To address the challenges of preventing oxidation and cryoprotection of unwashed surimi during storage, dual-functional peptides were prepared via enzymatic hydrolysis of surimi processing by-products, and their cryoprotective and antioxidant activities were evaluated as well as their influence on protein denaturation, lipid oxidation, gel properties, water migration and ice crystal formation in unwashed surimi during multiple freeze-thaw cycles. The results showed that the prepared bifunctional peptides possessed a thermal hysteresis activity of 0.84 ℃ and increased the survival rate of frozen-thawed yeasts to 74.4%, and they also had good 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (69.0%) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging activity (48.4%). Compared with the control group, the decrease in myofibrillar protein content in unwashed surimi incorporated with bifunctional peptides was reduced by 5%, and the retention rate of Ca²⁺-ATPase activity was increased by 11%, and the increase in thiobarbituric acid reactive substances (TBARS) value was decreased by 25%. The increase in protein carbonyl content and the decrease in gel-forming ability were 65% and 75% of those in the control group, respectively. Meanwhile, the freeze-thaw loss, moisture state transition and ice crystal size of surimi gel with the addition of bifunctional peptides were visibly lower than those in the control group after six freeze-thaw cycles. Therefore, the bifunctional peptides can effectively inhibit oxidative deterioration, protein denaturation, water migration and ice crystal growth during the freeze-thaw process of unwashed surimi, thus enhancing its freeze-thaw stability. These findings contribute to the development of multifunctional improvers for surimi using its by-products and provide a new idea to improve the poor storage stability of unwashed surimi.

To explore the effect of a chitosan-based preservative solution (10 mg/mL chitosan + 5 mg/mL tea polyphenol + 2000 U/mL lysozyme) on the change in the muscle proteome of grass carp during cold storage, differential proteomic analysis of fresh fish and nine-day-stored fish with or without (control) preservative treatment was conducted by two-dimensional electrophoresis-mass spectrometry (2DE-MS). The results showed that the 2DE map of the preservativetreated group was not obviously different from that of the fresh group, except for a decrease in the abundance of fast troponin T and an increase in the abundance of slow troponin T and adenylate kinase isoenzyme. However, the 2DE profile of the control group differed greatly from that of the fresh group in both the number and signal intensity of protein spots. Further analysis showed that the abundance of fast troponin T, tropomodulin 4, synaptopodin 2 and pyruvate kinase type M were down-regulated, while the abundance of myosin heavy chain, myosin light chain 1, α-actin, α-tropomyosin and intermediate light meromyosin were up-regulated. Moreover, compared with the preservative-treated group, the abundance of three troponins T were decreased, while the abundance of myosin heavy chain, intermediate light meromyosin, α-actin, α-tropomyosin and creatine kinase M-type were increased in the control group, suggesting that creatine kinase could serve as an indicator for evaluating grass carp muscle spoilage. This study demonstrates that the chitosan-based composite preservative can maintain the stability of grass carp muscle protein during cold storage.