Determination α-amylase inhibitor activity of methanol extract of coffee leaves using UV-Vis spectrophotometric method and validation

Diabetes mellitus (DM) is a chronic condition caused by the decrease of insulin. Some studies have shown that coffee leaves act as antidiabetic agents. DM can be characterized by high blood glucose levels. To maintain blood glucose levels in normal conditions can be through the inhibition of carbohydrate catabolism such as inhibition of α-amylase. Assay of α-amylase inhibition of coffee leaves extracts in vitro using UV-Vis Spectrophotometric method has been developed to obtain optimum condition. The optimum condition of measurement wavelength, incubation time, substrate concentration, enzyme concentration, and DNS concentration was 540 nm, 15 min, 0.5 mg/mL, 0.5 U/mL, and 4.38 ppm respectively. The inhibitor concentration of acarbose and extract was 25 ppm and 500 ppm. Evaluation of the validation method showed linear result r = 0.9979 (acarbose); r = 0.997 (extract). Detection limit and quantitation limits of acarbose and extract were 4.7377 ppm; 14.2133 ppm and 108.3539 ppm; 325.0618 ppm. RSD (%) of repeatability precision and intermediate precision test for day 1, day 2, and day 3 were 4.899; 4.899; 6.502 and 4.566 for acarbose and 0.394; 0.394; 0.377 and 0.238 for the extract. The accuracy test showed that the IC50 profile decreased as the number of acarbose additions increased. The IC₅₀ of arabica coffee leaves was 286.804 μg/mL.