Interfacial Engineering of Tannic Acid‐Cross‐Linked Chitosan–Gelatin Biofilms for Advanced Antimicrobial Packaging Applications

ABSTRACT

Biopolymer‐based films have emerged as promising alternatives for sustainable food packaging; however, their practical implementation remains limited by insufficient mechanical stability and sensitivity to humid environments. This work establishes concentration‐dependent structure–property relationships governing supramolecular cross‐linking in tannic acid‐engineered chitosan–gelatin biofilms (CS/GEL), revealing a transition from network reinforcement at low tannic acid contents to plasticization‐induced deterioration at higher concentrations. TA was incorporated at concentrations ranging from 0.01% to 0.1% (w/v) to modulate intermolecular interactions and tailor the supramolecular organization of the polymer network. Mechanical analysis revealed that low TA concentrations (0.01%–0.05% w/v) enhanced the yield stress from 27.4 MPa in the control film to 32.5 and 31.4 MPa, respectively, indicating improved structural reinforcement through hydrogen bonding and supramolecular interactions between TA and polymer chains. In contrast, higher TA content (0.1% w/v) significantly reduced mechanical performance, suggesting that excessive TA reduces the efficiency of intermolecular organization and promotes plasticization‐like behavior. Complementary physicochemical characterization, including swelling behavior, water solubility, contact angle, FTIR, and thermogravimetric analysis, confirmed concentration‐dependent modulation of network structure, surface hydrophilicity, and thermal stability. Antibacterial assays demonstrated that TA incorporation enhanced the antibacterial performance of the films, with the most pronounced improvement observed against Staphylococcus aureus after 24 h of contact, whereas more moderate responses were obtained for the Gram‐negative strains. The results highlight the dual functionality of TA as a natural cross‐linking and antimicrobial agent. Overall, this study provides insights into concentration‐driven structure–property relationships in tannic acid‐cross‐linked chitosan/gelatin biofilms, demonstrating their potential as tunable, multifunctional, and sustainable materials for advanced antimicrobial food packaging applications.