The Synergistic Impact of Polyphenols on Collagen Fiber–Starch Composite Films for Enhanced Physical Integrity and Antioxidant Capacity

Edible films are increasingly recognized as promising sustainable packaging alternatives, but often face challenges such as poor mechanical strength, limited barrier properties, and low oxidative stability. This study aimed to enhance the physicochemical performance of collagen fiber-starch composite films by incorporating polyphenols (including tannic acid (TA), caffeic acid (CA), and their oxidized forms, OTA and OCA) as natural cross-linkers and antioxidants. Results showed that the addition of 0.1% TA increased the tensile strength by approximately 45% compared to the control, while simultaneously reducing the water vapor permeability from 1.32 to 1.26 g·mm/kPa·h·m², with TA outperforming CA due to its higher molecular weight and stronger intermolecular interactions. Oxidized polyphenols further improved the mechanical and water vapor barrier properties via quinone-induced covalent cross-linking, thereby forming a denser film network. The films also exhibited enhanced UV-visible light shielding, with nearly complete ultraviolet blockage (transmittance is close to zero in the 200-280 nm range). Non-oxidized polyphenols showed higher antioxidant activity in the ABTS and reducing power assays, while release kinetics analysis revealed the highest release rate in 50% ethanol, indicating a pronounced solvent-dependent behavior. Specifically, films with 0.1% TA exhibited an ABTS radical scavenging activity of over 80%, significantly higher than the control. Overall, polyphenols effectively improve film performance through cross-linking and structural modification, offering a theoretical foundation for designing active packaging for targeted food systems.