Accepted Manuscript
Degradation of adenosine triphosphate, water loss and textural changes in frozen common carp (Cyprinus carpio) fillets during storage at different temperatures
Dapeng Li , Na Qin , Longteng Zhang , Qian Li , Witoon Prinyawiwatkul , Yongkang Luo
PII: S0140-7007(18)30447-X
DOI: https://doi.org/10.1016/j.ijrefrig.2018.11.014
Reference: JIJR 4173
To appear in: International Journal of Refrigeration Received date: 1 July 2018
Revised date: 9 November 2018 Accepted date: 13 November 2018
Please cite this article as: Dapeng Li , Na Qin , Longteng Zhang , Qian Li , Witoon Prinyawiwatkul , Yongkang Luo , Degradation of adenosine triphosphate, water loss and textural changes in frozen common carp (Cyprinus carpio) fillets during storage at different temperatures,International Journal of Refrigeration(2018), doi:https://doi.org/10.1016/j.ijrefrig.2018.11.014
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Degradation of adenosine triphosphate, water loss and textural changes in frozen common carp (Cyprinus carpio) fillets during storage at different temperatures
Running title: Changes in IMP of carps during frozen storage
Dapeng Li ac, Na Qin a, Longteng Zhang a, Qian Li a, Witoon Prinyawiwatkul c, Yongkang Luo ab*
a Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, PR China
b Beijing Laboratory for Food Quality and Safety, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, PR China
c School of Nutrition and Food Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA 70803-4200, USA
*Corresponding Author, Tel.: +86-10-62737385; Fax: +86-10-62737385. E-mail:
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Abstract
The quality of frozen aquatic products is directly affected by the changes in water loss and texture, as well as adenosine triphosphate (ATP) degradation, which affects its flavor. In the current study, the drip, cooking and centrifugal losses and texture, as well as the ATP degradation in common carp fillets were compared among four temperatures during frozen storage. The drip, cooking and centrifugal loss, as well as cohesiveness and chewiness at -60 °C storage, showed almost no change. The changes in water loss and texture were similar at -30 and -40 °C storage but these losses were less than those at -20 °C. In addition, the adenosine monophosphate deaminase (AMPD) and acid phosphatase (ACP) of fish during frozen storage were still active. The rate of ATP degradation at -20 °C, which can also be reflected by the changes in K values, was faster than those at -30 and -40 °C. The hypoxanthine ribonucleoside (HxR) and hypoxanthine (Hx) levels were almost constant at -60 °C, while only little changes in the value of ATP and inosine monophosphate (IMP), as well as AMPD and ACP activity, were observed. Overall, ATP degradation still occurred at -20 ~ -40 °C while it was almost inhibited during the -60 °C storage.
Keywords: common carp; frozen storage; quality; ATP degradation; ATP related enzyme.
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1. Introduction
With a harvest of approximately 4M tonnes in 2015 (FAO, 2017), common carp (Cyprinus carpio) has been one of the most important freshwater fish, especially in China. It offers abundant nutrients particularly a significant amount of protein.
However carp is highly perishable due to the high enzyme and microbiological activity. Traditionally, common carp are sold alive, and freezing is not a common treatment. Freezing is still the most effective and widely used method to minimize bacterial growth and enzyme activity for processed fish. Freezing also meets the high demand of ready-to-use, high quality and safe food products required for the changing lifestyle of consumers (Kong et al., 2016). However, protein denaturation, lipid oxidation and hydrolysis still occur during frozen storage, leading to off-odor formation, discoloration and destruction of texture in aquatic products (Benjakul and Bauer, 2000; Benjakul and Sutthipan, 2009). During freezing, there are also changes in the distribution and mobility of the water in the fish tissue (Herrero et al., 2005).
During frozen storage, water transfers to larger spatial domains, and parts of immobilized water changes to free water. Research has been therefore focused on the changes of texture and water during -10 and -20 °C storage, as well as the difference between frozen and refrigeration storage (Barroso et al., 1998; Yin et al., 2014).
