Antioxidant activity of flavonoids from tartary buckwheat bran

Abstract

In this study, two flavonoid extracts from tartary buckwheat bran were prepared by combining the extraction and hydrolysis processes. The antioxidant activities of the two extracts and three purified flavonoid compounds (rutin, quercetin, and isoquercetin) were investigated by determining their scavenging abilities on three types of free radicals. High-performance liquid chromatography demonstrated that the 85% ethanol extract (named as Extract#1) was mainly composed of rutin and high-pressure hydrolyzate of Extract#1 (designated as Extract#2) contained some quercetin and isoquercetin in addition to rutin. The results from free radicals scavenging assays showed that both extracts and all three compounds displayed a potent ability to scavenge 2,2-diphenyl-1-picrylhydrazl (DPPH) and lesser ability to scavenge hydroxyl and superoxide anion radicals. For DPPH, Extract#2 was comparable to vitamin (Vit) C. The scavenging activity of quercetin was approximately 148% of that of Vit C at a concentration of 5 μg/ml. For superoxide anion radicals, quercetin performed more effective scavenging activity at a concentration of 10 μg/ml, which is approximately 183% of that of Vit C. Overall, Extract#2 exhibited a more effective ability to scavenge these three types of free radicals than Extract#1. Data indicate that high-pressure hydrolysis converted rutin into isoquercetin and quercetin, and this transformation improved the antioxidant capacity of flavonoid extract derived from tartary buckwheat bran.