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 properties 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. Chitosan 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.