Preparation And Application Of Modified Pullulan As An Antibacterial Material

Pullulan is naturally biodegradable macromolecule and has excellent film-forming property.However,Pullulan shows low antibacterial activity,poor water barrier property and weak mechanical property as a film,which limits its practical application.In order to fully utilize pullulan,it is necessary to modify pullulan to gain antibacterial activity,improve water barrier property and mechanical property.Therefore,in this work,we first modified pullulan by carboxylation,and then grafted D-arginine to develop D-arginine-carboxylated pullulan（Arg-SA-Pul）antibacterial film;In addition,carboxylated pullulan was used as the film forming substrate,and antibacterial agent Nisin and endophytic fungi polysaccharide（GCP）were mixed to develop antibacterial composite films;The antibacterial property,mechanical property,and water vapor permeability of the modified film were studied.Finally,the antibacterial film was used for the preservation of cherries and grapes to investigate the preservation effect.The main research contents are as follows:（1）First,the Arg-SA-Pul was prepared and characterized.Under alkaline conditions,succinic anhydride（SA）underwent esterification reaction with hydroxyl groups on the pullulan（Pul）chain to obtain carboxylated pullulan（SA-Pul）,which is then grafted with D-arginine to obtain Arg-SA-Pul.Using the Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance spectra of SA-Pul and Arg-SA-Pul,it was confirmed that the modification of SA-Pul and Arg-SA-Pul was successful.（2）The bacteriostatic and film property of Arg-SA-Pul as well as the fresh-keeping effects of coating on cherries were explored.Arg-SA-Pul had inhibitory effects on both Staphylococcus aureus and Escherichia coli,with a minimum inhibitory concentration of 45mg·m L^-1 for S.aureus and 55 mg·m L^-1 for E.coli;The water vapor permeability of Arg-SA-Pul film was lower than that of Pullulan film,and its water vapor permeability was the lowest when the glycerol content was 30%in the film system;The tensile strength of pure pullulan film was 15.12 MPa,and the breaking elongation rate was 100.33%.The tensile strength of Arg-SA-Pul film was 19.08 MPa,and the breaking elongation rate was 101.45%;Arg-SA-Pul coated cherries had the lowest degree of depression,darkening and decay.Compared with groups of blank and Pullulan coatings,the cherries with Arg-SA-Pul coatings reduced the weight loss of fruit by 12.53%and 4.23%,hardness loss by 80.4 g and 47.81 g,soluble solid loss by 4.33%and 1.6%,and titrable acid loss by 0.52 g·Kg^-1 and 0.34 g·Kg^-1,respectivey.As a result,this composite filme was able retain moisture,hardness,soluble solids and titratable acids better,demonstrating a good fresh-keeping effect.（3）The antibacterial property,film property,and application and preservation effects of SA-Pul/GCP/Nisin composite solution on grapes were explored.The SA-Pul/GCP/Nisin composite had inhibitory effects on both S.aureus and E.coli,with stronger inhibitory activity against S.aureus than E.coli.The water vapor permeability of SA-Pul/GCP/Nisin composite films was lower than that of Pul/GCP/Nisin composite films,and the water vapor permeability was the lowest when the glycerol content was 30%in the film system.The tensile strength of Pul/GCP/Nisin composite film was 7.65±2.57 MPa,and the tensile strength at break was 106.70±1.88%.The tensile strength of SA-Pul/GCP/Nisin composite film was 13.70±33.33 MPa,and the tensile strength at break was 113.45±1.37%.SA-Pul/GCP/Nissin coated grapes exhibited the lowest degree of depression,darkening and decay.Compared with groups of blank and Pul/GCP/Nisin coatings,the grapes with SA-Pul/GCP/Nisin coatings reduced the weight loss by 3.64%and 1.99%,hardness loss by53.45g and 9.05g,soluble solid loss by 2.20%and 0.63%and titrable acid loss by 0.23 g·Kg^-1and 0.1 g·Kg^-1,respectively.Cosequently,SA-Pul/GCP/Nisin composite film was able to retain water,hardness,soluble solids,and titratable acids better,exhibiting a good fresh-keeping effect.