Effects of different polyphenol-rich herbal teas on reducing predicted glycemic index

Abstract

The purpose of this study was to investigate the effects of different polyphenol-rich herbal teas on reducing the in vitro starch digestibility of white bread and evaluation of predicted glycemic indexes. Generally, except for the goji berry treatment, all herbal teas reduced the starch digestibility and predicted glycemic index of white bread. Compared to untreated white bread, the rapidly digestible starch levels were decreased by 10% and 12% in the turmeric tea treatment. In addition, hydrolysis indexes were decreased by 12% and 10% in the black tea treatment compared to untreated white bread. The turmeric treatment on white bread reduced the predicted glycemic index more than other teas. It is thought that the curcumin in turmeric has more inhibitory effects on α-amylase activity than other teas. We also demonstrated that dietary polyphenols such as anthocyanins and catechins found in herbal teas might reduce starch digestion by inhibiting α-amylase and α-glucosidase thereby lowering the glycemic index of foods.

Practical Application: When we evaluate the effects of polyphenol-rich herbal teas treatment on the quality of starch fractions, overall, the black tea, cinnamon, goji berry, blueberry, cranberry, and rosehip were increased the starch fractions quality. We revealed that dietary polyphenols such as anthocyanins and catechins found in herbal teas could reduce the starch digestion by the inhibition of α-amylase and α- glucosidase resulting in lowering of the GI of foodstuffs. Overall, consumption of the herbal teas made of colored berries, turmeric, and cinnamon may contribute to lowering the glycemic index of foods.