Preparation, characterization and application of antioxidant packaging films based on chitosan-epicatechin gallate conjugates with different substitution degrees

Abstract

In this study, chitosan (CS) was conjugated with epicatechin gallate (ECG) to prepare CS-ECG conjugates with different substitution degrees (5.18 %, 6.36 % and 7.74 %). Then, antioxidant packaging films were fabricated by blending CS and CS-ECG conjugates. The impact of CS-ECG conjugates' substitution degree on the functionality of CS/CS-ECG films was determined. CS-ECG conjugates showed UV absorption at 275 nm, proton signal at 6.85 ppm and infrared absorption at 1533 cm−1, assigning to the conjugated ECG. As compared with CS, CS-ECG conjugates exhibited less crystalline state but higher antioxidant activity. The structural characterization of CS/CS-ECG films showed CS and CS-ECG conjugates formed hydrogen bonds. CS/CS-ECG films displayed 26.35 %–29.23 % water solubility, 85.61°–86.96° water contact angle, 3.11–3.41 × 10−11 g m−1 s−1 Pa−1 water vapor permeability, 0.29–0.34 cm3 mm m−2 day−1 atm−1 oxygen permeability, 31.54–36.20 MPa tensile strength, 50.12 %–56.40 % elongation at break, as well as potent antioxidant activity and oil oxidation inhibitory ability. Notably, the film containing CS-ECG conjugate with 7.74 % substitution degree had the strongest barrier ability, mechanical property, antioxidant activity and oil oxidation inhibitory ability. Results suggested the substitution degree of CS-ECG conjugates was positively correlated with the barrier, mechanical and antioxidant properties of CS/CS-ECG films.