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? ] during the fermentation reactions in black tea. [1] Thearubigins are red in colour and are responsible for much of the staining 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 of theaflavins, another oxidized form of polyphenols.
Thearubigins were first studied by Roberts, E. A. H. in the 1960s [3] by the means of spectroscopy [4] or by fractionation or paper chromatography. [5] They have been identified as proanthocyanidins in 1969. [6] 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. [7] Quantification methods were based on Porter's assay in 1995 [8] and separation made on C18 sorbent cartridges in 1992. [9]
Some new structures like theacitrin have been proposed in 1997 [10] or in 2003 (theasinensins A and B). [11] Further studies made use of MALDI-TOF mass spectrometry in 2004 [12] and other techniques in 2010. [13] [14] It has been shown in 2009 that thearubigins formation in black tea is correlated with catechins depletion. [15]
Flavonoids are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans.
Polyphenols are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of which have been used historically as dyes and for tanning garments.
Chlorogenic acid (CGA) is the ester of caffeic acid and (−)-quinic acid, functioning as an intermediate in lignin biosynthesis. The term "chlorogenic acids" refers to a related polyphenol family of esters, including hydroxycinnamic acids with quinic acid.
Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds. Chemically, they are oligomeric flavonoids. Many are oligomers of catechin and epicatechin and their gallic acid esters. More complex polyphenols, having the same polymeric building block, form the group of tannins.
Procyanidins are members of the proanthocyanidin class of flavonoids. They are oligomeric compounds, formed from catechin and epicatechin molecules. They yield cyanidin when depolymerized under oxidative conditions.
Epigallocatechin gallate (EGCG), also known as epigallocatechin-3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin.
The phenolic content in wine refers to the phenolic compounds—natural phenol and polyphenols—in wine, which include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. These compounds include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the color and mouthfeel of the wine. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
Prodelphinidin is a name for the polymeric tannins composed of gallocatechin. It yields delphinidin during depolymerisation under oxidative conditions.
Procyanidin C2 is a B type proanthocyanidin trimer, a type of condensed tannin.
A type proanthocyanidins are a specific type of proanthocyanidins, which are a class of flavonoid. Proanthocyanidins fall under a wide range of names in the nutritional and scientific vernacular, including oligomeric proanthocyanidins, flavonoids, polyphenols, condensed tannins, and OPCs. Proanthocyanidins were first popularized by French scientist Jacques Masquelier.
Procyanidin A1 is an A type proanthocyanidin dimer.
Procyanidin A2 is an A type proanthocyanidin.
Afzelechin is a flavan-3-ol, a type of flavonoid. It can be found in Bergenia ligulata. It exists as at least 2 major epimers.
Epicatechin gallate (ECG) is a flavan-3-ol, a type of flavonoid, present in green tea. It is also reported in buckwheat and in grape.
Castalagin is an ellagitannin, a type of hydrolyzable tannin, found in oak and chestnut wood and in the stem barks of Anogeissus leiocarpus and Terminalia avicennoides.
Condensed tannins are polymers formed by the condensation of flavans. They do not contain sugar residues.
The phenolic content in tea refers to the phenols and polyphenols, natural plant compounds which are found in tea. These chemical compounds affect the flavor and mouthfeel of tea. Polyphenols in tea include catechins, theaflavins, tannins, and flavonoids.
In biochemistry, naturally occurring phenols refers to phenol functional group that is found in natural products. Phenolic compounds are produced by plants and microorganisms. Organisms sometimes synthesize phenolic compounds in response to ecological pressures such as pathogen and insect attack, UV radiation and wounding. As they are present in food consumed in human diets and in plants used in traditional medicine of several cultures, their role in human health and disease is a subject of research. Some phenols are germicidal and are used in formulating disinfectants.
Catechin-7-O-glucoside is a flavan-3-ol glycoside formed from catechin.
Prunin is a flavanone glycoside found in immature citrus fruits and in tomatoes. Its aglycone form is called naringenin.