However, these studies seldom compared the changes in texture and water distribution of carp during freezing or super-freezing storage.
Changes in protein and fat are very important in fish during storage, which affects for quality of fish. However, adenosine triphosphate (ATP) degradation is also
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an important chemical change in fish that can indicates freshness. In general, ATP degradation is mainly caused by microorganisms and enzymes (Howgate, 2006). It following the degradative sequence of ATP → adenosine diphosphate (ADP) → adenosine monophosphate (AMP) → inosine 5’-monophosphate (IMP) → hypoxanthine riboside (HxR) → hypoxanthine (Hx) (Hong et al., 2017). IMP can provide an umami flavor for the fish. Some scientists believe that the amount of IMP is an indicator of the freshness of fish products (Minami et al., 2011; Ocano-Higuera et al., 2011). IMP generation and hydrolysis in fish are controlled by adenosine monophosphate deaminase (AMPD) and acid phosphatases (ACP), respectively (Li et al., 2016; Li et al., 2017b). Hypoxanthine (Hx) is a bitter substance causing spoilage, making fish is a bitter substance, which also a spoilage substance, that makes fish unpleasant (Hong et al., 2017; Li et al., 2017b). Shiba et al. (2014) and Li et al.
(2017b) investigated the catabolism of ATP in sterile and non-sterile fish fillets during chill storage and found that the conversion of ATP to IMP is mainly autolysis, while bacteria may play prominent roles in the generation of Hx.
Frozen storage for fish species is one of the best methods that limit microbial and enzymatic activity (Makarioslaham and Lee, 1993). Interestingly, some studies reported that the ATP degradation still occurs in aquatic products during frozen storage (Huang et al., 2006; Li et al., 2017a; Wang et al., 2007). Although the range of temperatures in which this occurs is still unknown. There are very few reports about ATP degradation and activity of relevant enzymes (such as AMPD and ACP) during frozen or ultra-low temperature storage (Tolstorebrov et al., 2016).
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The aim of the present study was to compare the changes in texture, water loss and moisture distribution of common carp fillets during frozen and ultra-low temperature storage, as well as the ATP-related compounds ATP, IMP, HxR and Hx, and two relevant enzymes (AMPD and ACP) activity. This study will offer some understanding of the causes of water loss and ATP degradation occurring in frozen-stored carp, which is possibly applicable to other fish species.
2. Materials and methods 2.1 Sample Preparation
Fifty-six fresh common carp with the weight of 1543 ± 82 g and length of 42.2 ± 1.1 cm, were purchased from a local aquatic product wholesale market in Beijing, China, and were transported to the laboratory calmly and alive in foam boxes that contained some water and topped with a perforated thin plastic cover. The research protocol involving fish reported in this study was in accordance with the Guidance on Treating Experimental Animals (2006) developed by China's Ministry of Science &
Technology and Regulations (1988) issued by China State Council. All the fishes were sacrificed by a knock on the head, scaled, gutted, headed and washed. They were cut into fillets (weight: 200 ± 15 g, size: 10 × 10 × 2.5 cm3). From fifty-six fish, 112 fillets were obtained and randomly divided into four groups of 28 fillets each.
Each group was stored at -20, -30, -40 °C in freezers (DW-FL270, Zhongke Meling, Hefei, China) and/or at -60 °C in an ultra-low temperature freezer (DW-86L728J, Haier, Qingdao, China) for 6 months. Each fillet was stored in each polyethylene zip-lock bags (size: 22 × 14 cm2) which were sealed properly. Three samples were
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selected randomly from each group and thawed in a refrigerator at 4 °C for 24 h before analysis every month.
