Preparation Of Hydroxycinnamic Acid Grafted Citosan Film And Its Preservation Effect On Pork

Chitosan(CS)is the partially or completely deacetylated product of chitin by concentrated alkaline solution treatment.CS has the advantages of non-toxicity,biodegradability and biocompatibility.In recent years,in order to improve the solubility and biological activity of CS,researchers have grafted phenolic acids onto CS molecules through graft copolymerization reactions.As a result,the application of CS in food has been greatly broadened.In this study,1-(3-dimethylaminopropyl)-3-ethylcarbodiimide(EDC)/N-hydroxysuccinimide(NHS)mediated chemical cross-linking reaction was used to synthesize three different hydroxycinnamic acid grafted CSs.The structural characteristics,film-forming properties and the preservation effect of the graft copolymers on pork were systematically investigated.The obtained results are of great significance to broaden the applicationof hydroxycinnamic acid grafted CSs in food industry.(1)Three kinds of hydroxycinnamic acid grafted CSs were prepared by EDC/NHS mediated chemical cross-linking reaction,namely,coumaric acid-g-CS,caffeic acid-g-CS and ferullic acid-g-CS.The structural and film forming characteristics of the graft copolymers were studied.Results showed the grafting rates of coumaric acid-g-CS,caffeic acid-g-CS and ferullic acid-g-CS were 73.68,129.42 and 91.75 mg/g,respectively.Thin layer chromatography proved the graft copolymer did not contain free phenolic acids.UV-visible absorption spectroscopy showed the graft copolymer have significant ultraviolet absorption peaks in the range of 200-400 nm.Infrared spectroscopy proved CS and phenolic acids were covalently linked by amide and ester bonds.X-ray diffraction pattern showed phenolic acid grafting significantly reduced the semi-crystalline properties of CS.Hydroxycinnamic acid grafted CSs were further prepared into films by casting.It was found that phenolic acid grafting increased the thickness,the barrier properties to ultraviolet light and water vapor,mechanical properties,antioxidant and antibacterial activity of the films Among all the films,caffeic acid-g-CS film had the strongest ultraviolet light and water vapor barrier properties,mechanical properties,antioxidant and antibacterial activity.Results proved the performance of the film was closely related to the type of phenolic acid grafted,the graft ratio and the internal structure of the film.(2)The preservation effect of caffeic acid-g-CS film on pork was further studied and compared with that of PE and CS films.As compared with PE film,CS and caffeic acid-g-CS film packaging could effectively inhibit the increase of pH value,lipid peroxidation degree,total volatile basic nitrogen content and total colony count of pork during cold storage,and could effectively relieve the decrease of color value(L and a values),texture characteristics(hardness and elasticity)and sensory characteristics of pork.The pork packaged in PE film was badly spoiled after being refrigerated for 7 days,while the pork wrapped in CS and caffeic acid-g-CS films deteriorated seriously at the 9th and 11th days,respectively.Therefore,compared with PE film,caffeic acid-g-CS film packaging could extend the shelf life of refrigerated pork by 4 days.The preservation effect of caffeic acid-g-CS film on pork was related to its lower water vapor transmission rate and higher antioxidant and antibacterial activity.