Thearubigin

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 during the fermentation reactions in black tea.[1] Thearubigins are red in colour. 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[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 that thearubigins formation in black tea is correlated with catechins depletion.[14]

References

  1. ↑ 1.0 1.1 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. ↑ Roberts, E. A. H. (1962). "Economic importance of flavonoid substances: tea fermentation". In Geissman, T. A. The Chemistry of Flavonoid Compounds. New York: MacMillan. pp. 468–512. OCLC 10460879.
  3. ↑ 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.
  4. ↑ 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.
  5. ↑ Brown, A. G.; Eyton, W. B.; Holmes, A.; Ollis, W. D. (1969). "Identification of the Thearubigins as Polymeric Proanthocyanidins". Nature 221 (5182): 742–4. doi:10.1038/221742a0.
  6. ↑ 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.
  7. ↑ 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.
  8. ↑ 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.
  9. ↑ 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.
  10. ↑ Haslam, Edwin (2003). "Thoughts on thearubigins". Phytochemistry 64 (1): 61–73. doi:10.1016/S0031-9422(03)00355-8. PMID 12946406.
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ 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. doi:10.1002/rcm.4778. PMID 21072794.
  14. ↑ 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.