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SummaryThe influence of black tea polyphenols on plasma lipid levels was investigated in rats fed a 15% lard and 1% cholesterol diet. Our laboratory has demonstrated that green tea catechins have a variety of biological activities, including antibacterial (1-3), antioxidative (4, 5), antitumor (6) and hypocholesterolemic (7) activities. There have been many reports that green tea and oolong tea decrease plasma lipids in rodents and humans (8)(9)(10)(11)(12)(13)(14). However, few investigators have reported on the effect of black tea on plasma lipids (15-18), and there have been even fewer reports on the reduction of plasma lipids. In this study, we investigated the effects of black tea polyphenols on plasma lipids. Materials and methodsPreparation of black tea polyphenols, instant black tea and epigallocatechin gallate. Black tea polyphenols (BTP) were prepared according to the following method: 2kg of instant black tea (IBT) dissolved in 20L of hot water was extracted with ethyl acetate (9L) in order to obtain the polyphenolic fraction. The solid recovered from the solvent was dissolved in 200mL of water and 300mL of acetone, and the resulting solution was washed twice with 1,500mL of chloroform 30times 337

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Inhibitory effects of individual tea catechins ((‐)‐epicatechin, (‐)‐epigallocatechm, (‐)‐epicatechin gallate, (‐)‐epigallocatechin gallate), black tea extract and oolong tea extract on hepatocarcinogenesis were investigated. Male F344 rats received a single dose of diethylnitrosamine (200 mg/kg, i.p.), and thereafter phenobarbital (0.05%) was administered in the drinking water for a period of 6 weeks. Tea catechins, black tea extract or oolong tea extract were given during the entire experimental period, during only the initiation period or during only the promotion period. All four tea catechins, black tea extract and oolong tea extract (0.05 or 0.1%) significantly decreased the number and area of preneoplastic glutathione S‐transferase placental form‐positive foci in the liver. These results suggest that tea catechins, black tea extract and oolong tea extract have a chemopreventive action against hepatocarcinogenesis.