The ability of high molecular weight melanoidins extracted from coffee, barley coffee, and dark beer to inhibit lipid peroxidation during simulated gastric digestion of turkey meat has been investigated. Results showed that melanoidins decrease the synthesis of lipid hydroperoxides and secondary lipoxidation products. Coffee melanoidins at 3 mg/mL reversed the reaction and broke down hydroperoxides to concentrations lower than the initial value. Barley coffee and dark beer melanoidins were less effective, and even at 12 mg/mL did not reverse the reaction. The proposed mechanism of action involved Fe(2+) chelating capacity, heme-binding ability, and radical-scavenging activity. Melanoidins were characterized for their content in total proteins, carbohydrates, and phenolics, and the relationship between the chemical composition and the antioxidant activity of dietary melanoidins was investigated. Coffee melanoidins, which contain more phenolics and proteins with respect to the other melanoidins, showed greater antioxidant activity with respect to the other melanoidins tested.