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Tea Polyphenols in Promotion of Human Health

Tea Polyphenols in Promotion of Human Health
Feb. 20,2023

Tea is the most widely used beverage worldwide. Japanese and Chinese people have been drinking tea for centuries and in Asia, it is the most consumed beverage besides water. It is a rich source of pharmacologically active molecules which have been implicated to provide diverse health benefits. The three major forms of tea are green, black and oolong tea based on the degree of fermentation. The composition of tea differs with the species, season, leaves, climate, and horticultural practices. Polyphenols are the major active compounds present in teas. The catechins are the major polyphenolic compounds in green tea, which include epigallocatechin-3-gallate (EGCG), epigallocatechin, epicatechin-3-gallate and epicatechin, gallocatechins and gallocatechin gallate. EGCG is the predominant and most studied catechin in green tea. There are numerous evidences from cell culture and animal studies that tea polyphenols have beneficial effects against several pathological diseases including cancer, diabetes and cardiovascular diseases. The polyphenolic compounds present in black tea include theaflavins and thearubigins. In this review article, we will summarize recent studies documenting the role of tea polyphenols in the prevention of cancer, diabetes, cardiovascular and neurological diseases.

The beverage tea is made from the infusion of the leaves of Camellia sinensis. The world’s tea consumption is highest for black tea, followed by green tea, oolong tea, and white tea. Black tea is made by crushing and drying fresh tea leaves to effect fermentation prior to final processing and is consumed usually in the United States, Europe, Africa, and India. During fermentation, some of the catechins combine to form complex theaflavins and other flavonoids, which offer characteristic taste and color to black tea. To prevent fermentation, green tea is prepared when the fresh leaves are processed swiftly and the oolong tea is partially fermented.

Tea possesses antioxidant properties with traces of proteins, carbohydrates, amino acids, lipids, vitamins and minerals. It also contains an extensive range of chemical compounds, but mainly polyphenols account for the aroma and beneficial health effects of tea. The polyphenols in green tea are credited with its beneficial properties against several diseases in many reported studies . These polyphenols are present in much higher concentrations in green tea than black or oolong tea and this accounts for their antioxidant properties. The distinctive polyphenolic compounds present in green tea are called as catechins, like (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin-3-gallate (ECG) and (-)-epicatechin (EC). EGCG account for 50–70% of catechins. EGCG is the major catechin in tea and accounts for most of the research carried out with green tea. One cup of green tea contains up to 200 mg of EGCG, which has been shown to have chemopreventive/chemotherapeutic effects against several types of cancers. Proper drinking of green tea is three to five cups per day, which accounts for a minimum of 250 mg of catechins per day . Several in-vitro and in-vivo studies have reported the antioxidant effects of GTP. We have earlier discussed the anticarcinogenic effects of green tea, its effects on various receptor tyrosine kinases, signal transduction pathways and metastasis . 

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