Antioxidant packaging films developed based on chitosan grafted with different catechins: Characterization and application in retarding corn oil oxidation

Four catechins including (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epigallocatechin gallate (EGCG) were conjugated onto chitosan (CS) molecules via ascorbate radical mediated reaction, producing EC-g-CS, ECG-g-CS, EGC-g-CS and EGCG-g-CS. The four catechin-g-CSs were individually blended with CS to develop food packaging films. The structure, physicochemical properties and antioxidant activity of four catechin-g-CSs as well as their corresponding packaging films were compared. Results showed the total phenol content differed in four catechin-g-CSs, where ECG-g-CS and EGCG-g-CS had higher total phenol contents than EC-g-CS and EGC-g-CS. Four catechin-g-CSs showed the characteristic UV–vis, infrared and nuclear magnetic resonance signals of catechins, revealing the successful conjugation of CS with catechins. Antioxidant activity of CS was elevated by catechins to different degrees, with EGCG-g-CS having the highest antioxidant activity. The developed CS/catechin-g-CSs films showed larger thickness, water solubility, tensile strength, elongation at break, thermal stability and antioxidant activity but lower light transmittance, water contact angle, water vapor and oxygen permeability in comparison with CS film. Meanwhile, CS/catechin-g-CSs films had good anti-permeability against corn oil and effectively retarded the increase of thiobarbituric acid reactive substance and peroxide value levels during oil storage. Findings showed CS/catechin-g-CSs films were ideal antioxidant packaging materials for edible oils.