Bio-derived active film with integrated antibacterial, antioxidant, UV-shielding and pH-responsive properties for food packaging

With growing public expectations for high food quality and safety, polysaccharide-derived active packaging films with integrated functionalities have attracted increasing interest. Herein, a multifunctional, pH-responsive film was fabricated from carboxymethyl chitosan (CMCS) and sodium alginate (SA) using glycerol as a plasticizer, in which a coupled network was constructed via Zn 2+ coordination crosslinking and tea polyphenol (TP) hydrogen-bonding/coordination synergy. The resulting CMS-Zn-TP film exhibited reinforced mechanical performance (tensile strength of 27.2 MPa and elongation at break of 38.9%), improved water-vapor barrier properties (WVP of 3.30 × 10 −10  g·s −1 ·m −1 ·Pa −1 , compared with 4.12 × 10 −10  g·s −1 ·m −1 ·Pa −1 for the CMS film), and pronounced UV-shielding capability as evidenced by UV–Vis spectra over 200–800 nm with enhanced shielding in the 200–400 nm region after TP incorporation. Owing to the combined antibacterial contributions of Zn 2+ and TP, the film achieved antibacterial efficiencies of 93.5% against Escherichia coli and 92.9% against Staphylococcus aureus . In addition, the film showed pH-triggered release behavior: when the pH decreased below 6, decomplexation of the coordination-crosslinked structure promoted the release of Zn 2+ and TP. The CMS-Zn-TP film also exhibited strong antioxidant capacity, with DPPH and ABTS radical-scavenging activities of 90.3% and 95.4%, respectively, contributing to the preservation of fruit quality during 9-day storage. Notably, Zn 2+ migration and long-term safety/stability still require further systematic evaluation for food-contact applications. Overall, this work provides a feasible strategy for developing sustainable and functional active packaging materials.