To date, numerous studies have reported on the
antidiabetic properties of various
plant extracts through inhibition of
carbohydrate-hydrolysing
enzymes. The objective of this research was to evaluate the inhibitory effect of the
hydroxytyrosol and the
oleuropein against α-
amylase and α-
glucosidase. The
hydroxytyrosol was purified from olive leaves. The result shows that the
hydroxytyrosol had the strongest α-
glucosidase inhibitory effect with IC50 values of 150 μM with mild inhibition against α-
amylase. The
enzyme kinetic studies, using Lineweaver-Burk indicated that, in the presence of the
hydroxytyrosol, the Michaelis-Menton constant (Km) remained constant but the maximal velocity (Vmax) decreased, revealing a non-competitive type of inhibition with inhibition constants; Ki for the formation of the
inhibitor-enzyme complex and Kis for the formation of the
inhibitor-enzyme-substrate complex of 104.3 and 150.1 μM, respectively. On the other hand,
oleuropein showedan uncompetitive inhibition. The concentrations used in this work were below cytotoxic levels observed at 400 μM. However, at 600 μM, the
hydroxytyrosol significantly decreased viability of the Caco-2 cells (p < 0.05) and in the case of the
oleuropein, there's an increase in cell number compared to control (p < 0.05). These results suggest that the
hydroxytyrosol and
oleuropein are two potential effective α-
glucosidase inhibitors for management of
postprandial hyperglycemia.