Thearubigins arepolymericpolyphenols that are formed during theenzymatic oxidation and condensation of two gallocatechins (epigallocatechin andepigallocatechin gallate) with the participation ofpolyphenol oxidases[which?] during thefermentation reactions inblack tea.[1] Thearubigins are red in colour and are responsible for much of thestaining 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 oftheaflavins, another oxidized form of polyphenols.
Thearubigins were first studied by Roberts, E. A. H. in the 1960s[3] by the means ofspectroscopy[4] or byfractionation orpaper chromatography.[5] They have been identified asproanthocyanidins in 1969.[6] Thearubigin formation was studied in an in vitro model in 1983, showing that the in vitro model used was a possible proxy for in vivo oxidation, which would allow further study under controlled conditions.[1]
The structure of thearubigins was studied by degradation in 1996, showing that "thearubigins are ... polymers offlavan-3-ol and flavan-3-ol gallates".[7] Quantification methods were based on Porter's assay in 1995[8] and separation made on C18 sorbent cartridges in 1992.[9]
New structures liketheacitrin andtheasinensins A andB were proposed in 1997 and in 2003, respectively.[10][11] Further studies made use of MALDI-TOF mass spectrometry in 2004[12] and other techniques in 2010.[13][14] It was shown in 2009 that thearubigin formation in black tea is correlated withcatechin depletion.[15]
^abRobertson, 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.
^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.OCLC10460879.
^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.
^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.
^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.INIST2576463.
^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.
^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.
^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.
^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.PMID15113141.
^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.PMID21072794.
^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.INIST21274489.
