Infrared (IR) spectroscopy combined with chemometrics has been developed for simple analysis of flavonoid in the medicinal plant extract. Flavonoid was extracted from medicinal plant leaves by ultrasonication and maceration. IR spectra of selected medicinal plant extract were correlated with flavonoid content using chemometrics. The chemometric method used for calibration analysis was Partial Last Square (PLS) and the methods used for classification analysis were Linear Discriminant Analysis (LDA), Soft Independent Modelling of Class Analogies (SIMCA), and Support Vector Machines (SVM). In this study, the calibration of NIR model that showed best calibration with R 2 and RMSEC value was 0.9916499 and 2.1521897, respectively, while the accuracy of all classification models (LDA, SIMCA, and SVM) was 100%. R 2 and RMSEC of calibration of FTIR model were 0.8653689 and 8.8958149, respectively, while the accuracy of LDA, SIMCA, and SVM was 86.0%, 91.2%, and 77.3%, respectively. PLS and LDA of NIR models were further used to predict unknown flavonoid content in commercial samples. Using these models, the significance of flavonoid content that has been measured by NIR and UV-Vis spectrophotometry was evaluated with paired samples t-test. The flavonoid content that has been measured with both methods gave no significant difference.

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.

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