thearubigin
{{Short description|Organic polymers group}}
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|date=May 2015}} during the fermentation reactions in black tea.{{cite journal |doi=10.1016/0031-9422(83)85016-X |title=Production and HPLC analysis of black tea theaflavins and thearubigins during in vitro oxidation |year=1983 |last1=Robertson |first1=Alastair |last2=Bendall |first2=Derek S. |journal=Phytochemistry |volume=22 |issue=4 |pages=883–7}} Thearubigins are red in colour and are responsible for much of the staining effect of tea.{{Cite web|url=http://www.freysmiles.com/blog/view/which-type-of-tea-stains-teeth-the-most|title=Which Type of Tea Stains Teeth the Most|date=19 June 2012}} 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{{cite book |chapter=Economic importance of flavonoid substances: tea fermentation |last1=Roberts |first1=E. A. H. |title=The Chemistry of Flavonoid Compounds |editor1-last=Geissman |editor1-first=T. A. |publisher=MacMillan |location=New York |year=1962 |pages=468–512 |oclc=10460879}} by the means of spectroscopy{{cite journal |doi=10.1002/jsfa.2740141002 |title=The phenolic substances of manufactured tea. IX.—the spectrophotometric evaluation of tea liquors |year=1963 |last1=Roberts |first1=E. A. H. |last2=Smith |first2=R. F. |journal=Journal of the Science of Food and Agriculture |volume=14 |issue=10 |pages=689–700}} or by fractionation or paper chromatography.{{cite journal |doi=10.1002/jsfa.2740080203 |title=The phenolic substances of manufactured tea. I.—Fractionation and paper chromatography of water-soluble substances |year=1957 |last1=Roberts |first1=E. A. H. |last2=Cartwright |first2=R. A. |last3=Oldschool |first3=M. |journal=Journal of the Science of Food and Agriculture |volume=8 |issue=2 |pages=72–80}} They have been identified as proanthocyanidins in 1969.{{cite journal |doi=10.1038/221742a0 |title=Identification of the Thearubigins as Polymeric Proanthocyanidins |year=1969 |last1=Brown |first1=A. G. |last2=Eyton |first2=W. B. |last3=Holmes |first3=A. |last4=Ollis |first4=W. D. |journal=Nature |volume=221 |issue=5182 |pages=742–4|bibcode=1969Natur.221..742B |s2cid=4225363 }} The thearubigins formation has been studied in an in vitro model in 1983.
Thearubigins from black tea extracts have been studied by degradation in 1996.{{cite journal |id={{INIST|2576463}} |doi=10.1271/bbb.60.2023 |title=Elucidation of the Partial Structure of Polymeric Thearubigins from Black Tea by Chemical Degradation |year=1996 |last1=Ozawa |first1=Tetsuo |last2=Kataoka |first2=Mari |last3=Morikawa |first3=Keiko |last4=Negishi |first4=Osamu |journal=Bioscience, Biotechnology, and Biochemistry |volume=60 |issue=12 |pages=2023}} Quantification methods were based on Porter's assay in 1995{{cite journal |doi=10.1002/jsfa.2740680106 |title=Use of Porter's reagents for the characterisation of thearubigins and other non-proanthocyanidins |year=1995 |last1=Powell |first1=Christopher |last2=Clifford |first2=Michael N |last3=Opie |first3=Shaun C |last4=Gibson |first4=Colin L |journal=Journal of the Science of Food and Agriculture |volume=68 |issue=1 |pages=33–8}} and separation made on C18 sorbent cartridges in 1992.{{cite journal |doi=10.1002/jsfa.2740580126 |title=Rapid method for measuring thearubigins and theaflavins in black tea using C18 sorbent cartridges |year=1992 |last1=Whitehead |first1=David L |last2=Temple |first2=Catherine M |journal=Journal of the Science of Food and Agriculture |volume=58 |issue=1 |pages=149–52}}
Some new structures like theacitrin have been proposed in 1997{{cite journal |doi=10.1016/S0031-9422(97)00508-6 |title=A polyphenolic pigment from black tea |year=1997 |last1=Davis |first1=Adrienne L. |last2=Lewis |first2=John R. |last3=Cai |first3=Ya |last4=Powell |first4=Chris |last5=Davis |first5=Alan P. |last6=Wilkins |first6=John P.G. |last7=Pudney |first7=Paul |last8=Clifford |first8=Mike N. |journal=Phytochemistry |volume=46 |issue=8 |pages=1397}} or in 2003 (theasinensins A and B).{{cite journal |doi=10.1016/S0031-9422(03)00355-8 |title=Thoughts on thearubigins |year=2003 |last1=Haslam |first1=Edwin |journal=Phytochemistry |volume=64 |pages=61–73 |pmid=12946406 |issue=1}} Further studies made use of MALDI-TOF mass spectrometry in 2004{{cite journal |doi=10.1021/jf035427e |title=Analysis of Theaflavins and Thearubigins from Black Tea Extract by MALDI-TOF Mass Spectrometry |year=2004 |last1=Menet |first1=Marie-Claude |last2=Sang |first2=Shengmin |last3=Yang |first3=Chung S. |last4=Ho |first4=Chi-Tang |last5=Rosen |first5=Robert T. |journal=Journal of Agricultural and Food Chemistry |volume=52 |issue=9 |pages=2455–61 |pmid=15113141}} and other techniques in 2010.{{cite journal |id={{INIST|23205455}} |doi=10.1016/j.abb.2010.04.013 |title=Unraveling the structure of the black tea thearubigins |year=2010 |last1=Kuhnert |first1=Nikolai |journal=Archives of Biochemistry and Biophysics |volume=501 |pages=37–51 |pmid=20430006 |issue=1}}{{cite journal |doi=10.1002/rcm.4778 |title=Mass spectrometric characterization of black tea thearubigins leading to an oxidative cascade hypothesis for thearubigin formation |year=2010 |last1=Kuhnert |first1=Nikolai |last2=Drynan |first2=J. Warren |last3=Obuchowicz |first3=Jaczek |last4=Clifford |first4=Michael N. |last5=Witt |first5=Matthias |journal=Rapid Communications in Mass Spectrometry |volume=24 |issue=23 |pages=3387–404 |pmid=21072794|bibcode=2010RCMS...24.3387K }} It has been shown in 2009 that thearubigins formation in black tea is correlated with catechins depletion.{{cite journal |id={{INIST|21274489}} |doi=10.1016/j.foodchem.2008.10.006 |title=Catechins depletion patterns in relation to theaflavin and thearubigins formation |year=2009 |last1=Ngure |first1=Francis Muigai |last2=Wanyoko |first2=John K. |last3=Mahungu |first3=Symon M. |last4=Shitandi |first4=Anakalo A. |journal=Food Chemistry |volume=115 |issue=1 |pages=8–14}}