Thearubigin
Encyclopedia
Thearubigins are polymer
ic polyphenols that are formed during the enzymatic oxidation (called fermentation by the tea trade) of tea
leaves. 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.
It has been believed that theaflavins and thearubigins are important contributors of the taste of a black tea, but recent scientific findings have proven otherwise. More research is still needed to identify the compounds that make up the major components of the taste of a tea. However, it is known that as thearubigins further oxidize if the tea is poorly stored, the taste is adversely affected.
While both the nature and concentration of phenolics in unoxidized teas, such as green tea
s or white tea
s, have significant effects on human health, some studies have found thearubigins to have some potency due to their antioxidant
properties.
Thearubigins have been 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 proanthocyanidin
s 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 thet thearubigins formation in black tea is correlated with catechins depletion.
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic polyphenols that are formed during the enzymatic oxidation (called fermentation by the tea trade) of tea
Tea
Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water. The term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world...
leaves. 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.
It has been believed that theaflavins and thearubigins are important contributors of the taste of a black tea, but recent scientific findings have proven otherwise. More research is still needed to identify the compounds that make up the major components of the taste of a tea. However, it is known that as thearubigins further oxidize if the tea is poorly stored, the taste is adversely affected.
While both the nature and concentration of phenolics in unoxidized teas, such as green tea
Green tea
Green tea is made solely from the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures throughout Asia. It has recently become more widespread in the West, where black tea is traditionally...
s or white tea
White tea
White tea is a lightly oxidized tea grown and harvested almost exclusively in China, primarily in the Fujian province.White tea comes from the delicate buds and younger leaves of the Chinese Camellia sinensis plant. These buds and leaves are allowed to wither in natural sunlight before they are...
s, have significant effects on human health, some studies have found thearubigins to have some potency due to their antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
properties.
Thearubigins have been first studied by Roberts, E. A. H. in the 1960s by the mean of spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
or by fractionation
Fractionation
See also: Fractionated spacecraftFractionation is a separation process in which a certain quantity of a mixture is divided up in a number of smaller quantities in which the composition changes according to a gradient. Fractions are collected based on differences in a specific property of the...
or paper chromatography
Paper chromatography
Paper chromatography is an analytical chemistry technique for separating and identifying mixtures that are or can be colored, especially pigments. This can also be used in secondary or primary colors in ink experiments. This method has been largely replaced by thin layer chromatography, however it...
. They have been identified as proanthocyanidin
Proanthocyanidin
Proanthocyanidins, also known as OPCs or condensed tannins, are a subgroup of the flavonoid class of polyphenols...
s 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 thet thearubigins formation in black tea is correlated with catechins depletion.