Preparation Of Poly(L-lactic Acid)/Chitosan Antibacterial Film By UV Curing And Its Effect On The Preservation Of Chilled Meat

Chilled meat is rich in nutrition and delicious,and is deeply loved by consumers.However,chilled meat is susceptible to microbial infection from production,transportation to sale stage,which is prone to excessive microbial counts,resulting in protein degradation,fat oxidation and quality deterioration.Antibacterial packaging has the function of inhibiting microbial physiological activity and reducing the number of microorganisms,so as to stabilize food quality,delay food spoilage and prolong the shelf life of goods.Therefore,antibacterial packaging is often used to solve the problem of spoilage and deterioration of chilled meat.In this work,firstly,low molecular weight poly（L-lactic acid）（PLLA）and poly（itaconic acid-co-butanediol）（PBI）were synthesized,and then the copolymers were mixed for polycondensation reaction to obtain high molecular weight poly（PLBI）（L-lactic acid co-itaconic acid-co-butanediol）.Secondly,according to the molar ratio（1:0.4,1:0.6,1:0.8,1:1.0）,chitosan（Cs）was grafted with glycidyl methacrylate（GMA）to synthesize chitosan copolymer（Cs-g-GMA）with double bond groups.Finally,the Cs-g-GMA coated PLBI film was laminated by UV irradiation to obtain the PLBI/Cs-g-GMA antibacterial film with an interface bonded by covalent bonds.And it was applied to the storage of chilled beef to assess the indicators during storage and to clarify the effect of antibacterial packaging on chilled beef.The specific research content and results are as follows:（1）The introduction of PBI resulted in a significant increase in the flexibility of PLLA,with the elongation at break of PLBI films reaching 214.3%,and Young’s modulus decreasing to 197 MPa.The DSC test results showed a reduction in T_g of PLBI film,which is a result of the flexibility of the PLLA chain segments being enhanced by the softness of the PBI,which also leads to a reduction in the crystalline properties of PLLA,to get a transparent plastic film material.Cs-g-GMA was grafted onto the surface of the PLBI film after UV irradiation to prepare a covalently bonded cross-linked composite film.The addition of Cs-g-GMA formed a hydrophilic layer on the surface of PLBI,which was easily accessible to microorganisms and improved the microbial bactericidal rate.Escherichia coli,Pseudomonas fluorescens and Staphylococcus aureus were selected as test strains,the results showed that:PLBI/Cs-g-GMA film has antibacterial ability,and the films were ranked as follows:PLBI/Cs-g-GMA_1.0 film>PLBI/Cs-g-GMA_0.8 film>PLBI/Cs-g-GMA_0.6 film>PLBI/Cs-g-GMA_0.4 film.The inhibition rates of Escherichia coli,Pseudomonas fluorescein and Staphylococcus aureus were 49%,63%,74.5%and 83.4%;49%,55%,76%,83%and51.5%,70.7%,81.1%,91.4%;The results of flow cytometry,intracellular material leakage andβ-galactosidase showed that the antibacterial film acted on the cell membrane structure,to inhibited the growth and reproduction of microorganisms by destroying the cell structure.（2）PLBI/Cs-g-GMA_0.6 film and PLBI/Cs-g-GMA_1.0 film were used to store chilled beef at 4℃and to test the quality and microbiology of the chilled beef.The results showed that the values of all indicators during storage were lower than those of the other groups,which reduced the rate of juice loss;stabilized the color and appearance quality;slowed down the rising trend and duration of the p H and TVB-N;and reduced the total number of microbial colonies of the chilled beef.On the 9th day,the TVB-N and the number of colonies in PLBI packaging group reached the standard of rotten meat.The PLBI/Cs-g-GMA_0.6 and PLBI/Cs-g-GMA_1.0 antibacterial packaging group were extended to 12 days and 15 days.And through the analysis of microbial diversity of chilled beef,it can be seen that the number of microorganisms in the antibacterial film group was less than that in the other groups,and there was a significant inhibitory effect on Proteobacteria and Aeromonas.The storage of chilled beef showed that the antibacterial film can effectively inhibit microbial growth,prolong the shelf life,reduce losses and obtain more commodity value.