Next-generation chitosan biodegradable films reinforced with bioactive acid-DES: A sustainable solution for improved mechanical, antibacterial, and anti-browning properties.

The growing demand for sustainable and active food-packaging materials has increased interest in biodegradable biopolymers with improved functional performance. This study developed multifunctional chitosan (CS) films incorporating deep eutectic solvents (DESs) as green bioactive plasticizers to improve antioxidant, antibacterial, and mechanical properties. DESs were prepared using choline chloride with five organic acids, including citric (CA), malic (MA), oxalic (OA), lactic (LA), and ascorbic acids (AA), and the resulting DESs were evaluated for antioxidant and antibacterial activities. AA-DES and OA-DES showed the highest activities and were incorporated into CS films individually and combined (CS-AA-OA) at 1% concentration. Structural characterization (FTIR, XRD, SEM, TGA) and functional assessments were conducted to evaluate mechanical, thermal, and bioactive performance. The CS-OA film exhibited superior mechanical strength (56.42 MPa; 9.10% EB), while CS-AA-OA achieved the highest radical-scavenging activity (DPPH 88.15%, ABTS 98.44%) and strong antibacterial efficacy against E. coli (24.7 ± 0.34 mm) and S. aureus (22.8 ± 0.52 mm). The soil burial test confirmed excellent biodegradability, and coating applications on mushrooms and bananas effectively reduced browning, weight loss, and firmness degradation. The combined incorporation of AA-DES and OA-DES enhanced CS film structure and bioactivity, providing a sustainable, high-performance material for active food packaging.