| In this paper, the grass carp of different weights (1000±100g?1500±150g?2000± 200g) was selected as research object. Further study wass aimed at investigating the surimi characteristics and the impacts of weight on the processing surimi quality, and the indexes were as follows:the pH change after slaughtered, stiffness index, moisture content, Ca2+-ATPase activity, total sulfhydryl, activity of cathepsin B and L, gel strength, and so on. Subsequently the grass carp surimi was added cryoprotectant (cryoprotectants sorbitol, composite phosphate and trehalose). the single-factor experiment and the orthogonal test was performed, the salt-soluble protein, total sulfhydryl and carbonyl were detected to analyze the effect of these three cryoprotectants on grass carp surimi during frozen storage, and a high efficient trehalose-based frozen surimi compound cryoprotectant was obtained.1. The impacts of body weight on the surimi characteristics and the processing surimi qualityDuring cold storage (-4??0-84h), the pH value of all the group tested was increasing after decreasing firstly, along with the increasing of freezing time. And the changing range was 7.24-6.94-7.06 (1000±100g),7.12-6.80-7.06 (1500±150g), and 6.76-6.67-6.74 (2000±200g) respectively. Moreover, it took 60 h,60 h, and 36 h to reach the lowest pH value respectively. The stiffness index increased firstly to the maximum value and then decreased during cold storage (-4?,0h?48h). The stiffness index of 1000±100g group reached the maximum (81.87%) at 6h, and it lasted for 9h; the stiffness index of 2000±200g group reached the maximum (86.84%) at 24h, and it lasted for 33h; while the data of 1500±150g group was in the middle (9h,74.31%,21h).The flesh rate of 1500±150g group and 2000±200g group were 47.08% and 47.28% respectively, and which was extremely higher (p<0.01) than 1000±100g group (46.40%). However, the moisture content of 2000±200g group (78.45%) was significantly lower (0.01<p<0.05) than 1000±100g group (79.90%) and 1500±150g group (79.44%).The salt-soluble protein content of these three groups was not significant (p>0.05). The total sulfhydryl content of 1500±150g group before rinsing was significantly higher (0.01<p<0.05) than 1000±100g group and not significant (p>0.05) with 2000±200g group. After rinsing, the total sulfhydryl content of 1500±150g group and 2000±200g group were significantly higher (p<0.01) than 1000±100g group. Before and after rinsing, other index of 2000±200g group was significantly or extremely significantly higher (0.01<p<0.05 or p<0.01) than 1000±100g group and 1500±150g group.The results of texture indicated that the hardness, cohesiveness, and resilience was no significant difference (p>0.05) among the three groups. The elasticity of 1500±150g group and 2000±200g group were significantly higher (0.01<p<0.05) than 1000±100g group. While the gumminess and chewiness of 2000±200g group were significantly higher (0.01<p<0.05) than 1000±100g and 1500±150g group.Based on the analysis above, we draw a conclusion that the 1500±150g group and 2000±200g group are better in surimi quality than 1000±100g group, thus the grass carp with 1500±150g-2000±200g body weightwass more suitable for producing frozen surimi or surimi products as raw material.2. The optimizing of the cryoprotectants in grass carp surimi during frozen storageThe grass carp with 1500±150g-2000±200g body weight was chose as raw material for producing surimi. Different concentration cryoprotectants (0%,1%,2%,3%,4%,5% of sorbitol,0%,0.1%,0.2%,0.3%,0.4%,0.5% compound phosphate,0%,2%,4%,6%, 8%,10% trehalose) was added to grass carp surimi respectively, and single-factor test was carried out. After the treated surimi was frozen at -20? for 0,2,4,6,8,10,12 weeks, the salt-soluble protein, total sulfhydryl and carbonyl were measured, it was found that the sorbitol, composite phosphate and trehalos of different concentratione could delay the declining of salt-soluble protein content and total sulfhydryl content, and the increasing of carbonyl content for grass carp surimi to varying degrees during frozen storage. Based on the analysis, we could conclude that 1%,2%,3% of sorbitol,0.3%,0.4%,0.5% of compound phosphate, and 4%,6%,8% trehalose were better in antifreeze effect.On the basis of single-factor test,L9(33) orthogonal experiment was conducted, the results showed that the optimum complex combination of cryoprotectant was 2% sorbitol, 0.4% composite phosphate,8% trehalose.Subsequently, to verify the effect of optimum compound cryoprotectant, the frozen surimi without cryoprotectant was set as a control, the surimi with optimum compound cryoprotectant was set as an experimental group. The gel strength was detected and ultrastructure was observed by scanning electron microscopy. The results showed that the gel strength of the experimental group (302.69g.cm) was extremely significantly higher (p<0.01) than the control group (169.08g.cm). The experimental group had compact, less hollow structure, while the structure of control group was looser, and presented more and larger holes.Finally the surimi products (fish cake) were made of frozen surimi which added the optimal complex cryoprotectant, and excellent antifreeze effect was obtained. Thus we concluded that the optimal complex cryoprotectant could maintain the quality of grass carp surimi and its products during frozen storage to a certain extent. |
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