Prevention of protein oxidation and enhancement of gel properties of silver carp (Hypophthalmichthys molitrix) surimi by addition of protein hydrolysates derived from surimi processing by-products

Surimi processing industry generates huge quantities of underutilized surimi processing by-products (SPB). This study aimed to investigate the potential antioxidant-cryoprotective and gelation-enhancing effects of SPB hydrolysates on silver carp (Hypophthalmichthys molitrix) surimi based on protein oxidation, protein degradation, and gel-forming ability analysis. Results showed that untreated surimi was particularly susceptible to frozen-induced protein degradation and oxidation as well as rapid deterioration in gelation properties. Compared with 4% sucrose-added surimi, partial replacement of sucrose with 2% trypsin- and alcalase-treated SPB hydrolysates effectively delayed the oxidation of cysteine, carbonylation of amino acids, loss of Ca²⁺-ATPase activity, and the destroy of structural integrity of myofibrillar protein in surimi. Moreover, addition of SPB hydrolysates significantly (P < 0.05) increased the initial gelation properties and reduced the loss in gelation and water-holding capacity in surimi with prolonged frozen storage. Therefore, SPB hydrolysates could be used as natural antioxidant-cryoprotectant and gel texture enhancer in freshwater fish surimi.