Antioxidant activity and polyphenol content of green tea flavan-3-ols and oligomeric proanthocyanidins

The antioxidant activity and total phenolics content (TPC) of freshly prepared green tea extract (GTE) as affected by time, temperature and stirring were determined using the ferric reducing antioxidant power (FRAP) and Folin-Ciocalteu assays, respectively. Acetone-water fractions of GTE containing flavan-3-ols and oligomeric proanthocyanidins were evaluated at concentrations between 25 and 500 µg/ml. Increasing the extraction time from 3 min to 10 min resulted in a significant increase in both the FRAP values and TPC. Increasing the extraction time from 10 min to 30 min was without any significant effects on both FRAP and TPC values. Moreover, the FRAP values were correlated with the TPC. GTE fractions had widely different FRAP values that were well correlated with the TPC of the fraction. It was concluded that brewing conditions such as extraction temperature, period of extraction, ratio of tea leaves to extracting water, and stirring are important factors for determining the FRAP values and TPC in GTE. These factors should be taken into consideration during preparation for nutritional benefits during usual consumption of this beverage. Elevated FRAP and TPC values corresponded to those GTE fractions with a higher amount of phenolic compounds, which have stronger antioxidant activities.