Selenium and flavonoids in selenium-enriched tartary buckwheat roasted grain tea: Their distribution and correlation to antioxidant activity

Abstract

Tartary buckwheat roasted grain tea (TBRGT) is a widely consumed buckwheat product in many countries. We evaluated the distribution of Se and flavonoids to determine the effects of roasting temperature on antioxidant activity of TBRGT, the distribution of Se, and flavonoids were evaluated. Results showed that both the total contents and specific fractions of selenium and flavonoid in TBRGT, TBRGT soup and TBRGT dregs decreased with the increase of roasting temperature. Selenomethionine and Se-polysaccharide were the two main forms of organic selenium in TBRGT while selenocysteine was undetectable. After brewing, the content of selenomethionine in the soup was almost equal to that in dreg. However, Se-polysaccharide was mainly reserved in dreg with few leaching to the soup. Rutin and quercetin were the two main forms of flavonoid in TBRGT. Similar to that of selenomethionine, nearly half of the flavonoids was leached to the soup. We found that antioxidant activity was also decreased aftert roasting processing in all roasted groats, tea soup and dreg. Analysis of correlation revealed that both selenium and flavonoid were significantly correlated with antioxidant activity. Overall, a lower roasting temperature might be more favorable in maintaining the antioxidant activity of TBRGT.