Aqueous Extracts of Roselle (Hibiscus sabdariffa Linn.) Varieties Inhibit α-Amylase and α-Glucosidase Activities In Vitro

This study sought to investigate the inhibitory effect of aqueous extracts of two varieties (red and white) of Hibiscus sabdariffa (Roselle) calyces on carbohydrate hydrolyzing enzymes (alpha-amylase and alpha-glucosidase), with the aim of providing the possible mechanism for their antidiabetes properties. Aqueous extracts were prepared (1:100 w/v) and the supernatant used for the analysis. The extracts caused inhibition of alpha-amylase and alpha-glucosidase activities in vitro. The IC50 revealed that the red variety (25.2 mu g/mL) exhibited higher alpha-glucosidase inhibitory activity than the white variety (47.4 mu g/mL), while the white variety (90.5 mu g/mL)exhibited higher alpha-amylase inhibitory activity than the red variety (187.9 mu g/mL). However, the alpha-glucosidase inhibitory activities of both calyces were higher than that of their alpha-amylase. In addition, the red variety possessed higher antioxidant capacity as exemplified by the (OH)-O-center dot scavenging abilities, Fe2+ chelating ability, and inhibition of Fe2+-induced pancreatic lipid peroxidation in vitro. The enzyme inhibitory activities and antioxidant properties of the roselle extracts agreed with their phenolic content. Hence, inhibition of alpha-amylase and alpha-glucosidase, coupled with strong antioxidant properties could be the possible underlying mechanism for the antidiabetes properties of H. sabdariffa calyces; however, the red variety appeared to be more potent.