Preparation Of Poly(l-lactic Acid)/Tannic Acid Antibacterial Films And Its Application In Fresh-keeping Of Chilled Fresh Meat

Cold fresh pork tastes good and has high nutritional value and quality,so it is deeply loved by consumers.However,corruption and oxidation are easy to occur in the process of transportation,processing and sales after slaughter.Therefore,how to ensure the quality and safety of cold fresh pork and extend its shelf life has become an urgent problem to be solved.In this thesis,firstly,poly(itaconic acid-co-butanediol)(PBI)and low molecular weight poly(L-lactic acid)(OLLA)were synthesized,and they were mixed for polycondensation to obtain poly(L-lactic acid-co-itaconic acid-co-butanediol)(PLBI).Secondly,a photoactive tannic acid(pTA)with double bonds was prepared by the ring-opening reaction of tannic acid(TA)and glycidyl methacrylate(GMA).Finally,a series of antibacterial PLBI-pTA films were prepared by grafting on the surface under ultraviolet irradiation,and chemical structure,thermal properties,mechanical properties,hydrophilicity,hydrophobicity,migration quantity and antibacterial and antioxidative properties in vitro of the films were tested.The films were applied to the packaging of chilled fresh pork to evaluate its preservation effect,and the changes of microbial diversity in fresh pork and pork samples of each treatment group at the end of storage were compared and analyzed.The results showed that after grafting modification of pTA,the elongation at break of PLBI-pTA films increased to 328%.Because there were a lot of phenolic hydroxyl groups on the surface of the grafted films,the water contact angle was significantly reduced and the hydrophilicity of the films surface was increased.The total migration in different food simulants and the consumption of potassium permanganate are lower than the migration limit of food contact materials set by the national standard.In addition,the bactericidal rates of PLBI-pTA films against E.coli,P.fluorescens and S.aureus coulde reach 86%,90% and96% respectively,which indicates that the films had good antibacterial effect.The physical damage of bacterial cell membrane after films treatment was confirmed by crystal violet staining and flow cytometry.The DPPH radical scavenging rate of PLBI-pTA films could reach 78.86%,which had good antioxidant effect.During the storage of chilled fresh pork,PLBI-pTA films combined with PA/PE packaging bag was used together.Compared with CK group and PA/PE group,the juice loss rate,p H,total viable count(TVC)and total volatile basic nitrogen(TVB-N)in PA/PE+PLBI-pTA group increased more slowly at the same storage time.Evaluate its shelf life according to various indicators: CK group <PA/PE group <PA/PE+PLBI-2pTA group <PA/PE+PLBI-5pTA group.The combined use of PLBIpTA films had a better preservation effect on chilled fresh pork,which could effectively slow down the growth and reproduction of microorganisms on the meat surface and prolong the shelf life of chilled fresh pork.From the microbial indicators,Stenotrophomonas was the dominant bacteria in fresh meat,accounting for 26.97%.After 8 days of storage,Acinetobacter,Pseudomonas and Stenotrophomonas were the dominant bacteria in CK group,accounting for 21.6%,15.78% and 11.88% respectively.After storage for 20 days,Shewanella,Psychrobacter and Pseudomonas were dominant,and the sum of the three kinds of microorganisms in PA/PE+PLBI-5pTA group,PA/PE+PLBI-2pTA group and PA/PE group was 50.47%,70.78% and 76.9% respectively.During storage,the above three types of microorganisms were the main deterioration factors of cold fresh pork,and the used of PLBI-pTA films could reduce its relative abundance.