Waste-to-Packaging: Biodegradable Chitosan Films Reinforced With Polyphenol-Rich Olive Agro-Residues

The replacement of fossil-based plastics with active, biodegradable packaging derived from renewable resources is a critical step toward a sustainable and circular economy. In this work, we introduce an integrated waste-to-packaging strategy that transforms chitosan extracted from shellfishery by-products and olive oil agro-residues (olive mill wastewater and olive pomace) into mechanically-sustained, antioxidant, and antimicrobial coating films. Initially, model chitosan films were engineered by incorporating syringic and caffeic acids, followed by the direct utilization of crude agricultural waste extracts as polyphenol-rich additives. Notably, agro-waste was successfully incorporated into the chitosan films at 5%, 10%, 20%, and 50% without compromising their formation, quality, or flexibility. The mechanical properties of the films have been improved significantly, with tensile strength (TS) reaching 62 MPa for caffeic acid-enriched films (20%) compared to 35 MPa for pristine chitosan films. Antioxidant capacity was markedly enhanced, with films enriched with caffeic acid reaching 99.4% inhibition in the ABTS radical scavenging assay. The antimicrobial activity was broad-spectrum, with the films showing up to 90% inhibition against S. aureus and S. epidermidis, and 50% inhibition against P. aeruginosa. Biocompatibility assessments confirmed negligible hemolytic and cytotoxic effects, with cell viability reaching up to 115% for syringic acid-modified films at 20% concentration. This metal-free and synthetic additive-free approach not only valorizes two major agro-industrial waste streams but also delivers cost-effective, multifunctional packaging materials, offering a scalable solution to both plastic pollution and organic waste disposal.