Major Secondary Metabolites And Glycosidic Aroma Precursors From Green Tea Aqueous Extracts

Depending on different manufacturing processes, tea can be classified intothree major types: non-fermented tea, semi-fermented tea, and fermented tea.Green tea is a typical non-fermented tea, the manufacture processing stepsinclude plucking the fresh leaf, rapid enzyme inactivation by steaming or panfiring, rolling, and high temperature air drying. Tea composition varies withclimate, season, tea variety, and processing. The characteristic components mainlyincluding xanthine alkaloids, tannins, phenolic substances, catechins, flavonoidsand polymerized flavanols. Green tea produced by drying and steaming the freshleaves to stop the enzymatic oxidases. By this way, non enzymatic oxidationoccurs on polyphenols and other main characteristic components in the tea, andkept much more original components of tea fresh leaf, especially polyphenolsand chlorophyll et al. Therefore, green tea contains much abundant secondarymetabolites. It has been revealed that green tea contains more than700kinds oforganic compounds and15kinds of inorganic minerals, which not only gives thetea itself an unique color, flavor and quality, but also shows much more humanhealthy benefits, for example anti-ageing, cancer-prevention, anti-carcinogenic,sterilization, anti-inflammatory, anti-hyperlipidemics, weight control and otherspecial effects. In order to get high-purity standard compounds and establish acompound library of main secondary metabolites of green tea aqueous extracts,we studied the major secondary metabolites from green tea aqueous extracts. Themajor results obtained of this paper list as following:1. Amberlite XAD-2, silica gel and sephadex LH-20column chromatographywere used to separate and purify the main secondary metabolites from green teaaqueous extracts. On the basis of mass spectrometry and nuclear magneticresonance technologies, the chemical structures of the purified compounds wereelucidated as follows: caffeine(1,3,7-trialkylxanthines)(1), catechin gallate(2),epicatechin(3),3,5-dihydroxy-4-methoxy-benzoic acid(4), kaempferol-3-glucoside(5),gallocatechin gallate(6), catechin(7), gallic acid(8). These results will contribute toestablish the compound library of main secondary metabolites of green teaaqueous extracts and following individual component activity investigations.2. A preliminary separation of glycosidic aroma precursors in green tea havebeen performed. Boilling water was used to extract glycosides from green tea andpolyvinylpolypyrrolidone was used to deposit tea polyphenols from glycosides extraction. The extracts of glycosides was separated by macro-porous resincolumn chromatography. We use gas chromatography to analysis enzymaticsamples of different concentrations of methanol eluts of column chromatographyand definitude the enrichment part of glycosidic aroma precursors. The results ofgas chromatographic analysis shows that macro-porous resin columnchromatography is an effective separation method for glycosides, and theenzymatic released volatile components was mainly existed in40%and60%methano eluts. Geraniol was mainly in60%fraction. cis-3-hexenol, phenylethylalcohol and methyl salicylate were both detected in10%,20%and40%fractions, butmainly enriched in the40%fraction; linalool and geraniol were concentrated in40%,60%ad80%fraction; nerolidol3,7,11-Trimethyl-1,6,10-dodecatrien-3-ol wasonly detected in80%fraction. However nerol was not detected in any fractions, thepossible reason was the limit content or the shortage of extraction methods. Inaddition, the results of GC-MS chromatography analysis of enzymatic samplesshows that there were volatiles of linalool oxide I (cis, furanoid) and linalool oxide II(trans, furanoid), β-myrcene, octatriene, neral, and1-nonanol in samples.