Tyrosinase And Laccase Catalyzed Grafting Reaction Between Different Phenolic Acids And Chitosan

This research used chitosan of low degree as the reaction substrate,used laccase and tyrosinase respectively to catalyze the grafting reaction between chitosan and ferulic acid,protocatechuic acid and gallic acid,each of which contains a,2 and 3 phenolic hydroxyl.Performance changes and catalytic effect of the grafted products were compared with the chitosan samples,and effects of different phenolic hydroxyl content of phenolic acids on the grafting reaction were explored.Catalytic mechanism of two enzymes in the grafting reaction was initially explored.The changes of functional groups of chitosan before and after grafting reaction were tested by FTIR;grafting principle of the reaction was determined by Py-GC/MS detection;structural stability of the material molecules of chitosan before and after grafting reaction was detected by TGA.Through the test of product structure change by using FTIR,it was clear that both of two enzymes could catalyze grafting reaction successfully and the amino of reaction products and chitosan were subjected to schiff base type covalent modification Through TGA analysis of products,it was found that thermal stability of both grafted products were improved,the success of grafting reaction between phenolic acids and chitosan can be verified,and the thermal stability improvement of tyrosinase catalyzed graft products was bigger than that of laccase.Through Py-GC/MS detection,it was found that grafting reactions catalyzed by the two enzymes generated derivatives by connecting chemical bond,but not the physical adsorption onto the surface of chitosan.The antioxidation property of products obtained from the laccase and tyrosinase catalyzing grafting reaction between three kinds of phenolic acids and chitosan were remarkably improved.The chitosan-phenolic acids grafted product catalyzed by laccase was found to have a 60%higher radical scavenging rate than that of chitosan,and the chitosan-phenolic acids grafted product catalyzed by tyrosinase was found to have a 40%higher radical scavenging rate than that of chitosan.Comparing grafted products of the three kinds of phenolic acids,the grafted product between gallic acid and chitosan had a higher antioxidation property,and the laccase catalyzed grafted product has the highest radical scavenging rate,82%.The antioxidation property of laccase catalyzed grafted product was better than that of tyrosinase catalyzed grafted product.Different chitosan-phenolic acids grafted product had varied antioxidation properties,and the ranking order are:chitosan-gallic acid>chitosan-protocatechuic acid>chitosan-ferulic acid>chitosan sample.Testing results of the reducing property also confirmed the conclusion.Compared with the original chitosan samples,the grafted products had better hygroscopic properties,and the grafted products catalyzed by tyrosinase or laccase have basically the same change magnitude of hygroscopic properties.In an environment of 81%relative humidity,grafted products between phenolic acids and chitosan catalyzed by laccase showed a 22%higher hygroscopic property than original chitosan sample,and grafted products between phenolic acids and chitosan catalyzed by tyrosinase showed a 23%higher hygroscopic property than original chitosan sample.