Classification of green teas from different geographical origins based on micellar electrokinetic chromatography and chemometric techniques

Green tea (GT) has extensively been studied to evaluate and investigate its antioxidant activity and its potential for reducing lifestyle-related diseases. Owing to the beneficial effects on the human health of catechins and to the relationship between the total quality of GT with the content in catechins and caffeine, there is an increasing interest in studying the levels of these compounds in different types of tea samples. Moreover, the quality of tea samples has a great impact on its market value because of the consumers needs, looking for high quality tea products with a clear geographical origin. In this study, a previously developed micellar electrokinetic chromatography (MEKC) method with the addition of hydroxypropyl-β-cyclodextrin was used for electrophoretic profiling of GT samples from different geographical origins. The MEKC method was applied to the quantitation of catechins and xanthines in 92 tea samples of different varieties from Japan and from China, having undergone different storage conditions and manufacturing process. Every sample was characterized by means of 8 variables, namely (+)-catechin, (-)-catechin, (-)-epicatechin, (-)-epigallocatechin, (-)-epigallocatechin gallate, (-)-epigallocatechin gallate, caffeine and theobromine. Unsupervised techniques such as Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) were applied to develop a discriminant model of tea samples in order to not only investigate the relationship between geographical origin and the measured variables but also to evaluate the mutual relationship among all measured variables.