Theaflavin formation

FIGURE 15.2. A proposed mechanism of theaflavins formation from catechin oxidation. 

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. 

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... 

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. 

The various chemical processes influencing the colour formation in tea have been vigorously investigated. The self-association of black tea polyphenol theaflavin and its com-plexation with caffeine [175], and the role of epicatechin quinone in the synthesis and degradation of theaflavin [176] have been studied in detail. 

Another experiment was carried out by adjusting the pH of the water and then they were employed for the preparation of the tea infusion. HPLC resulted in the separation of more than 50 components in the broken black tea infusion as demonstrated in Fig. 2.69. Unfortunately, the majority of peaks have not been identified and the chromatographic profiles only indicate the presence of many compounds in the infusions. Some results are presented in Table 2.66. The measurement indicated that theaflavins and tea catechins play a decisive role in the formation of cream particles and tea colour [184],... 

During fermentation in the preparation of black tea, oxidative polymerization of flavanols occurs with the formation of theaflavin, theaflavingallates, thearubigins, and epitheaflavic acid [44]. 

Green tea has been fonnd to possess a high antioxidant activity owing to its high content of catechins. Processes nsed in the manufacture of black and pu-erh teas are known to decrease the levels of monomeric catechins to a much greater extent of polymerization that leads to the formation of theaflavins and thearubigins. The production and consnmption of partially fermented oolong tea and drastically fermented pu-erh tea are confined to China. 

Considerable interest has developed in the past decade in unraveling the beneficial health effects of tea, particnlarly in its polyphenolic components and its antioxidant activity. Catechins, theaflavins, and thearnbigins are three important gronps of polyphenols present in tea. The formation mechanism of these componnds dnring tea processing as well as their respective biological activities are of great importance and of scientific and commercial interest. 

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