Antioxidative activity of green tea catechins in canola oil

Jasmine tea is one of the most popular beverages consumed in China. In the present study, green tea catechins (GTCs) were extracted from jasmine tea and their antioxidative activity was examined in canola oil heated at 95 degrees C for various time. The yield of crude GTC extracts was 7.4% of dry tea leaves and it mainly consisted of 51.2% (-) epigallocatechin gallate (EGCG), 18.7% (-) epigallocatechin (EGG), 12.3% (-) epicatechin (EC) and 11.8% (-) epicatechin gallate (EGG). Both the oxygen consumption test and the fatty acid analysis showed that the GTC extracts exhibited strong antioxidative effect. At 200 ppm, four major epicatechin derivatives tested demonstrated varying antioxidative activity in the decreasing rank of EGC > EGCG > EC > EGG. They were even more protective than BHT against lipid oxidation in canola oil under the same conditions. Furthermore, thermal loss of the GTCs was significantly less compared to that of BHT in canola oil heated at 95 degrees C. Faster thermal loss of BHT was attributed to volatilization and steam distillation due to the high temperature. We conclude that the GTCs asa mixture of EGG, EGCG, EC and ECG may replace BHT as antioxidants in processed foods.