2.3. α‐Glucosidase inhibition assay

The assessment of inhibitory activity against α‐glucosidase was based on reported methods (Lordan et al., ²⁰¹³; Tao et al., ²⁰²⁰). α‐Glucosidase and PNPG were dissolved in phosphate buffer solution (0.1 mol/L, pH 6.8). 10 μl of the test sample solution (5mg/ml) was mixed with 40 μl of the α‐glucosidase solution (4 U/ml) and added into a 96‐well cluster plate, incubated at 37°C for 10 min. Then 50 μl of PNPG (2 mmol/L) was added to the reaction mixture. After incubated at 37°C for 1 hr, the reaction was terminated by adding 50 μl of Na₂CO₃ (0.1 mol/L). The absorbance was measured at 405 nm. Acarbose was selected as positive control. The IC₅₀ value (the concentration of inhibitors at which the inhibitory rate of enzyme is 50%) was determined. Correlation coefficients between each active composition in extract and inhibitory rate were calculated using SPSS 22.0 software. The inhibitory rate was calculated as below:

A _sample: Absorbance of test sample + enzyme + PNPG. A _background: Absorbance of test sample without enzyme. A _control: Absorbance of 100% enzyme + PNPG without test sample.