Tannic acid cross-linked bitter vetch protein/polyvinyl alcohol composite films with multifunctional properties for sustainable food packaging

Biopolymer-based films often suffer from weak mechanical and barrier properties, limiting their use in sustainable food packaging. In this study, bitter vetch seed protein (B) and polyvinyl alcohol (P) were combined with tannic acid (TA) as a cross-linker to prepare biodegradable composite films. The films were characterized for mechanical, barrier, thermal, chemical, antibacterial, antifogging, and self-healing properties. The cross-linked films exhibited significantly improved elongation at break (from 3.39 % in B film to 131.40 %) and reduced water vapor permeability (from 6.05 × 10⁻⁸ to 3.50 × 10⁻⁸ g/Pa·s·m) compared with the neat films. ATR-FTIR analysis confirmed strong interactions between the polymers and TA, while TGA indicated enhanced thermal stability, with decomposition temperatures reaching 490 °C compared with 455 °C and 423 °C for B and P films, respectively. The films also demonstrated effective antibacterial and antifogging properties. When applied to strawberries, the cross-linked films successfully prolonged shelf life at both room and refrigerated temperatures. These results suggest that B/P films cross-linked with TA are promising biodegradable packaging materials for perishable foods. • Bitter vetch protein/polyvinyl alcohol films cross-linked with tannic acid. • Biodegradable cross-linked films improved mechanical and barrier performance. • Tannic acid enhanced hydrophobicity, optical, and antibacterial traits. • Films showed antifogging and self-healing properties. • Cross-linked films preserved strawberries for 5 days at 25 °C.