Cryoprotective Effects of Protein Hydrolysates Prepared from By-Products of Silver Carp (Hypophthalmichthys Molitrix) on Freeze-Thawed Surimi

The cryoprotective effects of different amounts of protein hydrolysates prepared from by-products of silver carp using Protamex and Alcalase on surimi that were subjected to six freeze-thaw cycles were investigated. Commercial cryoprotectant (8% w/w 1:1 sucrose-sorbitol blend, SuSo) and control (without cryoprotectant) groups were used for comparison. After six freeze-thaw cycles, the lowest actomyosin extractability, Ca2+-ATPase activity and total sulfhydryl content, along with the highest surface hydrophobicity of actomyosin, were observed in the control group (P < 0.05). On the contrary, the group with addition of 2 g of hydrolysate prepared by Protamex hydrolysis (PH-2) displayed the highest actomyosin extractability, Ca2+-ATPase activity and correspondingly, lowest surface hydrophobicity of actomyosin (P < 0.05). Total sulfhydryl content of actomyosin and textural properties of heat-set surimi gels were similar between samples with PH-2 and those with SuSo (P > 0.05). Differences in molecular weight distribution, total and free amino acid compositions between the hydrolysates prepared by Protamex and Alcalase hydrolysis were possible reasons attributing to their variable cryoprotective effects on freeze-thawed surimi. Results from this study clearly support that hydrolysate prepared by Protamex hydrolysis at an appropriate amount could serve as an effective cryoprotectant without increasing the sweetness of surimi products. Furthermore, our findings suggest that the hydrolysates follow a different cryoprotection mechanism compared to SuSo (sucrose-sorbitol blend).