2.2 Drip loss
Drip loss was determined according to Alizadeh et al. (2007) with some modifications. All the fillets were weighed before packing and freezing, and the initial weight was W0. After thawing, the sample was weighed and the weight was Wi. The drip loss was calculated using the following equation:
Drip loss (%) = [(W0-Wi) / W0] × 100 (1) 2.3 Cooking loss
Cooking loss was determined according to Hong et al. (2013) with some modifications. The sample cubes (1.5 × 1.5 × 1 cm3) were cut from the thawed fillets, weighed (Wb), and then placed in zip-lock bags individually. All the bags were cooked by immersing in a water bath at 85 °C for 15 min. After that, sample cubes were taken out from the bag and cooled at room temperature for 5 min. Then each of the cubes was reweighed (Wc). The cooking loss was calculated using the following equation:
Cooking loss (%) = [(Wb - Wc) / Wb] × 100 (2) 2.4 Centrifugal loss
The centrifugal loss was determined according to Shi et al. (2014) with some modifications. 2 g of sample was put into a tube that contained tissue paper to absorb water and centrifuged in a centrifuge (TGL-16A, Changsha, China) at 1760 × g for 10 min at 4 °C. After that, the sample was taken out and weighed. The centrifugal loss
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was calculated using the following equation (Wp was the initial weight of the sample and Wf is the weight of the sample after centrifuging):
Centrifugal loss (%) = [(Wp - Wf) / Wp] × 100 (3) 2.5 Moisture distribution
The moisture distribution was measured using a Niumag Benchtop Pulsed NMR Analyser PQ001 (Suzhou Niumag Analytical Instrument Corporation, Suzhou, China) in a low field nuclear magnetic resonance (LF-NMR) with a resonance frequency of 23.0 MHz according to the method of Bertram et al. (2007) and Shao et al. (2016) with some modifications. Fish cubes of 1.0 × 1.0 × 1.0 cm3 were cut from the fillets and placed into cylindrical glass tubes. The tubes were inserted into the LF-NMR probe one by one. Carr–Purcell–Meiboom–Gill (CPMG) sequence, with a τ-value (time between 90° and 180° pulses) of 120 μs, was used to test the transverse relaxation (T2) at 32.00 °C. T2 data were acquired from 3000 echoes of 8 scan repetitions. MultiExp Inv analysis software, obtained from Niumag Analytical Instrument Corporation was used to analyze the T2 data.
2.6 Texture
The texture parameters of fish including hardness, cohesiveness, and chewiness were carried out by a CT3 texture analyzer (Brookfield, Wis., U.S.A.) following the method of Lu et al. (2015)and Zhang et al. (2017) with some modifications. A sample cube of 1.5 × 1.5 × 1.0 cm3 was cut from the thawed fish. The texture was performed with a 2.0 × 2.0 cm2 TA3/100 square probe, 7 g trigger load, 50% pressed depth, 1 mm/s of test speed and two 5-mm consecutive cycles with 5 s holding time between
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cycles
2.7 ATP-related compounds and K value
The ATP-related compounds including ATP, ADP, AMP, IMP, HxR, and Hx were extracted according to Li et al. (2017b) and were analyzed by high-performance liquid chromatography (HPLC) (Shimadzu, LC-10 ATseries, Japan) equipped with a SPD-10A (V) detector. The separation was run on a COSMOSIL 5C18-PAQ column (4.6mm × 250 mm)(Nacalai Tesque, Inc., Kyoto, Japan) with phosphate buffer (0.05 mol/L, pH 6.8) pumped at 1 mL/min at a temperature of 25 °C. The detection was monitored at 254 nm and compared to standards (Sigma-Aldrich Trading Co., Ltd., Shanghai, China).
The K values were calculated by the following equation:
K value (%) = [(HxR + Hx)/ (ATP + ADP + AMP + IMP + HxR + Hx)] × 100 (4) 2.8 The activity of AMPD and ACP
AMPD and ACP activity was determined using an AMPD and ACP assay kits (Nanjing Jiancheng Bioengineering Institute, Nanjing, China) following the method described by Li et al. (2017b). A sample of 1 g was homogenized with 9 mL cold physiological saline (0.85%) for 30 s and centrifuged at 550 ×g for 10 min. The supernatant was separated for the protein level analysis by the biuret method (Torten and Whitaker, 1964). The enzyme activities were determined following the method of assay kits and expressed as units per milligram of protein (U/mg prot).
