T3 T1 T2 T3 T1 T2 T1

97.4 66.2 43.0 31.0 20.1 14.4 0

1

1

1

2

2

2

3

3

3

4

4

4

5

5

6

Storage Ɵme (days) (b) Marker

T1 T1 T2 T3 T1 T2 T3

T1 T2 T3 T1 T2 T3 T1 T2 T1

0 1 1

3

KDa MHC

97.4 66.2

A 43.0 Tr1 Tr2 31.0

Marker KDa 220 170 116 76 53

20.1 1 2

2

2

3 3

4 4

4 5 5

6

Storage Ɵme (days)

(c)

Marker T1 T1 T2 T3 KDa 97.4 66.2 43.0

T1 T2

TT3

T1 T2 T3 T1 T2 T3 T1 T2 T1

31.0 20.1 14.4 0

1

1

1

2

2

2

3

3

3

4

4

Storage Ɵme (days)

Fillets from treatment groups tended to be lighter, less red and more yellow than the fresh fillets with storage time. Oca~ no-Higuera et al. (2011) reported that no distinct increase (P > 0.05) was evident for the L* value of ray fish, while for a* and b*, a significant change was detected (P < 0.05) with respect to iced storage time. T2 and T3 had higher L* and b* and lower a* values than T1 within 4 days. Freezer burn (Lee et al., 2008) and lipid oxidation (Hamre et al., 2003) may be responsible for the colour difference. Protein content

Water-soluble protein and SSP content changes are shown in Table 4. There was no significant difference


4

5

5

6

Figure 1 Sodium dodecyl sulphate–polyacrylamide gel electrophoresis analysis of water-soluble protein (WSP), salt-soluble protein (SSP) and soup protein for T1 (chilled), T2 (frozen) and T3 (freeze-chilled) grass carp fillets. (a) WSP, (b) SSP and (c): soup protein; MHC, myosin heavy chain; A, actin; Tr1, troponin; Tr2, tropomyosin.

(P > 0.05) in WSP content for all the treatments with storage time. However, SSP content of fillets decreased (P < 0.05) as time increased from an initial value of 125.90–113.10, 116.34 and 107.50 mg g1 for T1, T2 and T3, respectively. Munasinghe et al. (2005) noted that SSP of minced yellowtail stored at 4 °C decreased from 123.93 to 119.40 mg g1 tissue in 10 days of storage. Thus, there were more changes in the electrophoretic profiles from myofibrillar fraction than in the sarcoplasmic fraction, as a result of the myofibrillar fraction being most susceptible. Decreasing protein content may be due to autolytic deterioration associated with actions of endogenous enzymes. Different treatments had no noticeable effect on WSP, but T1 and T2 had higher (P < 0.05) SSP con-



Table 5 Concentration (mg/100 mL soup) changes of free amino acid for T1 (chilled), T2 (frozen) and T3 (freeze-chilled) grass carp soup T1 Treatment Time(days) Asp Glu Gly Ala Phe Thr Met Val Ile Leu Lys Tyr Ser His Arg Pro Cys ΣUTAA ΣEAA ΣFAA

0

1

6.68 6.24 9.92 11.75 0.71 4.77 0.79 0.95 1.04 1.39 1.52 1.32 0.46 47.36 57.38 35.19 9.87 35.29 11.82 199.67

e

0.87 0.31f 2.21e 1.07a 0.08a 1.83d 0.01c 0.02b 0.03c 0.04d 0.06f 0.24d 0.04e 5.37ab 4.31bcd 2.91 fg 0.32c 1.87 g 0.83def 2.13def

2

9.08 12.33 16.26 12.29 0.62 6.72 0.86 1.13 1.03 1.24 1.47 1.52 0.92 50.38 57.72 43.62 8.17 50.61 12.99 232.53

ab

0.25 0.34c 0.58b 0.41a 0.03b 0.36b 0.044c 0.21a 0.02c 0.03ef 0.11f 0.08b 0.11bc 1.80a 1.67bc 4.70de 0.01d 1.12a 0.55 cd 4.23a

