Anti- and prooxidant properties of carotenoids

Carotenoids can be effective singlet oxygen quenchers and inhibit free-radi cal induced lipid peroxidation. A remarkable property of beta-carotene (la) is the change from an antioxidant to a prooxidant depending on oxygen pres sure and concentration. In the present study a considerable number of carot enoids (1a, 2c, 2d, 2e, 3a, 4a, 5a, 6a, 7a, 8a, 8h, 8i, 8j, 9f, 10a, 11a, 1 2g) was investigated using two independent approaches: 1. Comparison of the ir effects on inhibition of the free-radical oxidation of methyl linoleate, and 2. The direct study of the effect of oxygen partial pressure upon thei r rates of oxidation. It is shown that some carotenoids (7a, 8a) are even m ore effective than the well-known compounds beta-carotene (la) and astaxant hin (5a) and are powerful antioxidants without any prooxidative property. D ifferent carotenoids display different behaviour depending on chain length and end groups. The influence of these functional groups on the antioxidati ve reactivity is discussed.