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EGCG, Catechins, Antioxidants and Green Tea
Catechins are a type of tannin commonly found in green tea - these chemicals provide both the active antioxidant property of green teas and also the slight astringent taste green teas are noted for.
Black tea also contains catechins, but in smaller amounts because the fermentation process used to make black tea chemically reduces catechins, making them lose their antioxidant properties. The class of chemicals called catechins are powerful, water soluble polyphenols and antioxidants that in can be easily chemically oxidized - making them special as antioxidants in the body.
Several thousand types of catechins occur naturally in the plants. As many as two thousand are known to have a flavon chemical structure and are thus called flavonoids. Catechins are a subclass of flavonoids known for their strong anitoxidant properties.
The most important catechin found in green tea is Epigallocatechin gallate (EGCG). EGCG is the main active and water-soluble component of green tea - there is more EGCG found in green tea than any other type of catechin, and it is known for being the potent antioxidant of the catechin group.
EGCG accounts for 9-13% of green tea in net weight. Because of its peculiar stereochemical structure, EGCG possesses much stronger anti-oxidant activities and plays an important role in preventing cancer and cardiovascular diseases. In addition, new research suggests that EGCG may potently be used as the reversal agent for Multidrug Resistance (MDR) effects often found in cancer treatment, which may improve the sensitivity of the cancer cell to chemotherapy drugs and reduce toxicity associated with chemotherapy on the heart.
Catechins in general are found in high concentrations in green tea because the black tea fermentation process reduces catechins in black tea.
Research aimed at finding the active compounds in green tea have revealed that its protective effects are due chiefly to catechins. Tea contains four main catechin substances: EC, ECG, EGC and EGCG, all of which are inclusively called catechins.
EGCG as an antioxidant is about 25-100 times more potent than vitamins C and E. One cup of green tea provides 10-40 mg of polyphenols and has antioxidant effects greater than a serving of broccoli, spinach, carrots, or strawberries. The high antioxidant activity of green tea makes it beneficial for protecting the body from oxidative damage due to free radicals. Research shows that green tea may help the arterial wall by reducing lipids. Green tea can protect against experimentally induced DNA damage, and slow or halt the initiation and progression of undesirable cell colonies. Studies show evidence that green tea provides immunoprotective qualities, particularly in the case of patients undergoing radiation or chemotherapy. White blood cell count appear to be maintained more effectively in patients consuming green tea compared to non-supplemented patients.
Green tea is manufactured from fresh, unfermented tea leaves; the oxidation of catechins is minimal, and hence they are able to serve as antioxidants. Researchers believe that catechin is effective because it easily sticks to proteins, blocking bacteria from adhering to cell walls and disrupting their ability to destroy them. Viruses have ‘hooks’ on their surfaces and can attach to cell walls. The catechin in green tea prevents viruses from adhering and causing harm. Catechin reacts with toxins created by harmful bacteria (many of which belong to the protein family) and harmful metals such as lead, mercury, chrome, and cadmium.
Tannin in green tea is mostly catechin and is a key component in its taste providing the astringency. The amount of catechin tends to increase as the season progresses. Spring tea (first crop) contains 12-13% catechin (13-17% as tannin) while summer tea (third crop) contains 13-14% (17-21% as tannin). If leaf order is compared, younger leaves include more catechin than mature ones. First leaves contain 14%, second 13%, third 12%, and fourth 12%. This explains why second and third crop summer teas are more astringent while Bancha is less so. Gyokuro green tea, whose leaves are covered during growth, contains less catechin and astringency (10% as tannin) because it gets less sunshine then Sencha.