3

9.65 12.31 16.66 11.09 0.45 6.90 1.03 1.42 0.99 1.19 2.17 1.49 0.96 47.65 66.32 46.22 6.32 50.16 14.14 236.79

a

0.58 1.19c 0.10b 0.34a 0.03d 0.54b 0.09b 0.07a 0.15c 0.01f 0.03b 0.01b 0.06b 0.37ab 0.60a 2.63 cd 0.44e 2.18a 0.56a 5.35a

4

9.01 7.71 14.96 8.09 0.45 6.10 0.57 0.44 1.44 1.44 1.87 1.14 0.82 40.81 53.87 49.38 3.16 34.19 12.17 195.59

abc

0.03 0.42e 0.50bc 0.34b 0.03d 0.39bc 0.02ef 0.02d 0.02b 0.03 cd 0.21c 0.04e 0.03 cd 0.01f 2.31ef 1.03b 0.03 g 1.02 g 0.57ef 4.30ef

5

9.76 6.64 15.19 5.02 0.50 4.52 0.63 0.73 1.47 1.41 1.74 1.16 0.77 40.19 55.03 43.42 4.71 39.01 11.00 186.15

a

0.74 1.20ef 0.89bc 0.53c 0.01bc 0.28d 0.09ed 0.06c 0.06b 0.11d 0.16cd 0.05e 0.08d 1.74f 2.96de 2.94de 0.14f 0.10 fg 0.39ef 2.61 g

6

9.63 5.88 15.03 5.74 0.52 6.14 0.64 1.04 1.67 1.67 1.06 1.36 0.71 36.71 57.26 45.79 6.69 36.81 12.75 197.55

a

0.47 0.27f 0.42bc 0.15c 0.02bc 0.58b 0.06d 0.05ab 0.01a 0.05a 0.05g 0.04d 0.02d 2.03g 1.36bcd 1.36cde 0.19e 1.07 g 0.39def 4.50de

9.90 6.91 17.19 4.40 0.53 6.39 0.80 0.88 1.71 1.68 1.21 1.41 0.82 39.48 54.35 53.54 5.13 40.01 13.19 202.77

1.70a 0.16f 0.68a 0.48d 0.03bc 0.92b 0.02c 0.15c 0.05a 0.08a 0.25g 0.05bcd 0.05cd 0.85bcde 2.03def 0.60a 0.29f 0.09ef 1.20bcd 6.25bc

T2 1 Asp Glu Gly Ala Phe Thr Met Val Ile Leu Lys Tyr Ser His Arg Pro Cys ΣUTAA ΣEAA ΣFAA

7.87 10.69 15.16 5.40 0.59 3.00 0.52 0.28 0.82 1.10 1.55 1.32 0.55 44.21 49.57 46.06 7.83 39.70 7.86 196.52

2

0.15 cd 0.46d 0.40bc 0.24c 0.08bc 0.05e 0.01f 0.01e 0.03e 0.04f 0.07f 0.04d 0.04e 1.19bc 0.49f 0.92 cd 0.27d 0.47ef 0.13 g 2.88ef

7.42 9.94 14.24 8.84 0.64 2.41 0.64 0.40 0.92 1.25 2.34 1.35 0.72 46.81 51.91 48.67 7.78 41.09 8.60 206.29

3

0.52d 1.16d 0.12d 0.12b 0.04b 0.07e 0.01d 0.01d 0.02d 0.01e 0.03a 0.02d 0.01d 0.31b 0.29f 0.62bc 0.11d 1.85def 0.06 g 2.54bc

6.62 10.11 13.57 5.92 0.71 3.09 0.53 0.31 0.92 1.26 1.38 1.38 0.75 41.13 47.19 51.20 6.44 36.93 8.20 191.30

4

0.04e 0.17d 0.07d 0.95c 0.04a 0.01e 0.02f 0.01de 0.01d 0.01e 0.13f 0.04 cd 0.01d 0.30def 0.39 g 0.91ab 0.16e 0.02g 0.07g 2.13f

5

8.10 13.84 14.98 6.99 0.72 7.89 1.02 0.34 1.14 1.31 2.02 1.46 1.15 43.07 56.33 36.96 9.45 44.63 8.43 206.77

