ABSTRACT
Free radical damage may lead to cancer. Green tea contains antioxidant phenolic compounds that interact and stabilize free radicals. Green tea is widely consumed around the world. Conventionally, tea has been prepared by brewing dried tea leaves with hot water. Due to their worldwide acceptance, ready-to-drink green-tea beverages with different concentrations of tea have been manufactured for consumer convenience. This study aimed to compare amount of phenolic compounds and antioxidant activity between green tea beverages and tea freshly prepared from dried green-tea leaf. Green-tea beverages without artificial flavoring (n=16) and dried green-tea leaf (n=5), available in Bangkok, were collected. Phenolic compounds and antioxidant activity were determined by Folin-Ciocalteu and Ferric Reducing Antioxidant Power methods. The differences in the amounts of phenolic compounds and antioxidant activity, between green tea beverages and tea freshly prepared from dried green-tea leaf, were analyzed by Mann-Whitney U Test using a 95% confidence limit. The correlation between the amount of phenolic compounds and antioxidant activity of green-tea beverages, and tea freshly prepared from dried green tea leaf, were determined by Spearman Rank Correlation Coefficient. It was found that the amount of phenolic compounds and antioxidant activity of tea freshly prepared from dried green tea leaf were significantly higher than the green tea beverages (p\<0.05). A positive correlation between the amount of phenolic compounds and antioxidant activity were found in both green tea beverages (r=0.845) and tea freshly prepared from dried green-tea leaf (r=0.975). (Thai Cancer J 2010;30:127-134)