Effect of carnosic acid, quercetin and alpha-tocopherol on lipid and protein oxidation in an in vitro simulated gastric digestion model

Carnosic acid, quercetin and alpha-tocopherol are well-known antioxidants in many biological systems. However, their antioxidative effect during food digestion against lipid and protein oxidation is not well known. Therefore, in this study, an in vitro simulated gastric digestion model was used to investigate their stability during gastrointestinal conditions and their antioxidative properties during low pH digestion. In general, the stability of the antioxidants in the different steps of digestion was in the order of alpha-tocopherol > quercetin > carnosic acid. Salivary components, as well as the acidity of the gastric juice, were responsible for the reduction in antioxidants. Both alpha-tocopherol and quercetin were able to lower lipid oxidation during digestion, while the effect on protein oxidation was not clear. In contrast, carnosic acid did not have any effect on lipid oxidation and tended to stimulate protein oxidation. This study clearly demonstrated that the environmental conditions are of major importance to the properties of antioxidant compounds.