2.9 Statistical analysis
All experiments were carried out in triplicate. Statistical analysis was carried out
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using SPSS 20.0 (SPSS Inc., Chicago, USA). All data were subjected to one-way analysis of variance (ANOVA) followed by the Duncan method with a significance level of 5%.
3. Results and discussion
3.1 Changes in drip, cooking and centrifugal loss
Fig. 1(a–c) shows the drip, cooking and centrifugal loss of carp fillets during frozen storage with different temperatures. Generally, drip loss can be attributed to denaturation and aggregation of myofibrillar proteins, leading to the loss of water and proteins during the freezing process and frozen storage (Yin et al., 2014). When frozen meat or aquatic products are thawed, the ice crystals in the muscles melt into water. Some water could not migrate back to the cell andtissue, and carry some frees proteins at the same time, which causes drip loss (Li et al., 2017a). When the fish is stored at -20, -30 and -40 °C, drip loss gradually increased along the entire storage period, which was similarly observed for frozen salmon (Soares et al., 2015). The drip loss of -20 °C sample was significantly higher than that at -30 and -40 °C. This may have been due to more protein denaturation and lipid oxidation occurring during -20 °C storage. This led to more tissue and cell rupture, resulting in more water and some protein loss (Lu et al., 2017; Yin et al., 2014). However, the drip loss almost did not change for six months at -60 °C, which was also significantly lower than those of the other three conditions (Fig. 1(a)). This indicates that ultra-low temperature storage can be better at preventing the drip loss of the fish because it was able to prevent the denaturation of the fish protein.
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Cooking loss of frozen fish is shown in Fig. 1(b). The least cooking loss occurred in fish stored at -60 °C, which showed almost no change from the initial level of 12.72% after 6-months storage. However, cooking loss of -20, -30 and -40 °C samples showed a tendency to rise in the first 4 months and decline during 5-6 months of storage. Cooking loss of sample stored at -30 and -40 °C showed no significant differences, but was significantly lower than that at -20 °C during the first 4 months storage. Interestingly, the similar trend was observed for the centrifugal loss in Fig.
1(c). The denaturation and aggregation of the myofibrillar proteins in fish during frozen storage lead to the decrease of water holding capacity, which causes an increase in cooking and centrifugal loss during the first 4 months of storage. As there was a large amount of water loss during the first 4 months storage, there was less free water in the fillets in the following 2 months storage, leading to decrease in the cooking and centrifugal loss. The results show that -60 °C can better prevent fillet water loss, because super freezing can keep the stability of fish myosin more effectively, hence maintaining the structure of fish muscle (Haard and Simpson, 2000).
3.2 Changes inmoisture distribution
Nowadays, LF-NMR is widely used to determine the distribution of water in meat and fish (Li et al., 2017a). A continuous distribution analysis of T2 relaxation in frozen fish fillets subjected to different temperatures is shown in Fig. 2. Three fractions for water in muscle were classifieddue to different water activity: T2b (0-10 ms), T21 (10-100 ms) and T22 (>100 ms), which represented bound water,
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immobilized water, and free water, respectively (Bertram et al., 2007). All the peaks slowly moved to the right with storage time, and the peak of T22 became bigger with lower temperature and increased storage time, which means the water became more and more active. The main loss of water was immobilized water, which existed between fibrils, myofibrils, and muscle cell membranes in fish (Li et al., 2017a). In this study, although the peaks of T21 were higher with increased storage time, they were narrower at the same time. This may be due to the prolonged frozen storage causing myofibrillar protein denaturation that modified the hydration (Yamashita et al., 2003). For the samples stored at different freezing temperatures, there was no significant difference for T22 at month 2. However, a significant enhancing of T22 area appeared for -20 to -40 °C on month 4. The same was not observed for the -60 °C sample indicating that -60 °C can effectively delay changes of immobilized water into free water, decreasing the water loss during storage. In addition, although almost no change in drip, cooking and centrifugal loss was observed, the area of the peak T22 was larger at the 6th month at -60 °C than that of fresh fish. This suggests that even at -60 °C, protein denaturation and muscle structural changes are progressing slowly during storage,which change the water distribution.
