HPLC-DAD method for simultaneous determination of gallic acid, catechins, and methylxanthines and its application in quantitative analysis and origin identification of green tea

Abstract

The high-performance liquid chromatography coupled with a diode array detector (HPLC-DAD) was optimized for the simultaneous determination of 11 compounds, belonging to polyphenols (gallic acid and seven catechins) and methylxanthines (caffeine, theobromine, and theophylline). The results obtained for all the validation parameters of the HPLC-DAD method showed that the method is sensitive enough for routine analysis with basic chromatographic equipment, thus it has a significant potential to be highly applicable in common laboratory practice. The method was used in the analysis of 60 green tea infusions originating from four tea-producing countries. The dataset contributes to enhancing current data on green tea. The analysis of green tea extracts revealed significant differences depending on the origin of the samples. Linear Discriminant Analysis (LDA) was applied to test the accuracy of identification of the origin of the tea samples, based on the chemical composition of tea with a focus on polyphenolic compounds and methylxanthines analysed in this study. Based on cross-validation results, the model showed 93.75 % accuracy in the classification of green tea originating from Japan, China (Mainland), China (Taiwan) and South Korea.

Keywords: Green tea; HPLC-DAD; Method validation; Methylxanthines; Polyphenols.

Fig. 1

HPLC-DAD chromatograms of standards of methylxanthines and polyphenols measured at 280 nm; A: Standard mixture, B: Tea sample.

Fig. 2

Identification of geographical origin regarding the chemical composition of green tea by LDA. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) Note: A: two-dimensional linear discrimination analysis representing variables and their mutual correlation; GA: gallic acid; GC: (−)-gallocatechin; TBM: theobromine; TEP: theophylline; C: (+)-catechin; CAF: caffeine; EGCG: (−)-epigallocatechin-3-gallate; EC: (−)-epicatechin; GCG: (−)-gallocatechin-3-gallate; ECG: (−)-epicatechin-3-gallate; CG: (−)-catechin-3-gallate; B: LDA plot of identification of geographical origin regarding the chemical composition.