Catechins are responsible for the astringency of Tea
The astringency of the beverage is due to phenolic constituents known as catechins, which make up a group of compounds that are closely related to tannins. Broadly speaking, tannin is a gallic acid ester of a carbohydrate or phenolic compound and includes compounds derived from wood that are unrelated to tea. Tannins are acidic due to the phenolic hydroxyl groups on the gallic acid moiety. They also act as antioxidants and form complexes or chelates with metals. All of the tannins in tea are catechins, which as a group are hydroxylated flavanols and their gallic acid esters. These compounds make up roughly half of the hot water-soluble material in tea beverages. Some types of catechins are also contained in other plants, but the “tea catechins” are unique to the tea plant. During fermentation process, these catechins undergo phenolic oxidative coupling reactions that yield red-colored catechin dimers such as thearubigins (proanthocyanidins). This latter account for the darker color of the beverages produced from oolong and black tea, and also has physiological activity similar to that of the catechins including antibiotic and immunomodulatory effects. Green tea does not contain appreciable amounts of these catechin dimers.
It is believed that catechins have a wide array of beneficial health effects such as anti-inflammatory, neuroprotective activity, antiviral, antiulcer, antibacterial and antiparasitic effects. Out of many such catechins, widely studied catechin in relation to health affairs is epigallocatechin 3-gallate (EGCG). EGCG constitutes more than 50% of the total flavonoid content in green tea and it is an extremely effective antioxidant. The most studied catechin in relation to health contributing potential is EGCG is a potent antioxidant, and acts to inhibit a number of physiologically important enzymes. There is some evidence that it might have therapeutic applications in the treatment of some types of cancer, chronic fatigue syndrome, endometriosis, neurodegeneration, periapical lesions, regulating the HIV viral load, Sjögren’s syndrome, and spinal muscular atrophy, to name a few.
