Antioxidant properties of tea extracts as affected by processing

The changes in the antioxidant properties of green and black tea extracts as a consequence of processing and storage conditions were evaluated through measurements of chain-breaking activity, oxygen scavenging capacity and redox potential. Pasteurisation and storage as well as forced oxygenation in both tea extracts caused an increase in the optical density and a decrease in the reducing power of the beverages; both were accompanied by unexpected increases in the chain-breaking activity of the beverages. Simple model systems containing catechin at a concentration similar to that found in the tea extracts were also considered to simulate the effects of enzymatic browning in tea. Possible explanations for the chain-breaking activity gain observed in the tea extracts as a consequence of processing were proposed.