Strong STMP-Crosslinked Lignin/Chitosan Hydrogel Films with Enhanced Aqueous Stability and Bioactivity for Active Food Packaging

Abstract

Plastic pollution has intensified globally due to the widespread use of non-biodegradable packaging materials. Conventional passive plastics used in food packaging lack adaptive functionality limiting their preservation efficiency. Biopolymer-based hydrogels offer promise due to their biodegradability, film-forming ability, and intrinsic bioactivity. However, their instability in aqueous environments constrains their application in high-moisture foods such as meat. Lignin extracted from sugarcane tops via acid-alkali treatment and chitosan known for its film-forming and antimicrobial properties were combined to enhance the antioxidant, antimicrobial, UV-blocking, and mechanical performance of the hydrogel. The films were cured at 25 {degrees}C under 80% relative humidity, eliminating the high temperature pre-oven drying required in conventional methods. Further, a stable lignin/chitosan hydrogel film was developed using sodium trimetaphosphate (STMP) as a crosslinker and glycerol as a plasticizer. The films treated with 1% (w/v) STMP for 15 min showed optimal performance, exhibiting 89.89% radical scavenging activity, complete UV shielding, antimicrobial activity against E. coli, and tensile strength of 2364.79 MPa with 31.49% elongation at break. The film retained its integrity in food simulants namely ethanol (10% v/v), acetic acid (3% v/v), and distilled water. In chicken breast packaging trials, the CL-0.8/3Cht film-maintained pH, moisture, and protein stability and significantly reduced microbial load during 5 days of storage. These findings establish the CL-0.8Lig/3Cht hydrogel film with agri-residue derived lignin as a robust, multifunctional, and biodegradable active packaging material for moisture-rich food systems. These findings support waste valorisation advancing cleaner and sustainable food preservation practices.