Catechin during processing

In addition to all of the expected enzyme systems present in leaf tissue, fresh tea leaves contain a high level of polyphenol oxidase that catalyzes the oxidation of the catechins by atmospheric oxygen. Tea polyphenol oxidase exists as series of copper-containing (0.32%) isoenzymes. The major component has a molecular weight of about 144,000.54 The enzyme is concentrated in the leaf epidermis.55 Soil copper deficiency is sometimes responsible for inadequate oxidation during processing.56... 

Ananingsih, V.K., Sharma, A., and Zhou, W. 2013. Green tea catechins during food processing and storage A review on stability and detection . Food Research International., 50 469 79. 

Interestingly, the catechin level was the highest in black tea, indicating that the catechin loss is relatively low during the production process of black tea. It was concluded from the results that all three tea types are good sources of these potentially beneficial catechins [180],... 

Finally, Weinges et al. (31, 33) postulated the formation of dimers such as 27 or 28, 29 or 30 directly from catechins without involving 3,4-flavandiols (leucoanthocyanidins). This process has never been demonstrated in fruits directly and specifically not in grapes. Only the proanthocyanin dimers have been positively identified through the formation of catechins and anthocyanidins during acid hydrolysis. Dimer formation proceeds by enzymatic oxidation of two molecules of catechin... 

This complex tannin is formed during the aging process of red wine, whereby the catechin unit originates from the grapes, and the ellagitannin, in this case vescalagin, originates from the oak barrels. 

Green, oolong, black, and pu-erh teas are processed differently during manufacturing. To produce green tea, freshly plucked tea leaves are steamed to prevent fermentation. Catechins are the main compounds in green tea they consist of... 

In addition to the enzymatic pathway of aroma formation, a thermal route also exists. At high temperatures, interactions of amino acids and sngars resnlt in the formation of various aldehydes. After thermal treatment, the tea becomes more tasty and pleasant, and has a better aroma. An essential source of secondary volatiles, formed during tea leaf processing, is oxidative. o-Quinone resulting from the oxidation of catechins can oxidize, besides amino acids and carotenes, unsaturated fatty acids as well. Linoleic and linolenic acids can be converted into hexenal and trans-hex-2-enal, respectively, and in addition, small amounts of other volatile compounds, especially hexanoic acid and trani-hex-2-enoic acid, can be formed from the same acids, respectively. Also the monoterpene alcohols, linalool and geraniol, play an important role in the formation of the aroma of black tea [38]. 

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