Preparation And Application Of Catechin Monomer-Chitosan Conjugate Films

Chitosan has ideal film forming,safety and antibacterial activity,and has broad application potentials in the field of food packaging.However,the mechanical properties of chitosan films are poor.Meanwhile,the application of chitosan films in food active packaging is also limited by their weak antioxidant capacity.Therefore,it is necessary to modify chitosan molecules to improve the properties of chitosan films.In this study,four different catechin monomers((-)-epicatechin,(-)-epigallocatechin gallate,(-)-epigallocatechin gallate and(-)-epigallocatechin gallate)were grafted onto chitosan by free radical-mediated method to synthesize catechin monomer-chitosan graft copolymers,and then the graft copolymers were prepared into films.The properties of different catechin monomers-chitosan graft copolymer films and the epigallocatechin gallate-chitosan graft copolymer films with different grafting degrees were determined.The results of this study are summarized as follows:(1)Four different catechin monomers were grafted onto chitosan by free radical-mediated method,and the obtained catechin monomer-chitosan graft copolymers were characterized.The structural characteristics and antioxidant activity of the graft copolymer were studied.The results showed that(-)-epicatechin gallate-chitosan graft copolymer had the highest graft degree(74.4 mg ECG/g).The results of thin layer chromatography,ultraviolet visible spectrum,Fourier-transform infrared spectrum and nuclear magnetic resonance spectrum showed that catechin monomers were successfully grafted onto chitosan.X-ray diffraction pattern showed that the crystallinity of chitosan decreased after grafting.The results of scanning electron microscopy showed that the graft copolymers were flaky and filamentous.Grafting catechin monomer could significantly improve the free radical scavenging ability and reducing power of chitosan.Furthermore,the graft copolymers were added to chitosan matrix to prepare packaging films.The structure,physical and chemical properties,antioxidant activity,and the packaging effect of the films on corn oil were determined.Results showed that the graft copolymers could significantly enhance the barrier performance,mechanical properties and oxidation resistance of chitosan film to ultraviolet light and oxygen.Graft copolymer film packaging could delay the oxidation process of corn oil during storage.Among them,epicatechin gallate-chitosan graft copolymer film had the best packing effect.(2)Three epicatechin gallate-chitosan graft copolymers with different grafting degrees were successfully prepared by graft copolymerization reaction of chitosan and epicatechin gallate in the molar ratio of 2:1,1:1 and 1:2.Results showed that the grafting degrees of three graft copolymers were 51.79,63.6 and 77.4 mg ECG/g,respectively.The results of thin layer chromatography,ultraviolet visible spectrum,Fourier-transform infrared spectrum and nuclear magnetic resonance spectrum showed that epicatechin gallate-chitosan graft copolymers were successful prepared.The antioxidant activity of graft copolymers was positively correlated with their grafting degree,Afterwards,the graft copolymers were added into chitosan matrix to prepare packaging films.The structure,physical and chemical properties,antioxidant activity,and the packaging effect of the films on corn oil were determined.Results showed that the water vapor permeability and oxygen permeability of chitosan film were decreased by 4.48%-12.89%and 19.05%-30.95%,respectively.The elongation at break and tensile strength of the films were increased by 30.68%-46.48%and 12.87%-29.56%,respectively.The graft copolymers significantly improved the antioxidant capacity of chitosan film and the active packaging effect of corn oil.Among them,epicatechin gallate-chitosan graft copolymer membrane with the highest grafting degree had the best packing effect.