Abstract: Flos Sophorae Immaturus (FSI) was extracted with chloroform : methanol (1:2) in a ultrasonator, and the extraction was then partitioned with petroleum ether, EtOAc and BuOH successively. Antioxidant activity (AA) of the extract was evaluated by using Schaal method and compared with that of BHT. The BF (n-butanol-soluble fraction) exhibited the highest AA, which was greater than that of BHT. Furthermore, bioactivity-guided chromatographic fractionation was conducted by repeated column chromatography with a silica gel, RP-18, and Sephadex LH-20 to obtain two kinds of pure antioxidant compounds. Their structures were determined by interpretation of the 1D and 2D NMR, as well as mass spectral data. The results demonstrated that quercetin and rutin were the major antioxidative constituents in FSI. The AA of the compounds decreased in the following order: quercetin>rutin>BF> BHT. The AA of phenolic compounds is closely correlated to their chemical structures. In general, the AA of phenolics depends mainly on the number of hydrogen-donating hydroxyl groups on the aromatic ring of the phenolic molecules.

Key words: Flos Sophorae Immaturus, edible oil and fat, antioxidant activity, antioxidative constituent