An isocratic HPLC procedure was developed for simultaneous determination of six catechins, gallic acid, and three methylxanthines in tea water extract. A baseline separation was achieved on a Cosmosil C18-MS packed column with a solvent mixture of methanol/doubly distilled water/formic acid (19.5:80.2:0.3, v/v/v) as mobile phase. A gradient HPLC procedure was also provided for the separation of these tea components. The contents of catechins, gallic acid, and methylxanthines have been measured in infusions of a range of green tea, oolong tea, and pu-erh tea products sold and consumed in the China, Japan, and Taiwan. When 15 Chinese green tea and 13 Japanese green tea products were analyzed by the HPLC method, the mean levels of the total catechins, (-)-epigallocatechin 3-gallate, (+)-catechin, and caffeine were found to be very similar in these two groups, but other minor catechins such as (-)-epigallocatechin, (-)-epicatechin, and (-)-gallocatechin 3-gallate were found to be higher in Japanese green tea products, whereas (-)-epicatechin 3-gallate, gallic acid, theophylline, and theobromine were found to be higher in Chinese green tea products. Oolong tea products possessed lower levels of catechins, whereas pu-erh tea products contained negligible amounts of these constituents. The new HPLC method is rapid, reliable, and reproducible and should be highly recommended to tea industries for routine analysis of commercial tea samples.

The polyphenols in various parts of the tea plant used in manufacture of tea products (young leaves, old leaves, and stem) were analyzed by HPLC. The young leaves (apical bud and the two youngest leaves) were found to be richer (2.7-fold) in polyphenols than old leaves (from the tenth to the fifth leaf). Also, the tea polyphenols were found to be higher (1.4-fold) in summer than in spring. Ten different types of commercial tea (manufactured tea), including unfermented, semifermented, and fermented tea, were analyzed for their polyphenol compounds, and it was found that both yields of solids in tea water extracts (TWEs) and the amount of (-)-epigallocatechin 3-gallate (EGCG) in these products varied with different tea leaves and processing methods. Longjing tea (unfermented green tea) contained the highest concentration of EGCG and polyphenols, whereas Assam black tea (most fermented) contained the least. Longjing TWEs showed strong inhibitory effect on DNA synthesis in A-431 tumor cells. We also found that green tea polyphenols (GTPs) and EGCG strongly inhibited tumor cell DNA synthesis and peroxyl-radical generation. The evidence suggests that the strong antioxidative and antiproliferative activities of Longjing TWEs and GTPs are mainly due to the higher contents of tea polyphenols. EGCG (the major component of GTPs) showed strong inhibitory action on the growth of immortalized cells (NIH3T3) and tumor cells (S-180II) but almost no effect on the growth of normal cells (C3H10T1/2).

A direct qualitative and quantitative determination of the glycosides of tea aroma compounds at the four stages of the oolong tea manufacturing process (plucking, solar withering, indoor withering, and oolong tea product) was carried out by a capillary gas chromatographic-mass spectrometric analysis after trifluoroacetyl derivatization of the glycosidic fractions. Sixteen glucosides and primeverosides were identified and quantified in cv. Chin-shin-oolong and cv. Chinhsuan-oolong. A comparison of the glycosides in dried fresh leaves between the two cultivars showed significant differences. During the manufacturing process, the amounts of most of these glycosides increased from the solar-withering stage, reaching the highest level at the final stage of oolong tea production. It was noted that no glycoside decreased in its content during the manufacturing process, this being quite different from the manufacture of black tea. In addition, the contents of these alcoholic aroma compounds in the free aroma concentrate from each cultivar remained almost unchanged or slightly decreased, and they constituted only about 12 and 17% in amount of the whole oolong tea aroma compounds. However, jasmine lactone and indole were markedly higher in the final oolong tea products.

In this animal study, Wistar rats were fed 2.5% green tea (longjing) leaves, for 27 and 63 weeks; the changes of GOT, GPT, γ-GT, and creatinine were not significant in the treated group as compared with the control. These results suggested that long-term feeding of green tea leaves was not toxic to the liver or kidney. Serum total cholesterol, triglyceride, and LDL-C were decreased in the tested group. Interestingly, the dietary intakes of the two groups were approximately the same, but the body weights of the tea-fed group were decreased 10−18% compared with those of the control. The activities of antioxidant enzymes (SOD and catalase) and phase II enzyme (GST) and glutathione concentration in the liver of Wistar rats were significantly higher in the treated group. The biological significance of these results can be implicated in relation to the hypolipidemic effect as well as the cancer chemopreventive action of green tea. Keywords: Longjing tea; GST; HDL-C; hypolipidemic; LDL-C; phase II enzyme; SOD

No abstract