Development of antioxidant chitosan-based films incorporated with chitooligosaccharide-caffeic acid conjugates

Chitooligosaccharide-caffeic acid (COS-CA) conjugates with three different grafting degrees were synthesized by the N, N '-carbonyldiimidazole (CDI) mediated method and used as functional components to prepare antioxidant chitosan-based composite films. The effects of the synthesized conjugates on the physical and biological prop-erties of chitosan-based films, including mechanical property, UV-barrier property, optical, water vapor permeability, thermal stability, degradation behavior in soil, and antioxidant activity, were investigated. Chi-tosan acetate films with chitooligosaccharide or without other additives were used as the control. The results showed that the incorporation of COS-CA conjugates caused significant increases in mechanical property, color difference, and UV-barrier property without affecting thermal stability of films and endowed the chitosan-based films with excellent DPPH radical scavenging ability and reducing capacity. Moreover, the grafting ratios of caffeic acid in COS-CA conjugates had a noticeable influence on these changes of chitosan-based composite films. Overall, chitosan/COS-CA conjugates composite films with great UV-barrier property and excellent antioxidant activity could be developed as biodegradable antioxidant biomaterials for food packaging.