Thearubigin

Thearubigins are polymeric polyphenols that are formed during the enzymatic oxidation[1] (called fermentation by the tea trade) of tea leaves. Thearubigins are red in colour. Therefore a black (fully oxidized) tea gives a reddish liquor while a green or white tea gives a much clearer one. The colour of a black tea, however, is affected by many other factors as well, such as the amount of theaflavins, another oxidized form of polyphenols.

It has been believed that theaflavins and thearubigins are important contributors of the taste of a black tea, but recent scientific findings have proven otherwise. More research is still needed to identify the compounds that make up the major components of the taste of a tea. However, it is known that as thearubigins further oxidize if the tea is poorly stored, the taste is adversely affected.

While both the nature and concentration of phenolics in unoxidized teas, such as green teas or white teas, have significant effects on human health, some studies have found thearubigins to have some potency due to their antioxidant properties.

Thearubigins have been first studied by Roberts, E. A. H. in the 1960s[2] by the mean of spectroscopy[3] or by fractionation or paper chromatography[4]. They have been identified as proanthocyanidins in 1969[5]. The thearubigins formation has been studied in an in vitro model in 1983[1].

Thearubigins from black tea extracts have been studied by degradation in 1996[6]. Quantification methods were based on Porter's assay in 1995[7] and separation made on C18 sorbent cartridges in 1992[8].

Some new structures like theacitrin have been proposed in 1997 [9] or in 2003 (theasinensins A and B)[10]. Further studies made use of MALDI-TOF mass spectrometry in 2004[11] and other techniques in 2010[12][13]. It has been shown in 2009 thet thearubigins formation in black tea is correlated with catechins depletion[14].

References

  1. ^ a b Production and HPLC analysis of black tea theaflavins and thearubigins during in vitro oxidation. Alastair Robertson and Derek S. Bendall, Phytochemistry, Volume 22, Issue 4, 1983, Pages 883-887 doi:10.1016/0031-9422(83)85016-X
  2. ^ Economic importance of flavonoid substances; tea fermentation. Roberts, E. A. H., Chem. Flavonoid Compds. (T. A. Geissman, editor. MacMillan Co., New York, N.Y.) (1962) 468-512
  3. ^ Phenolic substances of manufactured tea IX. Spectrophotometric evaluation of tea liquors.Roberts, E. A. H. and Smith, R. F. Journal of the Science of Food and Agriculture (1963), 14(10), 689-700
  4. ^ Phenolic substances of manufactured tea I. Fractionation and paper chromatography of water-soluble substances. Roberts, E. A. H.; Cartwright, R. A.; Oldschool, M., J. Sci. Food Agr. (1957), 8, 72-80
  5. ^ Identification of the Thearubigins as Polymeric Proanthocyanidins. A. G. Brown, W. B. Eyton, A. Holmes and W. D. Ollis, Nature 221, 742 - 744 (22 February 1969), doi:10.1038/221742a0
  6. ^ Elucidation of the partial structure of polymeric thearubigins from black tea by chemical degradation. Ozawa T., Kataoka M., Morikawa K. and Negishi O., Bioscience, biotechnology, and biochemistry, 1996, vol. 60, no12, pp. 2023-2027
  7. ^ Use of Porter's reagents for the characterisation of thearubigins and other non-proanthocyanidins. Powell, C., Clifford, M.N., Opie, S.C. and Gibson, C.L., J-sci-food-agric., May 1995. v. 68, p. 33-38.
  8. ^ Rapid method for measuring thearubigins and theaflavins in black tea using C18 sorbent cartridges. David L Whitehead and Catherine M Temple, Journal of the Science of Food and Agriculture, Volume 58, Issue 1, pages 149–152, 1992 doi:10.1002/jsfa.2740580126
  9. ^ A polyphenolic pigment from black tea. Adrienne L. Davis, John R. Lewis, Ya Cai, Chris Powell, Alan P. Davis, John P. G. Wilkins, Paul Pudney and Mike N. Clifford, Phytochemistry, Volume 46, Issue 8, December 1997, Pages 1397-1402 doi:10.1016/S0031-9422(97)00508-6
  10. ^ Thoughts on thearubigins (Dedicated to the memory of Professor Jeffrey B. Harborne). Edwin Haslam, Phytochemistry, Volume 64, Issue 1, September 2003, Pages 61-73 doi:10.1016/S0031-9422(03)00355-8
  11. ^ Analysis of Theaflavins and Thearubigins from Black Tea Extract by MALDI-TOF Mass Spectrometry. Marie-Claude Menet, Shengmin Sang, Chung S. Yang, Chi-Tang Ho and Robert T. Rosen, J. Agric. Food Chem., 2004, 52 (9), pp 2455–2461 doi:10.1021/jf035427e
  12. ^ Unraveling the structure of the black tea thearubigins. Kuhnert Nikolai, Archives of biochemistry and biophysics, 2010, vol. 501, no1, pp. 37-51
  13. ^ Mass spectrometric characterization of black tea thearubigins leading to an oxidative cascade hypothesis for thearubigin formation. Nikolai Kuhnert, Rapid Communications in Mass Spectrometry, Volume 24, Issue 23, pages 3387–3404, 15 December 2010 doi:10.1002/rcm.4778
  14. ^ Catechins depletion patterns in relation to theaflavin and thearubigins formation. Ngure Francis Muigai, Wanyoko John K., Mahungu Symon M. and Shitandi Anakalo A., Food chemistry, 2009, vol. 115, no1, pp. 8-14