Atlantic salmon skin gelatin hydrolysate: Antioxidant activity and functional role as a cryoprotectant in freeze-thawed surimi.

Protein denaturation and lipid oxidation during frozen storage negatively affect the quality and consumer acceptance of fish products, underscoring the need for natural additives with both antioxidative and cryoprotective functions. This study presents the first comprehensive evaluation of antioxidant and cryoprotective activities of Atlantic salmon (Salmo salar) skin gelatin hydrolysate (ASGH), produced via a two-step enzymatic process using Alcalase and papain. Sequential hydrolysis generates low-molecular-weight peptides with enhanced radical scavenging and protein-stabilizing properties, strengthening both antioxidant and cryoprotective functionalities. Antioxidant properties were assessed at ASGH concentrations of 1–5 mg/mL. Increasing concentrations enhanced DPPH, ABTS and hydroxyl radical scavenging activities, ferric reducing antioxidant power, and ferrous ion chelation ability, indicating strong antioxidant potential. These mechanisms help suppress oxidative denaturation of myofibrillar proteins, thereby mechanistically supporting its cryoprotective effects. For cryoprotective evaluation, ASGH was incorporated into threadfin bream surimi at 4%, 6%, and 8% (w/ w), followed by three and six freeze-thaw cycles. A 1:1 sucrose/sorbitol blend (8% w/w) and control (without cryoprotectant) groups were used for comparison. ASGH showed dose-dependent mitigation of physicochemical deterioration in natural actomyosin, with higher Ca²⁺-ATPase activity, greater sulfhydryl content, and reduced disulfide bonds relative to the control. Surimi with 4% ASGH showed the greatest textural stability, with breaking force and deformation values reaching 100.33% and 86.97%, respectively, relative to control. These findings demonstrate that ASGH possesses potent antioxidant activity and functions effectively as a natural cryoprotectant, supporting its potential as a clean-label alternative that links antioxidative action with protein stabilization during freeze-thaw abuse.