Phenolics and antioxidant activity of bamboo leaves soup as affected by in vitro digestion

Bamboo leaves soups were subjected to in vitro digestion (including separated oral, gastric and small intestinal digestions, and complete digestion containing above three stages), and their phenolics and antioxidant activities were determined. Compared to control groups, total phenolic content (TPC) in treated groups (including undigested and digested groups) increased at gastric digestion stage but decreased at other digestion stages, and the decrease in small intestinal digestion stage (19.97%) was nearly the same with that in complete digestion stage (19.39%). The antioxidant activity in digested groups almost changed accordingly to their TPC but with no significant difference (p > 0.05) as compared with undigested groups; similar results were found in four main individual phenolics including cryptochlorogenic acid, chlorogenic acid, neochlorogenic acid and isoorientin, and their contents were negatively correlated to the pH value of digestion buffers (-0.68 < r < -0.80, p < 0.01). These results indicated that the change of phenolic content and antioxidant activity in digested bamboo leaves soups mainly resulted from the pH of digestion buffers rather than digestive enzymes. In addition, the decrease of phenolics may mainly occur at small intestinal digestion stage where the pH value is the highest in the digestive system.