Onions: A Source of Flavonoids

Flavonoids are a large and diverse group of polyphenolic compounds with antioxidant effects, and onion (Allium cepa L.) is one of the richest sources of dietary flavonoids. Flavonoid content is affected by endogenous factors—genotype and agro-environmental conditions. Considerable research has been directed toward understanding the nature of polyphenols in different products and the factors influencing their accumulation. This review examines the impacts of pre- and postharvest factors on onions’ flavonoid content, highlighting how this knowledge may be used to modulate their composition and the potential use of onion by-products.