3.3 Changes in texture
The results for the frozen samples for hardness, cohesiveness and chewiness, during six months of storage at -20, -30, -40 and -60 °C can be seen in Table 1. The hardness of the fresh fish was 4238 g, decreasing during the six months storage at -20, -30, and -40 °C. The results were similar to previous research for frozen common carp
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where hardness was observed to decrease over 84 days at -18 °C (Vacha et al., 2013).
This reduction in hardness may be due to ice crystals, formed during frozen storage, destroying the structure of the fish muscle. The hardness of -20 °C samples reduced significantly faster than that of -30 and -40 °C fish. However, no significant difference in hardness was found between -30 and -40 °C samples. Increasing cohesiveness was detected at -20, -30, and -40 °C, which was similar to previous results of European hake (Merluccius merluccius) (Pita-Calvo et al., 2017) and Atlantic mackerel (Scomber scombrus) (Aubourg et al., 2013) during -10 °C storage. In addition, chewinessshowed a tendency of decreasing for the first 4 months and then increasing thereafter at -20, -30 and -40 °C. This may be due to changes in moisture content and the interactions of moisture and protein (Herrero et al., 2005). Interestingly, during -60 °C storage, changes in cohesiveness and chewiness were not obvious, while hardness decreased much less than the other three frozen storage groups. This suggests that -60 °C storage is useful in protecting the fish from moisture loss, protein denaturation, and muscle structure changes, which mutually verified with the previously discussed changes in moisture distribution. (section 3.2).
3.4 Changes in AMPD and ACP activity
Fig. 3 (a) and (b) depict changes in AMPD and ACP activities in common carp during frozen storage, respectively. The initial activity of AMPD was 6.64 U/mg prot.
The AMPD activity of -20, -30 and -40 °C samples peaked in the first month of storage. The results (Fig. 4 and 5) indicated that ATP continued to degrade during frozen storage. Even though ATP is converted to ADP and AMP, the level of ATP in
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the first month was still higher than those in the following 5 months. ATP and ADP could enhance AMPD enzyme activity during freezing (Dieni and Storey, 2008).
However, freezing reduced the sensitivity of AMPD to AMP (Dieni and Storey, 2008).
As AMP continued to accumulate during the first month, more AMPD is needed, resulting in increased AMPD activity during the first month storage. In subsequent months of storage, the AMPD activity of -20, -30 and -40 °C samples decreased. The water loss continued during storage which was reflected by the increasing drip loss (Fig. 1). Parts of the AMPD may have been lost with the water, leading to the AMPD activity decrease.
The activity of AMPD in fish at -20 °C was significantly lower than the other two groups (-30 and -40 °C) at the 2nd and 3rd month. On the other hand, the AMPD activity of carp during -60 °C storage showed a slower descending trend than that at the other three conditions. The level of the AMPD activity at -60 °C was significantly higher than the other three frozen temperatures during 2-4 months storage. This indicated that -60 °C storage could be better in slowing down the reduction of AMPD activity.
Changes of ACP activity in fillets are shown in Fig 3(b). The initial ACP activity was 0.014 U / mg prot. ACP activity decreases at first and then increases during frozen storage at -20, -30 and -40 °C. Fidalgo et al. (2015) also found the same trend of ACP activity in Atlantic horse mackerel (Trachurus trachurus) during -10 °C storage decreasing after 1 month of frozen storage and increasing after 3 months. As the protein denatured, the water loss increased (section 3.1), and parts of ACP may
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have been lost with the water loss. Hence, ACP activity decreased at first, but, as most of the water had been lost (Fig. 1). ACP loss also reduced after 1 month storage.
