3.11. α-Glucosidase Inhibitory Activity Assay

The inhibition assay of α-glucosidase was performed using the conditions previously reported with slight modifications [35]. In brief, the solution of α-glucosidase (1 U/mL in 0.1 M phosphate buffer, pH 6.8; 20 μL) was mixed with different concentration of tested compounds (20 μL) in a 96-well microplate. Then, the substrate p-nitrophenyl-α-d-glucopyranoside (p-NPG) (0.375 mM; 40 μL) was added and incubated at 37 °C for 30 min under shaking in the microplate. After adding 0.1 M Na₂CO₃ solution (80 μL), the reaction was terminated, and the absorbance of p-NPG was measured at 405 nm using a 96-well microplate reader. Each experiment was executed in triplicate. Percentage inhibition of each sample was determined using the following equation,

α-Glucosidase inhibition (%) = (A_c − A_t)/A_c × 100, where A_c is the absorbance of the control, and A_t is the absorbance of the test sample. The IC₅₀ values of all tested activities were determined by the liner regression of the percentage of remaining α-glucosidase against the sample concentration.