Antioxidant mechanism of carnosic acid: Structural identification of two oxidation products

To determine the antioxidant mechanism of food phenolics against the oxidat ion of food components, the reaction of carnosic acid, an antioxidative con stituent of the popular herbs sage and rosemary, was investigated in the pr esence of ethyl linoleate and the radical oxidation initiator 2,2'-azobis-( 2,4-dimethylvaleronitrile). During this process, carnosic acid was oxidized to an o-quinone and a hydroxy p-quinone, the chemical structures of which were confirmed by physical and chemical techniques, From a quantitative tim e course analysis of the production of these quinones, an antioxidant mecha nism of carnosic acid is proposed, consisting of the oxidative coupling rea ction with the peroxyl radical at the 12- or 14-position of carnosic acid a nd subsequent degradation reactions.