The HPLC profile of crude enzyme-treated onion extract was compared with those from non-treated or inactivated enzyme treated extracts. The peaks at tR 21.0 and 25.8 min (open arrows) were remarkably increased after fermentation, while the peaks at tR 19.0 and 22.7 min (closed arrows), which were the major compounds in control groups, were significantly decreased (Fig. 2). By repeated chromatography, the two decreased compounds were collected and identified as quercetin-3,40-di-O-b-D-glucoside (1) and quercetin-40-O-b-D-glucoside (2) while the two increased compounds were isolated and identified as quercetin-3-O-b-D-glucoside (3) and quercetin (4) based on a comparison of their NMR data with those in the literatures (Fernandez et al., 2005; Fossen et al., 1998). The chemical structures are presented in Fig. 3.