Bioavailable standardised extract from Green Tea leaves
Tea is second only to water as the most popular beverage in the world; it is prepared by infusion of the leaves of Camellia sinensis L., originally grown in the South of China where it has been cultivated since the ancient times. According to the Chinese tradition, tea drinking was introduced in China in the third millenium BC, during the reign of the legendary emperor Shen Nong. At first tea was regarded as a medicine, and its stimulant and invigorating properties were much appreciated by the Buddist monks, who contributed to its diffusion throughout China and Japan by encouraging the habit of tea drinking as aremedy for intemperance.
The development of a flourishing trade led to the introduction of tea cultivations in Japan, and since the 19th century in India, Ceylon, Java, Sumathra, Georgia and Kenya.
Types of tea
There are three main groups of teas: black tea, oolong tea and green tea.
- Black tea is obtained from fermented (oxidized) leaves. During fermentation, extensive enzymatic oxidation of catechin derivatives takes place.
- Oolong (or Wulong) tea is obtained from partially fermented leaves; heating at a predetermined stage blocks the fermentation process when required.
- Green tea is produced by steaming or drying fresh leaves at elevated temperatures, inactivating oxidative enzymes and thus preserving catechins.
Green tea is widely used in China, Japan and other Eastern countries, while black tea is more diffuse in the Western countries. Nevertheless, green tea is growingly consumed also in North America and Europe. The average consumption of tea catechins in the Eastern countries rises to 700-900 mg of tea catechins (by HPLC), whereas one “Western” cup of tea* only provides 50 mg of tea catechins (by HPLC), a much lower quantity compared to the Asian average consumption. These data are highly hypothetic, since catechin degrade rapidly in commercial teas, and the extent of extraction critically depends on the temperature and length of infusion.
Green tea infusions contain flavanols (catechin polyphenols), flavonols and phenolic acids(1).
Several flavanols have been isolated and identified from green tea, and two of these, (-)-epigallocatechin 3-O-gallate (EGCG) and (-)-epigallocatechin (EGC) exhibited a marked antioxidant activity.
*2 g dry leaves in 200 mL hot water, infused for 5 minutesExpand Bibliography
- Gutman R. L., Ryu B. H., Herbalgram 37, Special Supplement, 34 (1996)