Radical scavenging compounds in onion skin

Two major flavonols (F-I and F-II) in onion skin were isolated. According to the ultraviolet-visible absorption spectra, F-I and F-II fractions were thought to be 3,5,7,3'-OH and 3 (5),7,3',4'-OH of flavonol, respectively. After acid hydrolysis of the two fractions, F-I was found to consist of quercetin and glucose, but F-II only contained quercetin. F-I and F-II were confirmed by fast atom bombardment as quercetin 4'-glucoside and quercetin, respectively. The F-I and F-II fractions exhibited potent radical scavenging activity against DPPH, superoxide anion (O2 .(-)) and hydroxyl (. OH) radicals. (C) 2000 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.