BACKGROUND In this study, a new crosslinking agent (CA) containing whey protein, papin, glycerin, and epigallocatechin gallate (EGCG), was prepared. The effects of CA content (0, 10, 20, 30, and 40%, v/v) on food packaging properties, crystallinity, microstructure, and antioxidant properties of pectin‐CA and chitosan‐CA composite films were analyzed. The results of this research offer a theoretical basis for engineering improved films for food packing. RESULTS Pectin‐CA (30%) and chitosan‐CA (40%) composite films showed the best light transmission, water retention, breathability, plasticity, and antioxidant activity. Scanning electron microscopy revealed that these composite films exhibited a uniform and homogeneous structure without obvious pores. Fourier‐transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) indicated that the amino acids and EGCG in CA were bonded to the film substrate (pectin/chitosan) via electrostatic interactions, hydrogen bonding, and covalent bonding, which led to an improvement in the film's properties. CONCLUSION The CA has broad application prospects in food packaging as a cross‐linking agent and antioxidant. © 2022 Society of Chemical Industry.