Strong STMP-crosslinked lignin/chitosan hydrogel films with enhanced aqueous stability and bioactivity for active food packaging.

Plastic pollution has intensified globally due to the widespread use of non-biodegradable packaging materials. Conventional passive plastics lack adaptive functionality, limiting their preservation efficiency. Although biopolymer-based hydrogels offer biodegradability, film-forming ability, and intrinsic bioactivity, their instability in aqueous environments restricts application in high-moisture foods such as meat. In this study, lignin extracted from sugarcane tops via acid-alkali treatment was incorporated with chitosan films to enhance antioxidant, antimicrobial, UV-blocking, and mechanical performance. The films were air dried at 25 °C, eliminating the high temperature pre-oven conventional drying. Crosslinking was achieved using food-grade sodium trimetaphosphate (STMP) and glycerol as a plasticizer and further cured at 25 °C under 80% RH. The films treated with 1% (w/v) STMP for 15 min showed optimal performance, exhibiting 89.89% radical scavenging activity, significant UV shielding, antimicrobial activity against E. coli, and tensile strength of 44.14 MPa with 158.12% of elongation. The film retained its integrity in ethanol (10% v/v), acetic acid (3% v/v), and distilled water. During chicken breast storage at 25 °C, the CL-0.8Lig/3Cht film-maintained pH, moisture, and protein stability and significantly reduced microbial load over five days. Hence, the present work integrates agri-residue-derived lignin, non-toxic food grade phosphate crosslinking, and mild ambient curing to develop a multifunctional biodegradable hydrogel film specifically engineered for moisture-rich meat packaging applications. These results demonstrate the potential of biomass waste valorization to enable cleaner and more sustainable food preservation, providing a functional alternative to petrochemical plastics within a circular economy framework.