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Tuesday, 11 April 2006 |
Both green tea and black tea are derived from the same plant, the tea plant (Camellia sinensis). The parts used are the leaf bud and the two adjacent young leaves together with the stem, broken between the second and third leaf. Older leaves are considered inferior in quality. Green tea is produced by lightly steaming the fresh-cut leaf, while to produce black tea the leaves are allowed to oxidize. During oxidation, enzymes present in the tea convert polyphenols, which possess outstanding therapeutic action, to compounds with much less activity. With green tea, oxidation is not allowed to take place because the steaming process inactivates these enzymes. Green tea is very high in polyphenols with potent antioxidant and anticancer properties. The chemical composition of green tea varies with climate, season, horticultural practices, and age of the leaf (position of the leaf on the harvested shoot). The major components of interest are the polyphenols. the term polyphenol denotes the presence of multiple phenolic rings. The major polyphenols in green tea are flavonoids (e.g., catechin, epicatechin, epicatechin gallate and proanthocyanidins). Epigallocatechin gallate is viewed as the most significant active component. Not surprisingly, the leaf bud and the first leaves are richest in epigallocatechin gallate. The usual concentration of total polyphenols in dried green tea leaf is around 8 to 12 percent. Other compounds of interest in dried green tea leaf: caffeine (3.5 percent), an unusual amino acid known as theanine ( one-half of the total amino acid content, which is usually 4 percent), lignin (6.5 percent), organic acids (1.5 percent), protein (15 percent), and chlorophyll (0.5 percent).
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Coffee And Tea