ANTIOXIDATIVE EFFECT OF ETHANOL TEA EXTRACTS ON OXIDATION OF CANOLA OIL

There is an increasing interest in the biological effects of natural a ntioxidants present in teas on formation of in vivo free radicals, car cinogenesis, and atherogenesis. Teas are traditionally classified into six major groups, namely, green, yellow, white, black, dark-green, an d oolong teas. The present study examined the antioxidative activity o f ethanol extracts from these six major groups of teas against oxidati on of heated canola oil. The oxidation was conducted at 100 degrees C by monitoring oxygen consumption and changes in linoleic and linolenic acids in canola oil. The ethanol extracts of green, yellow, and white teas strongly inhibited oxidation of canola oil compared to butylated hydroxytoluene, probably due to the presence of natural polyphenols. In contrast, oolong teas examined exhibited only moderate antioxidativ e activity because of the partial destruction of natural polyphenols b y semifermentation. The ethanol extracts of black, dark-green, and gin seng teas studied showed little or no protection to canola oil from li pid oxidation, probably due to the complete destruction of natural pol yphenols by fermentation during manufacturing processes.