Antioxidants are added to oils and fats to prevent rancidity and normally this is best achieved when mixtures of antioxidants are used for this purpose. Natural antioxidants include some vitamins (particularly vitamin E and ubiquinols) and some phenolic compounds occurring in foods, especially spices. Most regulatory bodies permit the use of various gallates such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in dairy products and fats. Some directives also regard calcium disodium EDTA as an antioxidant for use in salad dressings and mayonnaise. BHA and BHT are used mainly for the protection of unsaturated fats and oils as well as baked goods, cereals, nuts (particularly walnuts), milk powder and in dehydrated potato products such as potato chips and snacks.
The safety of these synthetic antioxidants has been questioned lately,38 and in the case of BHA sufficient evidence for carcinogenicity in experimental animals has been found to prompt changes (but not withdrawals) in the recommended usage of this compound.37,39 BHA has been shown to produce hyperplasia and/or tumours in the forestomach of rats, mice and hamsters.37 BHT, on the other hand, has been shown to have adverse effects on thyroid function, and haematological studies have also revealed that some, but not all, species show haemorrhaging effects and/or reduction in prothrombin index.38 Some evidence also exists for a carcinogenic effect of BHT, as demonstrated by two recent Danish and Japanese studies.37
The natural antioxidants, such as the tocopherols (vitamin E) and ubiquinols have a cyclic nucleus and a hydrocarbon tail, and the antioxidant properties are produced by the cyclic nucleus of these molecules. When these compounds form part of the membrane systems of cells, the orientation in cell membranes is, however, accomplished by the other components of the molecules. Synthetic antioxidants contain only the fragments which ensure the antioxidant properties of the compounds, and this may be the source of their destructive and perturbative action on cell membranes and can explain their toxicity.40 Natural antioxidants can be very
effective, and research has shown that they can compete with the synthetic varieties.41