Onions are rich in chemical groups with recognized benefits for human health: flavonoids and sulfoxides of alqu (in) il cysteine (ACSO). There are two subgroups of flavonoids in onions, anthocyanins, responsible for the red / purple color of some varieties and quercetin and its derivatives responsible for the yellow and brown skin of many other varieties. ACSOs are the precursors of flavor which, when cleaved by the enzyme alliinase, generate the characteristic smell and flavor of onions. The subsequent products are a complex mixture of compounds including thiosulfinates, thiosulfonates, mono-, di- and trisulfides.
In this review, researchers from Horticulture Research International (UK) have reported evidence from clinical data obtained using onion extracts and their health benefits including anti-cancer properties, anti-platelet activity, anti-thrombotic activity, anti-asthma effects, and antibiotics.
Onions—A global benefit to health. Gareth Griffiths, Laurence Trueman, Timothy Crowther, Brian Thomas y Brian Smith. J Agric Food Chem. 2007; 55(25):10067-80. doi: 10.1021/jf0712503.