Sunday, June 28, 2020

Chemical constituents of green tea

Green tea is produced without fermentation and undergoes minimal oxidation possible during processing. Green tea can be the raw material for extracts which are used in different beverages, dietary supplements and also in cosmetic items.

Most of the beneficial effects of green tea are attributed to its polyphenolic flavonoids, known as catechins the major flavonoid. These polyphenols account for up to 40% of the dry weight of green tea.

The chemical composition of green tea varies with genetic strain, climatic conditions, soil properties, plucking season, position of the leaf, processing and storage.

Chemical composition is complex consisting of proteins (15–20% dry weight) whose enzymes constitute an important fraction; amino acids (1–4% dry weight) such as teanine or 5-N-ethylglutamine, glutamic acid, tryptophan, glycine, serine, aspartic acid, tyrosine, valine, leucine, threonine, arginine, lysine; carbohydrates (5–7% dry weight) such as cellulose, pectins, glucose, fructose, sucrose; lipids as linoleic and a-linolenic acids; sterols as stigmasterol; vitamins (B, C, E); xanthine bases such as caffeine and theophylline; pigments as chlorophyll and carotenoids; volatile compounds such as aldehydes, alcohols, esters, lactones, hydrocarbons, etc.; minerals and trace elements (5% dry weight) such as Ca, Mg, Cr, Mn, Fe, Cu, Zn, Mo, Se, Na, P, Co, Sr, Ni, K, F, and Al.

Caffeine is mainly a trimethyl derivative of purine 2, 6-diol and is produced from leaves of the tea plant from the ancient time. Coffee beans contain about 1.5 % caffeine, while caffeine content of green tea is up to 5%. It functions as a cardiac and also as a diuretic. It can also stimulate the cerebral cortex which results in central nervous system excitation.

Carbohydrate is the major constituent of tea leaf that includes cellulosic fibre and the next is protein, but these components are not soluble.

Generally, the major catechins of tea leaves are (+)-catechin (C), (−)-epicatechin (EC), (+)-gallocatechin (GC), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin gallate (EGCG), and (+)-gallocatechin gallate (GCG).

The antioxidant properties of catechins are mainly related to the number and position of hydroxyl group in the molecules and consequently binding and neutralization of free radicals by these hydroxyl groups. Previous studied have shown that tea catechins are excellent electron donors and effective scavengers of physiologically relevant reactive oxygen species in vitro, including superoxide anions.

Among total nitrogen found in the green tea infusion, one fifth of them originate from caffeine and related compounds. Other forms of nitrogenous compounds found in tea infusion are amino acids, amides, certain proteins, and nucleic acids.
Chemical constituents of green tea

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