Determination of caffeine, catechins and gallic acid in black tea of different geographical origin

Abstract

We present the results of studying and selectiing optimal conditions for the determination of caffeine, catechins and gallic acid in black tea by the method of micellar electrokinetic chromatography. The choice of analytes is determined by the fact that they form the main consumer qualities of tea and, due to their antioxidant properties, have a positive effect on human health. Optimization of the electrophoretic detemination of seven catechins, caffeine and gallic acid in black tea was carried out using the method of ex­ periment design. Optimized conditions — 25 mM phosphate buffer solution with pH 7.4, containing 30 mM SDS and 5% ethyl alcohol — provided a satisfactory resolution of all electrophoretogram peaks, the analysis time was 25 minutes, and the current in the system did not exceed 120 pA. After the assessment of the metrological characteristics of the proposed method the standard deviation of the determina­tion of analytes did not exceed  15%. The  samples of black tea from Ceylon, Chinese, Assamese, Indian, Kenyan and Krasnodar regions of growth were analyzed, and an array of data on the contents of the analytes under study was formed. Discriminant analysis was used to develop a model and obtain classifica­tion functions for six tea groups from different regions of the world. Proceeding from the obtained classifi­cation functions, a scatter diagram of canonical values was constructed, which showed that the samples of Krasnodar and Chinese tea were localized from all the studied groups. Indian, Assamese and Ceylon teas formed a single area with close to the Chinese tea group. The correctness of the model was checked and revealed the total predictive force about 92%.  It is shown that the content of catechins, gallic acid and caf­feine are suitable markers for the classification of black tea samples from different regions of origin.