An in vitro gastrointestinal model, which simulates the conditions of the human digestive tract, was used in this work to determine the potential antioxidant activity in Jaś Karłowy bean flour, extruded Jaś Karłowy bean products (chips) and black chokeberry juice. The aim of the study was to investigate changes in the level of phenolic compounds and antioxidant activity under in vitro conditions which closely resemble those occurring in the human digestive tract. We examined the effect of human fecal flora on the antioxidant activity of products undergoing digestion, which are a rich source of antioxidant compounds. Results obtained in the research indicate that the in vitro gastrointestinal tract model applied in this work can be successfully used to study changes in the level of phenolic compounds. Our observations show that digestion of Jaś Karłowy bean flour, an extruded product from bean and black chokeberry juice in the gastrointestinal tract model has an influence on the antioxidant activity and the level of phenolic compounds in these products of Jaś Karłowy bean flour, extruded product from bean and black chokeberry juice. The highest antioxidant activity, approx. 30 mg Trolox/g during the digestion process, was noted for both flour and extruded bean products. All products examined were found to stimulate the growth of intestinal microorganisms, however black chokeberry juice decreased only the growth of bacteria from the Enterococcus species.