The effect of fatty acid unsaturation on the antioxidant activity of β-carotene and α-tocopherol in hexane solutions

The effect of fatty acid unsaturation on the antioxidant ability of β-carotene and α-tocopherol to inhibit azobisisobutyronitrile (AIBN)-induced malondialdehyde (MDA) formation is investigated in a hexane solution. A positive correlation is shown between the fatty acid unsaturation and MDA production in homogeneous solutions. Both β-carotene and α-tocopherol act as chain-breaking antioxidants in our model, effectively suppressing AIBN-induced MDA formation. When α-tocopherol 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 on the degree of unsaturation and similar to that observed in the absence of the antioxidant. A specific inhibition of initiation phase by α-tocopherol is confirmed by its total consumption after 30 min of incubation with AIBN. On the other hand, when β-carotene is added, a lag period is not observed and the inhibition of propagation phase progressively increases in relation to the degree of fatty acid unsaturation. These data present different antioxidant roles for β-carotene and α-tocopherol in AIBN-induced lipid peroxidation and suggest that β-carotene can be a very effective antioxidant in highly unsaturated membranes, such as those enriched with n-3 polyunsaturated fatty acids (PUFA).