Background: 吀e gastric tract may be the first site where humans are exposed to postprandial oxidative stress and antioxidant activity by plant micronutrients. A昀er food intake, dietary iron, dioxygen and emulsified polyunsaturated lipids come into close contact and substantial lipid oxidation may take place [1,2]. 吀e primary lipid oxidation products, i.e. hydroperoxides, may not reach the intestine but rather decompose in the stomach into hydroxy fatty acids, aldehydes and epoxides [3], which once absorbed may participate in the atherogenicity of LDL. The aim of this work is the in vitro investigation of lipid oxidation possibly taking place in the gastric compartment and its inhibition by common dietary polyphenols. In particular, oligomeric procyanidins (PCs), whose content in the diet is probably largely underestimated, deserve more detailed investigations. Material and Methods: Sunflower oil-in-water emulsions stabilized by proteins (bovine serum albumin, sodium caseinate) and/or egg yolk phospholipids were designed in order to model the physical state of lipids after ingestion of a western diet. pH was set at 5 or 3 to simulate the initial and the middle phases of gastric digestion, respectively. Lipid oxidation was initiated at 37°C by metmyoglobin, the red pigment of meat and lipid-derived conjugated dienes and aldehydes were kinetically monitored. Epicatechin (the PC monomer) and two apple oligomeric fractions of PCs were probed for antioxidant capacity in comparison to the highly antioxidant flavonol quercetin. In a further step, the digestive enzyme pepsin was added to go closer to real gastric physiology. Results/Discussion: Over 3 h of in vitro digestion at pH 5, pepsin decreased slightly the strong antioxidant capacity of polyphenols in the PL model without affecting that in the BSA model. At pH 3, polyphenols no longer inhibited lipid oxidation whatever the presence or absence of pepsin. This suggests a large inability of the phenolic compounds to interact with the hematin cofactor released from metmyoglobin at pH < 4. Moreover, no protection was afforded in systems containing NaCas. Conclusion: Overall, lipid oxidation in gastric-like conditions mostly depends on the emulsifier type when the inhibitory effect of dietary polyphenols appears effective in the early stage of digestion.