Preservation Properties Of Sandwich Type KGM/SA/KGM Composite Coatings For Salmon Fillets

The sandwich KGM/SA/KGM composite coatingswere prepared by tape casting with konjac glucan（KGM）and sodium alginate（SA）as the film-forming matrix,epsilon poly lysine hydrochloride（ε-PL）and thyme phenol（Thy）as additives.The coatings were characterized and analyzed by XRD,FT-IR and SEM,and the physicochemical properties,antibacterial properties of the composite preservative coatings were determined.Fresh salmon fillets were used as the object of preservation.The freshness index of salmon fillets during 4℃storage was measured to study the preservation property of composite coatings on salmon fillets,and the effect of composite coatings on protein oxidation of salmon fillets during storage were analyzed.1.The microstructure and mechanical properties of sandwich KGM/SA/KGM composite coatings were improved with the addition ofε-PL and Thy.After addingε-PL and Thy,the thermal decomposition temperature and thermal stability of the coatings are increased due to the interaction between the components.Thy can improve the antibacterial properties of KGM/SA/KGM composite coating,and the inhibition effect on microorganism was significantly improved after the addition ofε-PL.2.The results show that after KGM/SA/KGM composite coating treatment,the total number of bacterial colonies and the volatile base nitrogen value of salmon fillets increased faster,which indicated that KGM and SA promoted the growth of microorganisms in salmon fillets and accelerated the deterioration of the fish.After treated with KGM/SA+ε-PL/KGM composite coating,the microbial growth and lipid oxidation rate of salmon fillets are slowed down.After Thy was added to the composite coatings,the total number of fish colonies and the increasing rate of thiobarbituric acid value are decreased significantly.Among them,KGM/SA+ε-PL/KGM+Thy composite coating has the best preservation properties for fish fillets,extending the shelf life of salmon fillets from the 8d to the 14d.3.The effects of sandwich KGM/SA/KGM composite preservation coatings on protein oxidation and protein secondary structure of salmon fillets were studied.The results show that the inhibition effect of KGM/SA+ε-PL/KGM composite coating on protein oxidation is not significant,and can not inhibit the destruction of protein structure in fish fillets.KGM/SA+Thy/KGM composite coating can delay the oxidative denaturation of fish fillet protein to a certain extent,and stabilize the spatial structure of protein.The decrease rate of carbonyl group content and sulfhydryl group content and Ca²⁺-ATPase activity in the protein was significantly slowed down by the slow release of Thy.The results of fluorescence spectrum and infrared spectrum show that the fresh fish fillets have high fluorescence intensity,and the protein secondary structure is mainlyβ-sheet,with the content of 55.68%.Compared with the untreated sample,the fluorescence intensity and the content ofβ-sheet of the proteinare significantly increased after treated by the composite coating.KGM/SA+ε-PL/KGM+Thy composite coating can delay the denaturation of protein in salmon fillets to the greatest extent.