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-quercetin diglucoside (3,4′-Qdg) and 4′-O-quercetin glucoside (4′-Qmg), was examined in five cultivars before and after three cooking treatments (sautéing, baking, and boiling). Baking and sautéing 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 heat stability of the flavonols. Changes in flavonol concentrations as a result of cooking method were consistent across all five cultivars.