Quercetin in onion (Allium cepa L.) after heat-treatment simulating home preparation
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abstract
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 (sauting, baking, and boiling). Baking and sauting 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. 2004 Elsevier Inc. All rights reserved.