| Chitosan is naturally non-toxic and has good antibacterial,biocompatibility,and degradability properties,so it has a wide range of applications in food,medicine,and other industries.Chitosan also has good film forming properties and is therefore a good choice for preparing edible coating.Moreover,the structure of chitosan contains amino and hydroxyl groups,so its physicochemical properties can be improved by chemical reactions.In this study,two proanthocyanidin-chitosan conjugates（PA-CS1 and PA-CS2）were prepared by grafting proanthocyanidin onto two different molecular weight chitosan by grafting,their structures were characterized,and their biological activities were studied.Firstly,proanthocyanidin-chitosan conjugates were prepared by free radical grafting reaction,and the preparation conditions were optimized by single factor experiments.The PA content in PA-CS1 and PA-CS2 was 381.76 mg PAE/g and 340.93 mg PAE/g,respectively.The successful syntheses of proanthocyanidin-chitosan conjugates were confirmed by FTIR,UV-vis,and 1H NMR,and the grafting reaction mainly occurred on the amino and C6hydroxyl groups of chitosan.XRD showed that the cystallinity of the conjugates were reduced after grafting.Next,the antioxidant activities of proanthocyanidin-chitosan conjugates were investigated.The results showed that both PA-CS1 and PA-CS2 had the strong radical scavenging ability and reducing power.The IC50values of PA-CS1 and PA-CS2 for ABTS radicals were 5.9μg/m L and 5.5μg/m L,respectively.Then,the antibacterial activities of the proanthocyanidin-chitosan conjugates were investigated.The results showed that the conjugates inhibited the growth of Escherichia coli,Staphylococcus aureus,Micrococcus luteus,Bacillus subtilis and Proteus vulgaris.The inhibitory effects on Micrococcus luteus and Bacillus subtilis were the best.The MIC of PA-CS1 on the two bacteria was 128μg/m L.The MIC of PA-CS2 on the two bacteria was 64μg/m L.Finally,the preservation effect of PA-CS2 on fresh-cut pineapple was studied.During cold storage,compared with the untreated control,the edible coating prepared by PA-CS2reduced the loss of nutrients of fresh-cut pineapple,such as vitamin C and total phenols,and kept the pineapple with high antioxidant capacity.PA-CS2 inhibited the activities of PPO and POD,which could reduce the browning and deterioration of pineapple.The results indicate that proanthocyanidin-chitosan conjugate has a preservation effect on fresh-cut pineapple. |
