Onion waste based-biorefinery for sustainable generation of value-added products

•Onion waste is generated through industrial, domestic and postharvest losses.•Fermentation, extraction and hydrolysis are mostly used for onion waste biorefineries.•Organic acids, pigments, and bioactives can be generated from onion waste.•Chemico-mechanical methods for different onion waste classes are currently needed.•Co-production of acids, polyphenols or enzymes from onion waste may be attempted.