Preparation and characterization of protocatechuic acid grafted chitosan films with antioxidant activity

In this study, novel chitosan (CS) based active films were developed by grafting natural phenolic antioxidant of protocatechuic acid (PA) onto chitosan backbones. The physicochemical, mechanical and antioxidant properties of three PA grafted CS (PA-g-CS) films with different grafting ratios were characterized. The transparent PA-g-CS films exhibited yellowish color with thickness ranging from 44.1 to 48.6 μm. By contrast with CS film, PA-g-CS films with medium and high grafting ratios showed decreased moisture content, water vapor permeability; however, increased water solubility and tensile strength. The barrier to UV light of CS film could be improved by grafting with PA. An increase in the total color difference was observed for PA-g-CS films, indicating PA-g-CS films were more colored. Among four kinds of films tested, PA-g-CS film with medium grafting ratio exhibited the highest tensile strength (45.7 MPa) and elongation at break (5.05%). According to thermogravimetric analysis, the maximum rates of weight loss for PA-g-CS films appeared at 291.8–294.0 °C. Antioxidant activity assays showed that PA-g-CS films had both dose-dependent and time-dependent scavenging activity on DPPH radical. Our results suggest that PA-g-CS films are expected to serve as novel antioxidant food packaging materials.