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THE USE OF EXTRACTED PHENOLIC COMPOUNDS FROM GREEN AND BLACK TEA AS NATURAL ANTIOXIDANTS

This study was carried out to separate and identify green and black tea phenolic compounds. These compounds were added to sunflower oil as natural antioxidants at levels 150, 200 and 250 ppm and stored in amber glass bottles at 40  C for nine weeks. The antioxidative effectiveness of these compounds was compared with pure catechin, butylated hydroxyanisole (BHA) and butylatedhydroxy toluene (BHT). The chemical properties of green and popular black tea collected from Egyptian local markets were also studied. Green tea leaves contained higher percent of moisture, ether extract and protein than those of black tea leaves. In green tea 37.15% of the dry matter is soluble in hot water, while 37.65 - 44.50% of the dry matter is soluble in hot water depending on the origin of black tea leaves. Caffeine constitutes 2.45 - 2.78% of the dry matter of tea leaves. higher percent of tannin was found in green tea leaves (19.65%), while black tea leaves contained lower levels (13.29 - 14.22%). The data showed that, green tea contained higher amounts of polyphenolic compounds (32.75%) than those of black tea (2.7.20 - 31.12%). High performance liquid chromatography (HPLC) analysis indicated that both types of tea extracts contained nine phenolic compounds. Caffeic acid was the main phenolic acid in green tea extracts (36.97%), followed by p-hydroxybenzoic acid (18.18%), catechin (14.62%), ferullic acid (8.77%), gallic acid (8.20%) and chlorogenic acid (5.24%). While black tea contained higher amounts of tannic acid (35.26%) followed by caffeic acid (30.20%), catechin (10.33%) gallic acid (5.78%) and p-hybroxybenzoic acid (4.55%). Green tea extracts at 150 ppm possessed appreciable antioxidants activity greater than black tea extracts, pure catechin and BHA. Increasing the level added from 150 to 200 and 250 ppm lead to decreasing peroxide values (pv) and thiobarbituric acid (TBA) formed and retarding oxidative rancidity in sunflower oils. Green and black tea represent an excellent source of nature antioxidant. The antioxidative capacity of green tea is much higher than that of black tea. So, it could be recommended to use green tea rather than black tea because of the high contents of natural antioxidants as well as it low content of tannins.