Study on the change of flavonoid glycosides to aglycones during the process of steamed bread containing tartary buckwheat flour and antioxidant, α-glucosidase inhibitory activities evaluation in vitro

Tartary buckwheat dough (120 g) was used to produce steamed tartary buckwheat bread (STB). Alterations in antioxidant capacity and α-glucosidase inhibitory activity levels, and the concentrations of various flavonoid compounds, were investigated after each processing stage. It was identified that aglycone (quercetin and kaempferol) levels were increased after dough formation and fermentation stages. These stages were also associated with higher antioxidant capacity and α-glucosidase inhibitory activity. After steaming, flavonoid compound and antioxidant activity levels were slightly decreased in comparison to those observed after dough formation and fermentation steps, although they were higher than in raw flour. To clarify the anti-diabetic potential of individual flavonoid compounds, the antioxidant and α-glucosidase inhibitory activities of four distinct flavonoids were investigated. The results of the present study revealed that aglycones have more potent anti-diabetic effects than their corresponding glycosides, which may explain the change in antioxidant and α-glucosidase inhibitory activities of samples taken after the different processing stages. Correlation analysis also indicated that flavonoids' being in their aglycone form was positively associated with higher antioxidant and α-glucosidase inhibitory activities. Overall, these data suggest that deglycosylation of flavonoids, which occurs during the preparation of STB, contributes to higher hypoglycemic potential in tartary buckwheat bread products.