Theaflavins

Theaflavins. One of the more well-defined groups of flavonoid polymers that forms duriag black tea manufacturiag is that of the theaflavins (14). Exhibiting a bright orange-red color in solution, these are important contributors of brightness, a desirable visual attribute used by professional tasters to describe the appearance of tea infusions. 

There are four main theaflavins common to black teas, and a second group of minor theaflavins, including the isotheaflavins (55) and neotheaflavins (57) (Table 5). The total theaflavin concentration in black tea leaves does not usually exceed 2% and can be as low as 0.3%. At most, only 10% of the catechins in tea flush can be accounted for as theaflavins in black tea and the fate of the remaining catechins is less clear. Theaflavins can be readily determined by direct hplc analysis of tea beverages (48,58,59). 

LEE B L and ONG c N (2000) Comparative analysis of tea catechins and theaflavins by high-performance liquid chromatography and capillary electrophoresis , J Chromatog A, 881 (1-2), 439-47. 

MORSE M A, KRESTY L A, STEELE V E, KELLOFF G J, BOONE C W, BALENTINE D A, HARBOWY M E and STONER G D (1997) Effects of theaflavins on N-nitrosomethybenzylamine-induced esophageal tumorigenesis , Nutr Cancer, 29 (1), 7-12. 

NAKANE H (1991) Differential inhibition of HIV-reverse transcriptase and various DNA polymerases by theaflavins , in Proc of Intern Symp on Tea Sci, 26-29 August, 1991, Shizuoka, Japan, 282-6. 

The oxygen-consuming reaction between a quinone derived from a simple catechin and a quinone derived from a gallocatechin results in the formation of a theafiavin. These compounds possess the benztropolone group that is based on a seven-membered ring. Figure 4 illustrates the formation of theaflavins. 

Each of the four theaflavins theoretically are derived from the reactions the quinones of epicatechin or its gallate with those of epigallocatechin or its gallate has been identified in black tea and its structure authenticated.50... 

Theaflavins are orange-red substances that contribute significantly to the desirable appearance of black tea beverage. They can by quantitatively detected in tea by means of their intense absorption spectra.69... 

Theaflavin content increases initially as the oxidation process proceeds but falls off rapidly on prolonged oxidation. The mechanism for its further reaction in the oxidizing leaf system is not definitely known. 

The kinetics of tea extraction have been studied in detail 89 90 Rates for caffeine, theaflavin, and thearubigen extraction have been determined. It has been demonstrated that extraction is not a transport-controlled process. Temperature and time are the rate-limiting variables. 

Maintenance of fermentation temperature at 15°C increases theaflavin levels whereas higher temperatures vary for thearubigen formation. Teas fermented at 15°C bring higher prices than those manufactured at 25 °C or... 

C.79 Higher temperatures also accelerate a decline in polyphenolase activity, whereas peroxidase activity remains high. This favors thearubigen formation at the expense of theaflavin.92... 

Theaflavin levels are enhanced and teas are valued at higher prices when fermentation is carried out at lower (4.5 to 4.8) pH values.93... 

Black tea quality as determined by theaflavin levels is also affected by storage conditions. Low temperatures, low moisture levels, and low oxygen availability retard theaflavin loss. Residual peroxidase activity, which accelerates theaflavin loss on storage, is diminished by acid treatment during fermentation.94... 

Extractable caffeine levels increase on storage, presumably because of decomplexation from theaflavins as the latter decrease. Since caffeine binding with thearubigens is weaker than that with theaflavins, more caffeine may become available.94 An increase in free caffeine may be responsible for decreased value because of the bitterness imparted to the beverage. Caffeine in combination with the normal tea complement of oxidized polyphenolic matter does not exhibit bitterness.95... 

The sensitivity of tea production to research has already been demonstrated by the successful process modifications carried out to increase theaflavin levels and value. There is a limit to what can be accomplished to the confining environment of fermenting leaf. For black instant tea production, the conversion of fresh leaf components to those present in black tea might be better accomplished outside of the leaf. This could allow for more highly directed reaction pathways to bring about the formation of the most desirable end-products. Enzymic and chemical techniques could also be used. 

Roberts, E. A. H. and Smith, R. F., Spectrophotometric measurements of theaflavins and thearubigens in black tea liquors in assessments of quality in teas. Analyst (Bond), 86 94, 1961. 

Spiro, M. and Siddique, S., Kinetics and equilibria of tea infusion. Kinetics of extraction of theaflavins, thearubigens and caffeine from Koonsong Broken Pekoe. J. Sci. Food Agri., 32 1135, 1981. 

Flavonoids exhibit protective action against LDL oxidation. It has been shown [145] that the pretreatment of macrophages and endothelial cells with tea flavonoids such as theaflavin digallate diminished cell-mediated LDL oxidation probably due to the interaction with superoxide and the chelation of iron ions. Quercetin and epicatechin inhibited LDL oxidation catalyzed by mammalian 15-lipoxygenase, and are much more effective antioxidants than ascorbic acid and a-tocopherol [146], Luteolin, rutin, quercetin, and catechin suppressed copper-stimulated LDL oxidation and protected endogenous urate from oxidative degradation [147]. Quercetin was also able to suppress peroxynitrite-induced oxidative modification of LDL [148],... 

The tea plant, Thea sinensis, has provided a desirable beverage for centuries but it is also used as a colorant. Extracts of tea contain a very complex mixture of glycosides of myricetin, quercitin and kaempferol, epicatechin, epigallocatechins, acyl acids and many other polyphenol compounds.33 In black tea, the above compounds may act as precursors to the poorly defined compounds thearubin and theaflavin. 

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