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Quantitative and qualitative changes in the phenolic composition of red wine may occur during digestion in the lumen, particularly when other dietary components are present. In this study, mixtures of red wine, iron, and ascorbic acid, meat or casein were subjected to a simulated gastrointestinal digestion. This process involves incubation of samples for 4.5 h at 37°C, at different pH values, in the presence of peptic enzymes and fractionation of digests through a dialysis membrane with a molecular weight cut-off of 6000–8000. Selected phenolic compounds were determined in undigested samples and in their dialysable digests by reversed-phase high-performance liquid chromatography. A dramatic decrease in the concentration of the selected phenolic compounds was observed in all samples after they were digested in vitro. Moreover, when iron and/or protein were added to red wine samples, changes in the phenolic profile of the undigested and of the in vitro digested samples were detected. These results suggest that interactions between red wine phenolic compounds and iron, protein and/or digestion components are important determinants of the physicochemical properties and the concentration of these phenolic compounds in the lumen. The in vitro methodology employed herein offers a tool for the study of phenolic compounds under conditions of simulated gastrointestinal digestion, incorporating lumenal events that may affect phenolic compounds.