Citric Acid‐Crosslinked Chitosan Coatings Incorporating Curcumin for Enhancement of Antioxidant and Antimicrobial Properties

A fully bio-based coating for packaging applications was developed utilizing chitosan (CHI) dissolved in citric acid (CA) solution, which served simultaneously as a green solvent and crosslinker, further enriched with curcumin (CUR). These active formulations were evaluated as freestanding membranes and as coatings on a biodegradable substrate before and after Dry Heat Treatment (DHT) for 3, 5, and 21 h. FTIR analysis confirmed that DHT drove a transition from ionic interactions to covalent amide bonds, improving thermal stability and water resistance. Upon 21 h of DHT, CHI/CA exhibited a marked reduction in vapor swelling (from 155.0% to 16.2%) and water-soluble fraction (from 35.5% to 16.3%), with a similar trend observed for CHI/CA/CUR (from 190.5% to 53.7% and from 40.9% to 26.7%, respectively), demonstrating significant network densification. DMTA results supported this trend, revealing an increase in rigidity of crosslinked samples. Functionally, the DPPH radical scavenging activity of curcumin-loaded films increased from 12.4% to a peak of 28.8% after 5 h of DHT due to amidation-driven matrix reorganization. Antimicrobial surface efficacy against four pathogens was observed exclusively under direct-contact conditions, due to curcumin immobilization within the matrix. Although DHT generally reduced antimicrobial capacity, curcumin partially restored activity. Overall, this system provides a sustainable active coating suitable for shelf-life extension.