3.6. α-Glucosidase Inhibiting Assay

The α-glucosidase inhibition assay was performed using a spectrophotometric method [19]. α-Glucosidase from Saccharomyces cerevisiae was dissolved in phosphate buffer (pH 6.8) containing BSA (0.2%) up to 0.5 U/mL concentration. Solutions (10 μL) of sample in phosphate buffer (pH 6.8) of varying concentrations (10–1000 μg/mL) were premixed with 490 μL of phosphate buffer (pH 6.8) and 250 μL 5 mM p-nitrophenyl-α-d-glucopyranoside. After preincubating at 37 °C for 5 min, 250 μL of α-glucosidase (0.4 U/mL) was added and incubated at 37 °C for 15 min. The reaction was terminated by the addition of 200 μL Na₂CO₃ (200 mM). Absorbance was measured at 400 nm. A 2% solution of acarbose was used as a positive control (PC), and water was used as a negative control (NC). The ability to inhibit glucosidase was calculated using the following equation:

where A₄₀₀^NC is the absorbance of the negative control, A₄₀₀^PC is the absorbance of the positive control and A₄₀₀^Sample is the absorbance of the sample solution. The IC₅₀ value is the effective concentration at which α-glucosidase activity was inhibited by 50%. Values are expressed as mean from five independent experiments.