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6410252 
Journal Article 
Antibacterial and antioxidant activities of quercetin oxidation products from yellow onion (Allium cepa) skin 
Ramos, FA; Takaishi, Y; Shirotori, M; Kawaguchi, Y; Tsuchiya, K; Shibata, H; Higuti, T; Tadokoro, T; Takeuchi, M 
2006 
Yes 
Journal of Agricultural and Food Chemistry
ISSN: 0021-8561
EISSN: 1520-5118 
54 
10 
3551-3557 
English 
19127724 
Four new quercetin-derived oxidation products (1-4) and lunularin-4-O-beta-D-glucoside (5) were isolated from a water extract of onion (Allium cepa) skin, together with 17 other known compounds. Antibacterial assays for the isolated compounds showed that 2-(3,4-dihydroxyphenyl)-4,6-dihydroxy-2-methoxybenzofuran-3-one (1) presented selective activity against Helicobacter pylori strains and 3-(quercetin-8-yl)-2,3-epoxyflavanone (4) showed antibacterial activity against MRSA and H. pylori strains at the same time that it increased susceptibility of MRSA to beta-lactams. Evaluation of antioxidant activity against DPPH for the isolated compounds showed that the new derivative compounds (1-4) and 2,5,7,3',4'-pentahydroxy-3,4-flavandione (6) are more active than quercetin. 
; Skin; Antioxidants; Antibacterial activity; Drug resistance; beta -Lactam antibiotics; Oxidation; Quercetin; Helicobacter pylori; Allium cepa/