Rupture of lysosymes and release of the enzymes are likely to be ongoing during storage (Fidalgo et al., 2015)causing ACP activity increase. The activity of ACP in fish stored at -20 ° C decreased significantly faster than that at -30 and -40 °C, reaching the lowest point in the second month (0.0074 U / mg prot) and then slowly rising. The ACP activity at -30 and -40 °C reached the lowest in the 4th month.
However, the activity of ACP in fish fillets stored at -60 ° C showed different changes compared to -20, -30 and -40 °C. It showed a slow descending tendency within 6 months storage. The results show that the lower freezing temperature during storage can inhibit the change of ACP activity to a certain extent.
3.5 Changes in ATP-related compounds and K value
Averages for ATP, IMP, HxR and Hx concentrations in common carp fillets stored at different frozen temperatures are shown in Fig. 4. The initial value of ATP in common carp was 0.71 μmol/g. At the -20, -30 and -40 °C, the ATP level of carp declined rapidly during the first two months and continued to decline slowly during subsequent storage. This may be because that the fish was not completely frozen at the beginning few hours of storage, and a large amount of ATP was degraded rapidly (Li et al., 2017b). As the fish was completely frozen, the rate of ATP reduction slowed down. During the last two months, the ATP levels in fish were very low. Wang et al.
(2007) also found that the ATP degraded quickly in various tissues of Oyster (Crassostrea gigas) during the first 2 weeks of -20 °C storage while Cappeln et al.,
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(1999) obtained a very low ATP after 7 weeks of storage of cod at -39 °C. The value of ATP in samples at -60 °C also declined, which was significantly slower than the other three temperatures. The level of ATP reduced to a low level of 0.41 μmol/g in 1-day storage at 4 °C in our previous reports (Li et al., 2017b). The results indicated that freezing can effectively lower ATP hydrolysis but could not stop it, and -60 °C was more effective than the temperatures above -40 °C to inhibit ATP hydrolysis.
IMP is an important flavor substance of fish. Fig. 4(b) shows that the initial IMP content was 4.06 μmol/g, and increased first during 1 month and then decreased thereafter during -20, -30 and -40 °C storage. The level of IMP also increased during the first 15 days and decreased after that in salmon (Salmo salar) at -18 °C (Fernández-Segovia et al., 2012). There was no significant difference in the first 4 months storage at these three temperatures. However, the level of IMP at -20 °C was significantly lower thanthat of fillets stored at -30 and -40 °C in the last two months storage. IMP concentration in fillets increased slower at -60 °C than the other three conditions. Our previous study reported that ACP activity was significantly associated with IMP degradation (Li et al., 2017b). However, in this study ACP activity reduced slowly at -60 °C, but it was significantly higher than that in the other three groups (Fig. 3b). This result indicates that the ACP potentially lost its effect on controlling the hydrolysis of IMP at -60 °C. There may be other factors that cause IMP to be hydrolyzed in frozen storage, which needs further study.
HxR and Hx are the spoilage products in the process of ATP degradation. The initial value of HxR was 0.39 μmol/g. The HxR level progressively increased during
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six-month storage at -20 °C, reaching 2.76 μmol/g, which was significantly higher than that at -30 and -40 °C (1.34 and 1.42 μmol/g, respectively). Fernández-Segovia et al. (2012) also reported that the level of HxR increased to 4.75 μmol/g in salmon at -18 °C during 15 days storage and then decreased. As the ACP activity in -20 °C group was lower than those at -30 and -40 °C during the first two months storage, ACP may not be the main factor for transformation of IMP to HxR during freezing.
The initial value of Hx was 0.14 µmol/g, fluctuating during the first 4 months storage at -20, -30 and -40 °C, and then increasing to 0.74, 0.57 and 0.56 μmol/g, respectively.
