Simulation of Phenolic Compounds Transformations and Interactions in an In Vitro Model of the Human Alimentary Tract

Phenolic compounds play an important role in the defense system of the human organism against reactive oxygen species. They are present mainly in fruit and vegetables, but their bioavailability is the key factor determining their concentration in blood and tissues. The aim of this article was to study the transformations that apple polyphenols undergo during digestion. An in vitro model with dialysate membranes simulating the human alimentary tract was used for evaluating the composition and antioxidant properties of fresh apples and products of their digestion in dialysates. Epicatechin, chlorogenic acid, and procyanidins were the main antioxidant compounds in the whole fruits and flesh of the two varieties of apples analyzed. In the apple peel additionally quercetin glycosides were present. As a result of in vitro digestion both polyphenolic compounds concentration and the antioxidant activity of the dialysates increased as compared to the raw materials (from 35% to 95% and from 50% to 236%, respectively). In the simulated alimentary tract, it was proved that procyanidins disintegrate to (+)catechin, which is well absorbed from the small intestine, while chlorogenic acid and quercetin glycosides were characterized by a low bioavailability.