Study On Antibacterial Effect Of Non-migratory Active Packaging And Its Application In Preservation Of Large Yellow Croaker Fillets

Large yellow croaker has become one of the important mariculture fish in China because of its good taste and high nutritional value.With the development of online sales models and cold-chain logistics,more and more aquatic products are being pre-packaged and processed for sale in the form of fillets and cubes.The process of prepackaging and removing offal and gills rich in decaying microorganisms and enzymes is also thought to improve the convenience of fish diets.Large yellow croaker faces the threat of microbial contamination in the process of pre-packaging and processing,so it is necessary to find suitable preservation strategies for pre-treated large yellow croaker.In this paper,polylactic acid(PLA)base film was prepared by high temperature melting extrusion,and then the surface of PLA base film was activated to obtain a dense layer of COOH.Further,the amino group of chitosan(CS)was covalently connected to the surface of PLA film treated by plasma using biological coupling agent,and the grafted non-migration active packaging material was prepared.In this paper,the basic properties of CS-g-PLA film were first characterized,and its antibacterial activity and action mechanism against Staphylococcus aureus were further studied.Finally,the grafted thin film was applied to the preservation of large yellow croak fillets.It lays a foundation for revealing the bacteriostatic mechanism of grafted packaging film and provides a new way for further application of grafted packaging film in production.The main conclusions are:1.The successful preparation of grafted active packaging(CS-g-PLA films)was confirmed by surface carboxylic acid content,surface antibacterial agent content,infrared spectrum,and electron microscopy.Firstly,the standard curve was drawn by ultraviolet spectrophotometer,and the carboxyl group content on the surface of PLA film and grafted film after plasma treatment and the fixed antibacterial agent content on the surface of PLA film and grafted film were obtained.Finally,the results of the permeability test show that the grafting film has significantly enhanced the barrier effect(P < 0.05).2.The antibacterial effect of CS-g-PLA four functional packaging films on S.aureus was studied in this study.The growth of S.aureus on the four grafted films was inhibited by the film inhibition test.The minimum inhibitory concentration(MIC)of CS1-g-PLA for S.aureus was 2.5 mg/m L,and the MIC of CS2-g-PLA,CS3-g-PLA,and CS4-g-PLA films for S.aureus was 1.25 mg/m L.The bacteriostatic effect of the grafted films on S.aureus is complex.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)have confirmed the physical damage,obvious morphological changes,and leakage of intracellular components in the cells treated with the grafted films.Cell permeability test showed that the integrity of bacterial cell membrane was damaged and the conductivity of bacterial culture medium increased.The results of malic dehydrogenase(MDH)enzyme activity showed that the grafted films could affect the complete respiration and metabolism process of bacteria,resulting in the death of bacteria.Gel electrophoresis showed that the grafted film did not affect on S.aureus genomic DNA.3.Large yellow croaker fillets are stored at 4 °C for 13 d.During storage,the comprehensive preservation index of large yellow croaker fillets is determined.The comprehensive results show that: Volatile base nitrogen(TVB-N),thiobarbiturate(TBARS),and the total number of colonies(TVC)showed an increasing trend.CS-gPLA film had no positive effect on the lipid oxidation of large yellow crook fillets.However,the TVC and TVBN values of the CS-g-PLA group were significantly lower than those of the PLA group(P < 0.05).The shelf life of large yellow croaker fillets packed with PLA film was 6 d.Compared with the control,CS-g-PLA film could prolong the shelf life of large yellow croaker fillets for 2～5 d.