Effect of Different Lipid Systems on Antioxidant Activity of Rosemary Constituents Carnosol and Carnosic Acid with and without α-Tocopherol

Abstract

The effect of oxidizing lipid substrate on the antioxidant activity of carnosol and carnosic acid were evaluated in bulk and emulsified systems. In bulk methyl linoleate, carnosic acid was a better antioxidant than carnosol on the basis of conjugated diene hydroperoxide formation, and both were more active than α-tocopherol. However, in linoleic acid carnosol was more active than carnosic acid. In bulk corn oil triglycerides, α-tocopherol exhibited the most antioxidant activity followed by carnosic acid and carnosol. In all emulsified systems, α-tocopherol consistently exhibited more antioxidant activity than carnosol and carnosic acid. In mixtures, carnosol decreased and carnosic acid increased the oxidative stability of α-tocopherol in corn oil. During oxidation carnosic acid and carnosol are converted to unknown compounds which exhibit antioxidant activity. The type and polarity of the lipid system used as a model substrate significantly affect the antioxidant activity of carnosol and carnosic acid. Keywords: Antioxidants; a-tocopherol; carnosol; carnosic acid; methyl linoleate; linoleic acid; corn oil; oil; emulsion; synergism