The antioxidant and nutritional effects of tocopherols, ascorbic acid and beta-carotene in relation to processing of edible oils.

Tocopherols belong to a class of phenolic antioxidants which can inhibit lipid autoxidation by scavenging free radicals and by reacting with singlet oxygen. In vegetable oils alpha-tocopherol inhibits the effects of singlet oxygen during sensitized photoxidation. Ascorbic acid has a complex multi-function, acting as a hydrogen donor, as a metal inactivator, and as a peroxide destroyer. beta-Carotene protects lipids by interfering with photosensitized oxidation, and behaves as a reducing agent by trapping radicals. After processing of vegetable oils, about 60-70% of the tocopherols remain in the oil. However, the tocopherol content in processed vegetable oils, is generally above the optimum range for antioxidant activity. On the other hand, beta-carotene is almost completely removed during processing of vegetable oils. For antioxidant purposes, both beta-carotene and ascorbic acid must be added to vegetable oils after deodorization. The vitamin E activity of alpha-tocopherol may be attributed to its very efficient inhibition of in vivo lipid oxidation. In addition to its singlet oxygen quenching properties, beta-carotene has good radical-trapping properties at low partial pressures of oxygen, which prevail in healthy tissues. In biological systems, alpha-tocopherol and beta-carotene exhibit synergism by reinforcing their mutual activities. Synergism also takes place in a cascade where ascorbic acid can be regenerated at the expense of more oxidizable substrates. Our results suggest that singlet oxygen and free radical species may significantly contribute to the fluorescence formed from the interaction of DNA with linolenate hydroperoxides in the presence of iron and ascorbic acid. A better understanding of the biological effects of lipid oxidation products is needed to conserve the nutritional value of foods containing unsaturated lipids.