THE EFFECT OF FATTY-ACID UNSATURATION ON THE ANTIOXIDANT ACTIVITY OF BETA-CAROTENE AND ALPHA-TOCOPHEROL IN HEXANE SOLUTIONS

The effect of fatty acid unsaturation on the antioxidant ability of be ta-carotene and alpha-tocopherol to inhibit azobis-isobutyronitrile (A IBN)-induced malondialdehyde (MDA) formation is investigated in a hexa ne solution. A positive correlation is shown between the fatty acid un saturation and MDA production in homogeneous solutions. Both beta-caro tene and alpha-tocopherol act as chain-breaking antioxidants in our mo del, effectively suppressing AIBN-induced MDA formation. When alpha-to copherol is added to fatty acid solutions, a lag phase of about 30 min is observed and a propagation phase is produced at a rate dependent o n the degree of unsaturation and similar to that observed in the absen ce of the antioxidant. A specific inhibition of initiation phase by al pha-tocopherol is confirmed by its total consumption after 30 min of i ncubation with AIBN. On the other hand, when beta-carotene is added, a lag period is not observed and the inhibition of propagation phase pr ogressively increases in relation to the degree of fatty acid unsatura tion. These data present different antioxidant roles for beta-carotene and alpha-tocopherol in AIBN-induced lipid peroxidation and suggest t hat beta-carotene can be a very effective antioxidant in highly unsatu rated membranes, such as those enriched with n-3 polyunsaturated fatty acids (PUFA).