Thearubigins are polymeric polyphenols that are formed during the enzymatic oxidation and condensation of two gallocatechins (epigallocatechin and epigallocatechin gallate) with the participation of polyphenol oxidases[which?] during the fermentation reactions in black tea.[1] Thearubigins are red in colour and are responsible for much of the staining effect of tea.[2] Therefore, a black (fully oxidized) tea often appears red while a green or white tea has a much clearer appearance. 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.

Thearubigins were first studied by Roberts, E. A. H. in the 1960s[3] by the means of spectroscopy[4] or by fractionation or paper chromatography.[5] They have been identified as proanthocyanidins in 1969.[6] 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.[7] Quantification methods were based on Porter's assay in 1995[8] and separation made on C18 sorbent cartridges in 1992.[9]

Some new structures like theacitrin have been proposed in 1997[10] or in 2003 (theasinensins A and B).[11] Further studies made use of MALDI-TOF mass spectrometry in 2004[12] and other techniques in 2010.[13][14] It has been shown in 2009 that thearubigins formation in black tea is correlated with catechins depletion.[15]

References

  1. ^ a b Robertson, Alastair; Bendall, Derek S. (1983). "Production and HPLC analysis of black tea theaflavins and thearubigins during in vitro oxidation". Phytochemistry. 22 (4): 883–7. doi:10.1016/0031-9422(83)85016-X.
  2. ^ "Which Type of Tea Stains Teeth the Most". 19 June 2012.
  3. ^ Roberts, E. A. H. (1962). "Economic importance of flavonoid substances: tea fermentation". In Geissman, T. A. (ed.). The Chemistry of Flavonoid Compounds. New York: MacMillan. pp. 468–512. OCLC 10460879.
  4. ^ Roberts, E. A. H.; Smith, R. F. (1963). "The phenolic substances of manufactured tea. IX.—the spectrophotometric evaluation of tea liquors". Journal of the Science of Food and Agriculture. 14 (10): 689–700. doi:10.1002/jsfa.2740141002.
  5. ^ Roberts, E. A. H.; Cartwright, R. A.; Oldschool, M. (1957). "The phenolic substances of manufactured tea. I.—Fractionation and paper chromatography of water-soluble substances". Journal of the Science of Food and Agriculture. 8 (2): 72–80. doi:10.1002/jsfa.2740080203.
  6. ^ Brown, A. G.; Eyton, W. B.; Holmes, A.; Ollis, W. D. (1969). "Identification of the Thearubigins as Polymeric Proanthocyanidins". Nature. 221 (5182): 742–4. Bibcode:1969Natur.221..742B. doi:10.1038/221742a0. S2CID 4225363.
  7. ^ Ozawa, Tetsuo; Kataoka, Mari; Morikawa, Keiko; Negishi, Osamu (1996). "Elucidation of the Partial Structure of Polymeric Thearubigins from Black Tea by Chemical Degradation". Bioscience, Biotechnology, and Biochemistry. 60 (12): 2023. doi:10.1271/bbb.60.2023. INIST 2576463.
  8. ^ Powell, Christopher; Clifford, Michael N; Opie, Shaun C; Gibson, Colin L (1995). "Use of Porter's reagents for the characterisation of thearubigins and other non-proanthocyanidins". Journal of the Science of Food and Agriculture. 68 (1): 33–8. doi:10.1002/jsfa.2740680106.
  9. ^ Whitehead, David L; Temple, Catherine M (1992). "Rapid method for measuring thearubigins and theaflavins in black tea using C18 sorbent cartridges". Journal of the Science of Food and Agriculture. 58 (1): 149–52. doi:10.1002/jsfa.2740580126.
  10. ^ Davis, Adrienne L.; Lewis, John R.; Cai, Ya; Powell, Chris; Davis, Alan P.; Wilkins, John P.G.; Pudney, Paul; Clifford, Mike N. (1997). "A polyphenolic pigment from black tea". Phytochemistry. 46 (8): 1397. doi:10.1016/S0031-9422(97)00508-6.
  11. ^ Haslam, Edwin (2003). "Thoughts on thearubigins". Phytochemistry. 64 (1): 61–73. doi:10.1016/S0031-9422(03)00355-8. PMID 12946406.
  12. ^ Menet, Marie-Claude; Sang, Shengmin; Yang, Chung S.; Ho, Chi-Tang; Rosen, Robert T. (2004). "Analysis of Theaflavins and Thearubigins from Black Tea Extract by MALDI-TOF Mass Spectrometry". Journal of Agricultural and Food Chemistry. 52 (9): 2455–61. doi:10.1021/jf035427e. PMID 15113141.
  13. ^ Kuhnert, Nikolai (2010). "Unraveling the structure of the black tea thearubigins". Archives of Biochemistry and Biophysics. 501 (1): 37–51. doi:10.1016/j.abb.2010.04.013. PMID 20430006. INIST 23205455.
  14. ^ Kuhnert, Nikolai; Drynan, J. Warren; Obuchowicz, Jaczek; Clifford, Michael N.; Witt, Matthias (2010). "Mass spectrometric characterization of black tea thearubigins leading to an oxidative cascade hypothesis for thearubigin formation". Rapid Communications in Mass Spectrometry. 24 (23): 3387–404. Bibcode:2010RCMS...24.3387K. doi:10.1002/rcm.4778. PMID 21072794.
  15. ^ Ngure, Francis Muigai; Wanyoko, John K.; Mahungu, Symon M.; Shitandi, Anakalo A. (2009). "Catechins depletion patterns in relation to theaflavin and thearubigins formation". Food Chemistry. 115 (1): 8–14. doi:10.1016/j.foodchem.2008.10.006. INIST 21274489.
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