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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. 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.
Both the theaflavins but particularly the oligomeric thearubigins are important contributors to the taste of black tea.
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 were first studied by Roberts, E. A. H. in the 1960s by the mean of spectroscopy or by fractionation or paper chromatography. They have been identified as proanthocyanidins in 1969. 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. Quantification methods were based on Porter's assay in 1995 and separation made on C18 sorbent cartridges in 1992.
Some new structures like theacitrin have been proposed in 1997 or in 2003 (theasinensins A and B). Further studies made use of MALDI-TOF mass spectrometry in 2004 and other techniques in 2010. It has been shown in 2009 that thearubigins formation in black tea is correlated with catechins depletion.
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