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Y. J. LIU and B. S. PAN. Food Science Department, National Taiwan Ocean University, Keelung, Taiwan, Keelung, 202, Taiwan

Green tea extract has potent antioxidative and preventive activities in coronary heart disease. The metabolites of arachidonic acid catalyzed by lipoxygenase (LOX) are bioactive compounds involved in immune regulation and defense against pathogens. LOX activities of diseased animals are higher than those found in normal animals. A synergistic interaction may occur between 15-LOX catalyzed peroxide derivatives and heme protein-catalyzed oxidation, which decreases the potency of the endogenous antioxidants and enhances the oxidation of low-density lipoproteins (LDL) that increase atherogenicity.

The purpose of the present study was to determine whether green tea extracts are inhibitory to both the LOX-catalyzed and the heme proteins-catalyzed oxidation of lipids, resulting in reduced risk of atherogenicity.

Green tea was extracted with hot water for 5 to 90 min. LOX's extracted from gills of live grey mullet and tilapia as test models. The antioxidative activity was determined by the inhibition capacity on the heme proteins-catalyzed peroxidation of linoleic acid measured with rapid photometric assay. The inhibition effects on LOX activity were assayed on arachidonic acid and measured using oxygen electrode and reverse phase HPLC. Blood thinning effects were observed in vitro by mixing green tea extract with fish red blood cells. The changes in rheological properties were compared at constant hematocrit with and without green tea extract.

Green tea extract showed inhibitory effects on both hemoglobin-catalyzed and LOX-catalyzed oxidation of linoleic acid and arachidonic acid. Similar inhibitory effects were found on LOX extracts from tilapia gill and grey mullet gill. Both in vivo and in vitro studies showed green tea extract caused the blood flow behavior to become closer to Newtonian-type with a thinning consistency.

These results suggest that green tea contains strong antioxidants that can inhibit hemoglobin-catalyzed oxidation of linoleic acid and LOX activity. Uptake of green tea may have preventive effect in atherosclerosis.