However the values of Hx in these three groups were at a very low level. Interestingly, the HxR and Hx levels were almost unchanged at -60 °C. Freezing is helpful in minimizing bacterial growth and activity (Ben-Gigirey et al., 1998). Li et al. (2017b) and Vilas et al. (2018) reported that bacteria may play prominent roles in the transform of HxR to Hx. Based on our results (Fig. 4), freezing is very effective in inhibiting the hydrolysis of HxR and generation of Hx. The lower the temperature, the more obvious the inhibitory effect.
K value, which is related to the ATP degradation, is widely used to evaluate the freshness of fish. The fish is judged to be fresh if the K value is below 20%, and moderately fresh if between 20% to 50%. Changes in K value of fillets are shown in Fig. 5. The initial K value of common carp was 10.4%, which indicated that the fish was very fresh. The K values of -20 °C group increased significantly faster than the others, reaching 54.4% after six-month storage. Huang et al. (2006) reported that the biotransformation change of nucleotide was not inhibited by frozen storage which the
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K value increased in yellow‐ fin tuna (Thunnus albacares) during 6 months storage at -20 °C. There was no significant difference in the K value between the -30 and -40 °C groups, reaching 23.4% and 22.4% at the 6th month, respectively, which means the fish was almost still fresh. The results explained that freezing at -30 and -40 °C could slow down the ATP degradation more effective than at -20 °C. The least level of K value was occurred at -60 °C, which showed almost no change during the storage.
Considering the changes in the level of ATP, IMP, HxR and Hx, it indicated that -60 °C could almost stop the ATP degradation during the storage.
4. Conclusion
This study compared the changes in water loss, texture, and the degradation of ATP, including the level of ATP, IMP, HxR and Hx, as well as the activity of AMPD and ACP for frozen common carp fillets during -20, -30, -40 and -60 °C storage. The AMPD and ACP of fish during frozen storage were still active. ATP degradation in frozen fish was also still in progress at -20, -30 and -40 °C, and it was faster at -20 °C than those at -30 and -40 °C. Interestingly, the degradation of ATP was nearly terminated at -60 °C. Moreover, the -60 °C storage is better than the other three groups in reducing water loss and maintaining texture. The drip, cooking and centrifugal loss and the changes in texture for the fish at -30 and -40 °C were similar, which was less than that at -20 °C. However, the changes in moisture distribution were almost the same at these three temperatures, which the free water significantly enhanced at the 4th month, 2 months earlier than that at -60 °C. Overall, except the enzyme, whether there are other factors that affect the degradation of ATP in frozen
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storage needs further research.
Acknowledgment
This study was supported by National Natural Science Foundation of China (award no. 31471683) and the earmarked fund for China Agriculture Research System (CARS-45).Dapeng Li want to thank the China Scholarship Council’s support for the work.
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130-137.
0 2 4 6
0 3 6 9 12 15 18
a
Drip loss (%)
Storage Time (month)
-20 C -30 C -40 C -60 C
0 2 4 6
10 12 14 16 18 20 22
b
Cooking loss (%)
Storage Time (month)
-20 C -30 C -40 C -60 C
0 2 4 6
12 14 16 18 20 22 24 26
Centrifugal loss (%)
Storage Time (month)
-20 C -30 C -40 C -60 C
c
Fig. 1. Averages in (a) drip, (b) cooking, and (c) centrifugal loss of common carp fillets during frozen storage at different temperatures. Mean values of three replicates (n = 3); standard deviations are indicated by bars.
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0.01 0.1 1 10 100 1000 10000 0
1000 2000 3000 4000 5000 6000 7000
-60 C 6m -40 C 6m -30 C 6m -20 C 6m -60 C 4m -40 C 4m -30 C 4m -20 C 4m -60 C 2m -40 C 2m -30 C 2m -20 C 2m
Intensity
T2 (ms)
Fresh
T21 T22
T2b
Fig.2 Changes in relaxation time of each relaxation component of common carp fillets during frozen storage at different temperatures and times (m = month).