0.77bcd 1.00ab 0.32 cd 0.77bc 0.02a 0.03a 0.03b 0.01de 0.03c 0.03e 0.02bc 0.04bc 0.07a 2.07c 2.39cde 1.64f 0.51c 2.71bc 0.03g 7.93bc

7.81 12.79 14.68 8.59 0.66 6.37 1.13 0.36 1.17 1.26 1.35 1.44 0.89 43.78 58.06 36.28 9.51 44.56 12.30 204.35

1.07d 0.50bc 0.35d 1.11b 0.03b 0.61b 0.03a 0.03d 0.04c 0.03e 0.17 g 0.02bc 0.15b 1.45c 1.49bc 2.56f 0.30c 1.30bc 0.71d 2.60bc

T3 1 Asp Glu Gly Ala Phe Thr Met

2 7.87 13.70 14.60 4.50 0.85 3.00 N.D.

d

0.15 0.17bc 0.80 cd 0.27d 0.04a 0.055e


3 8.30 13.47 14.87 6.34 0.77 3.84 N.D.

bcd

0.73 0.73bc 0.67bc 0.30c 0.02a 0.30e

4 7.98 13.00 15.67 4.63 0.72 3.68 N.D.

bcd

0.37 0.77bc 0.68bc 0.20d 0.05a 0.07e

8.13 14.27 18.06 3.75 0.78 5.27 N.D.

1.05bcd 1.00a 1.65a 0.14e 0.05a 0.28c


1457

1458


Table 5 (Continued) T3 1 Val Ile Leu Lys Tyr Ser His Arg Pro Cys ΣUTAA ΣEAA ΣFAA

0.36 1.02 1.31 1.88 1.44 0.58 44.51 60.31 43.07 10.63 41.43 6.96 208.08

2

d

0.01 0.03 cd 0.04e 0.11c 0.11bc 0.03e 1.45c 1.16a 0.92de 0.27b 0.83def 0.29 h 5.49b

0.31 1.08 1.59 1.61 1.69 1.14 44.69 49.29 32.72 10.74 43.75 9.22 188.32

3

de

0.04 0.09 cd 0.99b 0.04 cd 0.07a 0.03a 1.90c 2.32 g 0.58 g 0.51b 1.67bcd 0.35ef 0.47g

0.22 1.03 1.49 1.43 1.51 1.03 39.10 52.32 31.71 11.76 42.76 8.56 188.32

4

f

0.01 0.06cd 0.11c 0.01ef 0.07b 0.06ab 1.60f 2.24f 2.04g 0.50a 1.70cde 0.13 g 0.59g

0.25 1.21 1.68 1.23 1.70 0.94 41.17 53.96 35.09 11.12 46.97 10.42 195.22

0.06e 0.10b 0.02a 0.01g 0.03a 0.10bc 3.07ef 2.08ef 1.07fg 0.96ab 1.99b 0.12e 5.48f

a–hMeans SD (standard deviation) with in a row sharing a common letter were not significantly different (P > 0.05). UTAA, umami-taste amino acids; EAA, essential amino acids; AA, amino acids.

tent than T3. SDS-PAGE analysis of SSP for T3 showed that bonds (molecular weight > 220 kDa) increased and lightened, and some bonds at 220– 76 kDa also lightened, compared with T1 and T2. It revealed the formation of polymerisation with covalent cross-linking and degradation of protein during freezing and thawing process. Thus, decrease in the SSP was due to the progressive denaturation of myofibrillar proteins when fillets suffered from freezing and thawing process. A characteristic distribution of isoforms of various myofibrillar muscle proteins also caused the decrease in protein content (Jasra et al., 2001). Soup protein changes are shown in Table 4. There was no significant difference (P > 0.05) in soup protein with storage time for T1 and T2,but soup protein for T3 remarkably declined at day 3 and day 4. Soup protein slightly increased sometimes, and it had a close relationship with the control of temperature and time when cooking. Soup protein content for T3 was lower than that for T1 and T2 during 4 days, and it may be due to the decrease in muscle protein content (shown in Table 4). SDS-PAGE analysis of soup protein is shown in Fig. 1. SDS-PAGE patterns of soup protein showed that the numbers or strength of bonds had no remarkable difference (P > 0.05) with storage time for all the treatments. About two major protein bonds with molecular weight of 40 kDa and