Simulated intestinal digestion of green and black teas

Previous studies have shown that significant changes to green tea catechins occur as a result of changes in pH similar to those found in the gastrointestinal tract. In this study we have demonstrated that the sum of the antioxidant activities attributable to the four major catechins in brewed green and black tea samples was less than the total measured antioxidant activity, although there was a high degree of correlation between antioxidant activity and total measured polyphenol concentration. In addition, incubation of either form of tea at acid pH (as found in the stomach) had little effect of the concentration of individual catechins. However, incubation at slightly alkaline pH, similar to that found in the small intestine, resulted in a rapid decline in the concentrations of both green and black tea catechins, but with a lesser reduction in antioxidant activity and polyphenol concentration.