The free radical reactions were evaluated in an aqueous model system which mimics the physicochemical conditions of the digestive tract (37°C and pH 3.5, 5, 6.5). Oxidants (Fe2+/H2O2) and antioxidants were added in concentrations which can be found in a bolus after ingestion of a balanced meal composed of meat and vegetables. Detection of the free radicals was achieved using two specific probes (Nitroblue Tetrazolium for superoxide radicals, O2°-, and Terephthalate for hydroxyl radicals, OH°). The level of the detected radicals increased with increasing oxidant concentrations. The pH effect varied according to the free radical. Detected O2°- decreased with increasing pH while a biphasic effect of pH was observed with OH°, with a maximum of detected OH° at pH 5. Antioxidants had various impacts on the free radicals. Plant-derived antioxidants; -carotene and polyphenols (caffeic acid, rutin, chlorogenic acid and quercetin) had antagonist effects on the two radicals. They increased the level of detected O2°- and decreased OH° detection. Trolox C (a water soluble analogue of vitamin E) did not significantly impact the free radical detection. From these data a predictive mathematic model of oxidations in the digestive tract will be built.