Synthesis Of Chitosan-hydroxybenzoic Acid Graft Copolymer Film And Its Fresh-keeping Effect On Agaricus Bisporus

Five kinds of hydroxybenzoic acids including gallic acid(GLA),gentisic acid(GTA),protocatechuic acid(PA),syringic acid(SA)and vanillic acid(VA)were individually grafted onto chitosan(CS)through carbodiimide mediated coupling reaction.The obtained hydroxybenzoic acid grafted CS(hydroxybenzoic acid-g-CS)were further developed into films by casting.The physical,mechanical and antioxidant properties of hydroxybenzoic acid-g-CS films were compared for the first time.As a result,GLA grafted CS(GLA-g-CS)film was selected for its best performance.The effect of GLA-g-CS film on the postharvest quality of Agaricus bisporus was investigated in details.(1)Five kinds of hydroxybenzoic acids were individually grafted onto CS by EDC mediated coupling reaction.The structures and physicochemical properties of hydroxybenzoic acid-g-CSs were investigated.The grafting ratios of hydroxybenzoic acid-g-CSs varied from 34.9 to 111.0 mg/g and hydroxybenzoic acid-g-CSs exhibited significant UV-vis absorption peaks in the range of 250 to 600 im.As compared with native CS,the relative intensity of bands at 1596 cm-1 and 1654 cm-1 in hydroxybenzoic acid-g-CSs somewhat decreased.This indicated the formation of amide linkage between amino groups of CS and carboxyl groups of hydroxybenzoic acids.Moreover,new bands appeared at about 1730 cm-1 in hydroxybenzoic acid-g-CSs,assigning to the C=O stretching of ester groups.Hydroxybenzoic acid-g-CSs exhibited all the proton signals of CS as well as some new chemical shifts in the range of 6.0 to 8.0 ppm.These new proton signals in hydroxybenzoic acid-g-CSs could be assigned to the aromatic protons of hydroxybenzoic acid moieties.The intensity of characteristic diffraction peak of CS at 2θ= 20° significantly decreased after grafting with hydroxybenzoic acids.In addition,the diffraction peak of CS at 2θ= 11° almost disappeared in the final grafted products.These results suggested the grafting of hydroxybenzoic acid onto CS had remarkably decreased the original crystallinity of CS.(2)The physical,mechanical and antioxidant properties of hydroxybenzoic acid-g-CS films were compared for the first time.Hydroxybenzoic acid-g-CS films exhibited better UV light and moisture barrier properties as compared with CS film.Most hydroxybenzoic acid-g-CS films showed higher tensile strength and elongation at break than CS film.The surface morphology of CS film became rough after grafting with hydroxybenzoic acid.Antioxidant activity assays showed hydroxybenzoic acid-g-CS films had higher DPPH scavenging activity than CS film.As compared to CS and other hydroxybenzoic acid-g-CS films,GLA-g-CS film possessed the highest UV light and moisture barrier,mechanical and antioxidant properties.(3)GLA-g-CS film was used as a novel active packaging material for the preservation of Agaricus bisporus.Effect of GLA-g-CS film packing on the physico-chemical parameters and enzyme activities of A.bisporus during cold storage was investigated.As compared to mushrooms packed with CS film and commercially used polyethylene(PE)film,mushrooms packed with GLA-g-CS film showed much higher firmness but significantly lower respiration rate,browning degree,malondialdehyde content,electrolyte leakage rate,superoxide anion production rate and hydrogen peroxide content.Besides,mushrooms packed with GLA-g-CS film exhibited the highest superoxide dismutase and catalase activities as well as total phenolic content,but the lowest polyphenol oxidase activity among all the treatment groups.Our results suggested GLA-g-CS film packing could increase the antioxidant status of A.bisporus,which in turn maintained the postharvest quality of mushrooms.