Integrating sustainability and nutrition: comprehensive valorisation of vegetable by-products for bioactive food applications

Abstract

Valorising vegetable by-products is a sustainable and innovative strategy to reduce food waste and develop functional ingredients. This study investigated onion peel (Allium cepa L.), kale (Brassica oleracea L. var. Acephala), zucchini (Cucurbita pepo L.), and their combined mixture, materials often discarded as a result of market quality standards. Hydroethanolic extracts and their solid residues were analyzed. The extracts were evaluated for their phenolic content and antioxidant, antidiabetic, and antimicrobial activities. The residues were assessed for their proximate and chemical composition to support their valorization within a zero-waste strategy. Onion peel extract showed the highest phenolic content and antioxidant capacity, with strong α-glucosidase inhibition (IC50: 64.4 µg/mL). Additionally, onion peel and kale extracts showed antimicrobial activity. Among residues, onion peel had the highest dietary fiber (69 g/100 g), and zucchini had the highest protein content (30.7 g/100 g), including essential amino acids. This integrated and scalable approach adds value to both extract and residue, promoting sustainable, circular food systems aligned with the Sustainable Development Goals of the 2030 Agenda.