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Bioguided Fraction of Antioxidant Activity of Ethanol Extract from Tartary Buckwheat Bran

¹College of Food Science and Engineering, Northwest A&F University, YangLing, Shaanxi 712100, People's Republic of China. ²Corresponding author. College of Food Science and Engineering, Northwest A&F University, YangLing, Shaanxi People's Republic of China. E-mail: wangmin20050606@163.com ³College of Sciences, Northwest A&F University, YangLing, Shaanxi 712100, People's Republic of China.

This study describes the activity-guided isolation of antioxidant agents from tartary buckwheat bran (TBB). The ethanol crude extract of oil-free TBB was partitioned sequentially into ethyl acetate, n-butanol, and residual aqueous fractions. The ethyl acetate fraction (EAF) had the highest phenolic and flavonoid contents and showed the strongest antioxidant activity. EAF was superior to rutin and inferior to vitamin C (Vc) in DPPH radical scavenging ability, had an advantage over rutin and Vc in ABTS radical scavenging ability, and again surpassed rutin and quercetin in reducing power. Then EAF was subjected to column chromatography, and isolated compounds were identified using nuclear magnetic resonance data by comparing with those reported in the literature. Finally, the bioassay-guided fractionation of the crude ethanol extract of TBB afforded three known compounds (quercetin, p-hydroxybenzoic acid, and daucosterol) responsible for antioxidant activity. p-Hydroxybenzoic acid and daucosterol were isolated from buckwheat grain for the first time. Taken together, establishing of the three pure compounds is of paramount importance to the understanding of antioxidant activity of TBB, and there is an immense potential to process TBB or its EAF into value-added functional foods and beverages.