Quality Of Green Tea Identification Method

China is the hometown of tea and the cradle of tea culture.There are abundant varieties of tea species in our country including numerous world-renowned teas.Tea is the most popular beverage and the main economic crop of China on account of its beneficial effects to human's health.With the popularization of tea consumption, there are some serious problems such as adulteration,commercial speculation which have adverse effect on the development of tea industry.Therefore,analytical methods to guarantee tea authenticity,based on chemical analysis and sophisticated data analysis procedures,were demanded by consumers and tea producers.The discrepancy of the content of catechins in teas originating from various provenances was evident.According to this thesis,green tea samples originating from different regions were subjected to reveal the natural groups,new analytical methods for analyzing catechins were established and the feasibility of applying chemometric techniques for the classification of green teas based on chemical characteristics was discussed.Chapter 1 reviewed the applications of modern analytical technologies in the quality control of tea in recent years,especially focused on high performance liquid chromatography(HPLC),high performance capillary electrophoresis(HPCE),and gas chromatography(GC).In Chapter 2,a reversed phase high performance liquid chromatography(HPLC) separation coupled with diode array detection(DAD) and electrospray ionization mass spectrometer(ESI-MS) method was developed and optimized for the classification of green teas.Five catechins[epigallocatechin(EGC),epigallocatechin gallate(EGCG),epicatechin(EC),gallocatechin gallate(GCG),epicatechin gallate (ECG)]had been identified and quantified by the HPLC-DAD-ESI-MS-MS method. These compounds were considered as chemical descriptors to define groups of green teas.Chemometric methods including principal component analysis(PCA) and hierarchical cluster analysis(HCA) were applied for the purpose.The results showed that the analyzed green teas were differentiated mainly by provenance;HCA afforded an excellent performance in terms of recognition and prediction abilities.This method was accurate and reproducible,providing a potential approach for authentication of green teas.In Chapter 3,a micellar electrokinetic capillary chromatography method (MEKC) was established for the grouping of green teas,the separation conditions were optimized.Five catechins(EGC,EGCG,EC,GCG,ECG) in samples had been simultaneous analyzed and utilized as chemical descriptors to apply PCA and HCA for grouping.The results indicated that the method was rapid,sensitive and reproducible for the classification of green teas.