Upcycling onion peels for enhanced gas barrier and antioxidant bioplastics based on starch from potato processing slurries.

The upcycling of food waste into high-value materials presents a key opportunity for sustainable waste management. While onion peel (OP) extracts have been investigated as additives for bioplastics, this study explores the direct incorporation of whole powdered OP (5-20 wt%) into starch-based films, eliminating extraction steps and fully valorizing this agro-industrial by-product. Using starch recovered from potato processing slurries as the polymeric matrix, the influence of OP on film structure, mechanical performance, water resistance, gas permeability, and antioxidant activity was evaluated. Chemical analysis of OP revealed a composition of 47% alcohol insoluble compounds (mainly pectin and cellulose), 12% alcohol soluble matter (primarily glucose-based carbohydrates), 6% lipids, 2%proteins, 5% gallic acid equivalents, and 27% ashes. The direct incorporation of powdered OP resulted in natural pigmentation, producing transparent films with an orangish hue. This approach enhances the aesthetic properties of films while eliminating the need for artificial dyes, contributing to a more sustainable product design. The developed bioplastics exhibited enhanced mechanical properties and improved water resistance, making them attractive for sustainable packaging applications. At OP concentrations above 10 wt%, Young's modulus increased from 1214 MPa to 1496 MPa, while tensile strength and elongation at break decreased from 31.4 MPa to 24.6 MPa and from 4.5% to 2.1%, respectively. Water contact angles increased from 75° up to 87°, and water vapor permeability was reduced by up to 60%, improving moisture resistance. Importantly, OP incorporation did not compromise oxygen (O2), carbon dioxide (CO2), or nitrogen (N2) barrier properties and imparted significant antioxidant activity, with 20 wt% OP-based films inhibiting 93% of the 2.2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic) acid radical cation (ABTS.+) after 6 h. This study presents an innovative waste-to-resource strategy that eliminates processing waste, aligns with circular economy principles, and demonstrates the first use of whole OP as a multifunctional additive in starch-based bioplastics. By replacing conventional extraction-based approaches, this method enhances material sustainability while promoting a scalable, zero-waste approach to packaging development.