The Chemistry and Biochemistry of Tea-Current Status of Our Kknowledge and Still Existing Gaps.
Progress has been made in the past few years with respect to our knowledge of the composition and biochemical reactions of green and black teas.This paper will summarize the current status of our knowledge based on the available literature and own experimental work.This includes analytical methods, data for various constituents, in different types of tea.A database on the flavanol content of green and black teas has been set up using data from labs worldwide.In case of other types of tea, such as white or Oolong teas those data are missing.This is also true for other tea phenolics such as flavonol glycosides,proanthocyanidins, bisflavanols, among others.Important progress has been made in the field of black tea thearubigins (TR).It was shown that one fraction (caffeine precipitate) contains foremost relatively small compounds probably formed by an oxidation pathway starting from four different dimers (theaflavins, theanaphthoquinones, theacitrins and bisflavanols).The oxidative cascade hypothesis was brought up explaining that the TRs are not resolved by chromatography but elute as a broad band.The results are based on sophisticated mass spectrometric techniques.Another approach are model fermentations to get complementary information on the TR.A number of papers have been published on amino acids, especially theanine.Those papers are dealing with the analysis and the possible health benefits of theanine.An international standard is underway for theanine determination.Other areas briefly mentioned are the authenticity of tea and tea products and actions necessary to get closer to possible health claims, e.g.in Europe and the US.Gaps are still data on a number of important tea constituents, such as flavonol glycosides and proanthocyanidins in all types of teas and theaflavin composition in black teas, among others.Moreover quantitative data for TR are not available.It is often a problem that data are generated using non-validated methods.In case the method has really been optimized data should be comparable, but often this is not the case.Tea quality and the content of specific compounds have tried to be correlated since more than 50 years.Currently no concept is in sight that covers the area despite a number of concepts having been developed.
polyphenols flavonoids tea chemistry health effects quality
Ulrich H.Engelhardt
Institute of Food Chemistry, TU Braunschweig, Schleinitzstr.20, D-38106 Braunschweig, Germany
国际会议
International Tea Symposium 2014(ITS 2014)(国际茶叶学术研讨会)
杭州
英文
14-27
2014-09-10（万方平台首次上网日期，不代表论文的发表时间）