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.