Availability of polyphenols in fruit beverages subjected to in vitro gastrointestinal digestion and their effects on proliferation, cell-cycle and apoptosis in human colon cancer Caco-2 cells

Three fruit beverages: Fb (grape–orange–apricot), FbFe (Fb + iron sulphate) and FbFeM (FbFe + skimmed milk) were subjected to in vitro gastrointestinal digestion. Addition of Fe and milk decreased the phenolic content of Fb by 13% and 55%, respectively. The digestion process decreased the phenolic content by 47%, 60%, and 70% in Fb, FbFe and FbFeM with respect to the initial, non-digested, Fb. Caco-2 cells were incubated for 4 h daily for four days or continuously for 24 h with bioaccessible fractions obtained after the digestion (digests). Polyphenols were not metabolised by Caco-2 cells. Fb digest (∼50 μM total phenolics) was the sample that led to the highest inhibition of cell proliferation under the two experimental conditions. Fb digest did not induce apoptosis but ceased cell-cycle in the S-phase which is associated to a decrease in B1 and D1 cyclin levels upon incubation for 24 h.