Catechin esters

Table 4.3) — polymers of catechin and catechin esters criteria and included in the database. 

The initial oxidation of the flavanol components of fresh leaf to quinone structures through the mediation of tea polyphenol oxidase is the essential driving force in the production of black tea. While each of the catechins is oxidizable by this route, epigallocatechin and its galloyl ester are preferentially oxidized.68 Subsequent reactions of the flavonoid substances are largely nonenzymic. 

Flavanols/Procyanidins Catechin, epicatechin, and their gallic acid esters Apples, grapes, plums, pears, mangoes, okra, peaches, Swiss chard, berry fruits and vegetables in general,... 

Building blocks Gallic acid, galloyl ester, ester-linked with glucose Flavanoid units (Procyanidins), catechin... 

Catechins are widely distributed in plants however, they are rich only in tea leaves, where catechins may constitute up to 25% of dry leaf weight. Catechins of green tea include the flavanols epicatechin, epigallocatechin, and their gallate esters (Table 14). 

For the red wines (82-84), which were injected directly into the HPLC without sample preparation, a ternary-gradient system using aqueous acetic acid (1% and 5% or 6%), and acidified acetonitrile (acetonitrile-acetic acid-water, 30 5 6) was used for cinnamic acid derivatives, catechins, flavonols, flavonol glycosides, and proanthocyanidins. Due to the large number of peaks, the gradient was extended to 150 min for the resolution of many peaks of important phenolics. This direct injection method was able to separate phenolic acids and esters, catechins, proanthocyanidins, flavonols, flavonol glycosides, and other compounds (such as tyrosol, and rrans-resveratrol) in wine in a single analysis. However, use of acetic acid did not permit the detector (PDA) to be used to record the UV spectra of phenolics below 240 nm (84). 

Catechins (1.41) can also be found as gallic acid esters that are esterified at the 3 hydroxyl group. Note the difference between the gallic acid ester of catechin (1.41) and gallocatechin (1.40). 

Complex tannins are defined as tannins in which a catechin unit (1.39) is bound glycosidically to either a gallotannin or an ellagitannin unit. As the name implies, the structure of these compounds can be very complex. An example is Acutissimin A (1.99). This is a flavogallonyl unit bound glucosidically to Cl, with an additional three hydrolyzable ester bonds to a D-glucose-derived open-chain polyol. 

Inhibitory Action of Green Tea Catechins, Gallate Esters, and Other... 

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