Inhibitory effect of the hot water extracts prepared from various kinds of teas on the platelet aggregation induced by collagen or ADP was investigated by use of turbidimetry. A standard method used was the extraction with 40ml of boiling water for 3min on each 1g tea sample. Examination on various teas with the different manufacturing process indicated that the aggregation inhibitory effect was observed generally on any kind of tea extracts tested, though the activity differed from a strong one (e.g. Japanese green tea, the inhibition ratio is over 50%) to a weak one (e.g. Aoyagi tea, about 10%). Among the black teas, Kenya and Sri Lanka Uva teas showed strong activity, while Darjeeling tea was weak. Japanese green teas were generally effective and the activity was on the order of Sencha> Maccha>Gyokuro.Chinese semi-fermented teas gave only a weak activity. High-performance liquid chromatographic analysis on the main black and green tea extracts showed that the effective ones were rich in the content of catechins in the Japanese green teas and of theaflavin and catechins in the black teas. Among the purified samples of six catechins and three theaflavins and caffeine, (-)-epicatechin, (+)-catechin, (+)-gallocatechin, and theaflavin mono-gallate showed a marked inhibitory activity.
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