Antioxidant activity of beta-carotene-related carotenoids in solution.

The effect of the antioxidant activity of beta-carotene and related carotenoids on the free radical-oxidation of methyl linoleate in solution was examined by measuring the production of methyl linoleate hydroperoxides. Canthaxanthin and astaxanthin which possess oxo groups at the 4 and 4'-positions in the beta-ionone ring retarded the hydroperoxide formation more efficiently than beta-carotene and zeaxanthin which possess no oxo groups. The rates of autocatalytic oxidation of canthaxanthin and astaxanthin were also slower than those of beta-carotene and zeaxanthin. These results suggest that canthaxanthin and astaxanthin are more effective antioxidants than beta-carotene by stabilizing the trapped radicals.