Violacein-containing chitosan as light-sensitive, antioxidant and antibacterial hydrogels towards sustainable food packaging

Abstract

Naturally derived biodegradable polymers offer sustainable alternatives to fossil-based plastics in food packaging. In this study, multifunctional packaging films were prepared by integrating biomass-derived chitosan with violacein, a biotechnologically synthesized pigment. The resulting violacein–chitosan networks formed light-responsive hydrogels that could be cast into films or applied as coatings. Successful incorporation of violacein was confirmed by FTIR and UV–Vis analyses, supported by distinct optical and photoluminescent properties. SEM imaging revealed increased surface roughness and pigment aggregation at higher violacein loadings. Water solubility (WS) decreased markedly from 72.23% for pure chitosan to 19.33% for CS@Vio10%-f, while water vapor permeability (WVP) decreased from 8.09×10⁻⁹ to 4.33×10⁻⁹ g·m/(s·Pa). Contact angle measurements indicated enhanced hydrophobicity, increasing from 74.3° (pristine chitosan) to 107.3° (CS@Vio10%-f). Violocaein incorporation allows at 5% optimal loading to improve both tensile strengh (56 MPa), Young modulus (1360 MPa) and elongation at break (51%), a unique behaviour that can be rooted in the bifacetted structure of the pigment, acting simultanously as plasticizer and stifenning reagent. Violacein endowed also the films with remarkable UV-shielding (up to 87.8% UVA and 98.9% UVB protection) and antioxidant properties, with radical scavenging activity reaching 75% at 10% violacein loading. Antibacterial assays showed up to 80% inhibition of S. aureus and 71% of E. coli, outperforming pristine chitosan (60% and 65%, respectively). Furthermore, the films effectively extended the shelf life of strawberries, blueberries, and raspberries. Overall, these findings highlight the potential of violacein–chitosan films as sustainable, multifunctional materials for active food packaging and preservation.