Doc:Tea

Classification 分類

green tea

It is non-fermented, i.e., produced by drying an steaming the fresh leaves of Camellia sinensis var. sinensis to inactivate polyphenol oxidases.

oolong tea

It is produced by partial fermentation before drying.

black tea

It is fully fermented by oxidation.

red (pu-erh) tea

It is fully fermented by microorganisms including Aspergillus spp. and Penicillium spp.

Per capita mean consumption of tea in the world is 120 mL/day , the second most consumed beverage in the world (next to water).

Tea Composition

The major phenolics in green tea include catechins (flavan 3-ols). They are (-)-epigallocatechin-3-gallate (EGCG; 59% of total catechins), (-)-epigallocatechin (EGC; 19%), (-)-epicatechin-3-gallate (ECG; 13.6%), and (-)-epicatechin (EC; 6.4%) . Catechins are converted to theaflavins and thearubigins in black tea . A cup of tea may contain 90 mg of EGCG , but in human, EGCG is less bioavailable (i.e. absorbed) than other green tea catechins. After drinking tea, the plasma level of catechins reach their peaks (between 1-10 µmol/L) in 2 - 4 h . After 24 h, plasma levels of EGCG and EGC return to baseline, but that of ECG remains elevated in methylated forms.

Major Composition (%) Compound Green tea Black tea Infusion (3min) Proteins 15 15 trace Amino acids 4 4 3.5 Fiber 26 26 0 Others, carbohydrates 7 7 4 Lipids 7 7 trace Pigments 2 2 trace Minerals 5 5 4.5 Phenolic compounds 30 5 4.5 Oxidized phenolics 0 25 4.5