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0 2 4 6
2 4 6 8 10
AM PD (U /m g pro t)
Storage Time (month)
-20 C -30 C -40 C -60 C
a
0 2 4 6
0.006 0.008 0.010 0.012 0.014 0.016
b
AC P (U/mg pro t)
Storage Time (month)
-20 C -30 C -40 C -60 C
Fig. 3 Averages in (a) AMPD and (b) ACP activities of common carp fillets during frozen storage at different temperatures. Mean values of three replicates (n = 3);
standard deviations are indicated by bars.
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0 2 4 6
0.0 0.2 0.4 0.6 0.8
ATP(mol/g)
Storage Time (month)
-20 C -30 C -40 C -60 C
a 0 2 4 6
2 4 6 8 10 12
b
IMP(mol/g)
Storage Time (month)
-20 C -30 C -40 C -60 C
0 2 4 6
0 1 2 3
c
HxRmol/g)
Storage Time (month)
-20 C -30 C -40 C -60 C
0 2 4 6
0.0 0.2 0.4 0.6 0.8 1.0
d
Hx(mol/g)
Storage Time (month)
-20 C -30 C -40 C -60 C
Fig. 4. Averages in (a) ATP, (b) IMP, (c) HxR and (d) Hx level of common carp fillets during frozen storage at different temperatures. Mean values of three replicates (n = 3);
standard deviations are indicated by bars.
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0 2 4 6
0 20 40 60
K v a lue (%)
Storage Time (month)
-20 C -30 C -40 C -60 C
Fig. 5. Averages in K value of common carp fillets during frozen storage at different temperatures. Mean values of three replicates (n = 3); standard deviations are indicated by bars.
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Table 1
Texture parameters for common carp fillets during 6 months frozen storage.
(mean ± standard deviation (SD))
Texture parameters
Storage time (months)
Storage temperatures
-20 °C -30 °C -40 °C -60 °C
Hardness (g)
0 4238±384A 4238±384A 4238±384A 4238±384A 1 3386±174A 3568±479A 3387±258A NT
2 2162±109A 2780±207B 3263±270C 3867±436D 3 1977±74A 2596±212B 2328±86B NT
4 1710±135A 2283±130B 2197±58B 3428±193C 5 1765±279AB 2017±94BC 2332±303C NT
6 1480±132A 1877±138B 2073±222B 3348±348C Cohesiveness 0 0.22±0.03A 0.22±0.03A 0.22±0.03A 0.22±0.03A
1 0.21±0.03A 0.21±0.04A 0.24±0.06B NT
2 0.23±0.02A 0.21±0.04A 0.23±0.02A 0.23±0.03A 3 0.22±0.04A 0.26±0.03B 0.24±0.03AB NT
4 0.25±0.04B 0.24±0.02B 0.23±0.01B 0.2±0.02A 5 0.26±0.03A 0.25±0.03A 0.26±0.06A NT
6 0.29±0.03C 0.26±0.02B 0.25±0.02B 0.22±0.02A Chewiness
(mJ)
0 20.8±2.9A 20.8±2.9A 20.8±2.9A 20.8±2.9A 1 17.3±3.6A 16.1±4.8A 18.4±4.3A NT
2 13.0±1.0A 16.8±1.2B 17.1±1.9BC 19.6±1.8C 3 10.9±4.0A 16.1±0.4B 15.4±1.4B NT
4 10.6±1.5A 11.9±2.5A 12.8±0.8A 17.8±1.1B 5 14.0±1.6A 13.3±2.0A 17.8±1.9B NT
6 14.7±1.3A 16.0±2.3B 18.5±1.2C 18.9±1.4C
Same capital letters in the same row indicate no significant difference (p > 0.05). NT means the sample was not test that month. Mean values of three replicates (n = 3).
