Quercetin in onion (Allium cepa L.) after heat-treatment simulating home preparation

Quercetin content in onion (Allium cepa L.), represented mainly by 3,4'-O-quereetin diglucoside (3,4'-Qdg) and 4'-O-quereetin glucoside (4'-Qmg), was examined in five cultivars before and after three cooking treatments (sautering, baking, and boiling). Baking and sauteing produced a 7-25% gain in quercetin concentration, while boiling produced an 18% decrease in quercetin concentration. Ratios of 3,4'-Qdg to 4'-Qmg in tissues ranged from 1:1.3 and 1:1.7, and combined the two conjugates represented 89-90% of total flavonol content in treatment and raw control means indicating beat stability of the flavonols. Changes in flavonol concentrations as a result of cooking method were consistent across all five cultivars. (C) 2004 Elsevier Inc. All rights reserved.