Effect of Sandwich-Type Konjac Glucan/Sodium Alginate/Konjac Glucan Composite Coatings on Protein Oxidation in Salmon Fillets

In order to expand the application of polysaccharide coatings in the preservation of aquatic products, sandwich-type composite coatings were prepared using konjac glucan (KGM) and sodium alginate (SA) as coating substrates and thymol (Thy) and ε-poly-L-lysine hydrochloride (ε-PL) as antimicrobial agents and their effects on protein oxidation in fresh salmon fillets were studied during storage at 4 ℃. The results showed that the solubility, sulfhydryl content and Ca²⁺-ATPase activity of myofibrillar protein in the composite coating treated fillets increased, and the carbonyl content and surface hydrophobicity of myofibrillar protein (MP) decreased remarkably compared with those treated with sterile water after the same storage period. In addition, the tertiary and secondary structures of myofibrillar protein in the composite coating treated group was more complete. In the late storage period, the protein oxidation indexes of salmon fillets treated with KGM/SA+ε-PL/KGM+Thy composite coating were better than those of the samples treated with KGM/SA+ε-PL/KGM and KGM/SA+Thy/KGM composite coatings after the same storage period. Therefore, in the sandwich-type KGM/SA/KGM composite coating, ε-PL and Thy could act synergistically to delay protein oxidation and denaturation. The results of this study can provide technical guidance for the application of edible coatings in aquatic product preservation.