Synthetic antioxidants, function

Antioxidants (qv) have a positive effect on oils when present in the proper concentration. Sterols and tocopherols, which are natural antioxidants, may be analy2ed by gas-Hquid chromatography (glc), high performance Hquid chromatography (hplc), or thin-layer chromatography (tic). Synthetic antioxidants maybe added by processors to improve the performance or shelf life of products. These compounds include butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), / fZ-butyUiydroquinone (TBHQ), and propyl gallate. These materials may likewise be analy2ed by glc, hplc, or tic. Citric acid (qv), which functions as a metal chelator, may also be deterrnined by glc. 

When two antioxidants are used together, a synergistic improvement in activity usually results. Synergism can arise from three combinations (1) homosynergism — two chemically similar antioxidants (for instance, two hindered phenols) (2) autosynergism — two different antioxidants functions that are present in the same molecule (3) heterosynergism — the cooperative effect between mechanistically different classes of antioxidants, such as the combined effect of primary and secondary antioxidants. Thus, combinations of phenols and phosphites are widely used to stabilize synthetic rubbers. 

No unequivocal unique function for vitamin E has been defined. However, it does act as a hpid-soluble antioxidant in cell membranes, where many of its functions can be provided by synthetic antioxidants. Vitamin E is the generic descriptor for two famihes of compounds, the tocopherols and the tocotrienols (Figure 45—5). The different vitamers (compounds having similar vitamin activity) have different biologic potencies the most active is D-a-tocopherol, and it is usual to express vitamin E intake in milhgrams of D-a-tocoph-erol equivalents. Synthetic DL-a-tocopherol does not have the same biologic potency as the namrally occurring compound. 

It has been known for some time that vitamin E can act as an antioxidant within the body [21, 61] and that the biological potency of the tocopherols is proportional to their antioxidant activity [62], Synthetic antioxidants, which often have structures unrelated to that of the vitamin, are also capable of preventing the symptoms of vitamin E deficiency [23, 24, 63, 64]. The general proposal [63, 65], therefore, is that the function of vitamin E is one of an in vivo antioxidant, protecting membrane phospholipids from attack by free radicals generated within the cell. 

For a long time, it was considered that, unlike the other vitamins, vitamin E had no specific functions rather it was the major Upid-soluble, radicaltrapping antioxidant in membranes. Many of its functions can be met by synthetic antioxidants however, some of the effects of vitamin E deficiency in experimental animals, including testicular atrophy and necrotizing myopathy, do not respond to synthetic antioxidants. The antioxidant roles of vitamin E and the trace element selenium are closely related and, to a great extent, either can compensate for a deficiency of the other. The sulfur amino acids (methionine and cysteine) also have a vitamin E-sparing effect. 

The best-established function of vitamin E is as a lipid-soluble antioxidant in plasma lipoproteins and cell membranes. Many of the antioxidant actions are unspecific, and a number of synthetic antioxidants have a vitamin E-sparing effect. There is considerable overlap between the antioxidant roles of vitamin E and selenium (Section 4.3.2). 

Vitamin E functions as a lipid antioxidant hoth in vitro and in vivo a numher of synthetic antioxidants will prevent or cure most of the signs of vitamin E deficiency in experimental animals. Polyunsaturated fatty acids undergo oxidative attack by hydroxyl radicals and superoxide to yield alkylperoxyl (alkyl-dioxyl) radicals, whichperpetuate a chain reactionin the lipid-withpotentially disastrous consequences for cells. Similar oxidative radical damage can occur to proteins (especially in a lipid environment) and nucleic acids. 

Vitamin E-deficient female animals suffer death and resorption of the fetuses. This was the basis of the original biological assay of the vitamin female rats were maintained for 2 to 3 months on a vitamin E-free diet and then mated. Impregnation and implantation proceed normally but, if they are not provided with vitamin E, the fetuses die and are resorbed. Five days after mating, the animals were killed, and the number of surviving fetuses gave an index of the biological activity of the test compound, relative to standard doses of a-tocopherol. Synthetic antioxidants can replace vitamin E for this function, but selenium cannot. 

Natural phenolic antioxidative activity is an additional benefit in the use of these smoke flavourings. The higher boiling point phenolics, in particular, possess antioxidative functionality similar to that of commercially used synthetic phenolic antioxidants. 

Bhabak KP, Mugesh G (2010) Functional mimics of glutathione peroxidase bioinspired synthetic antioxidants. Acc Chem Res 43 1408-1419... 

Although vitamin E was identified as a dietary essential for animals in the 1920s, it was not until 1983 that it was clearly demonstrated to be a dietary essential for human beings. Unlike other vitamins, no unequivocal physiological function for vitamin E has been defined it acts as a lipid-soluble antioxidant in cell membranes, but many of its functions can be replaced by synthetic antioxidants. As discussed in section 7.4.3.3, there is epidemiological evidence that high intakes of vitamin E are associated with a lower incidence of cardiovascular disease. 

Polyphenols are commonly present in fruits, vegetables, nuts, seeds, and flowers. Moreover, polyphenols can be found in such products as cocoa, tea, coffee, wine, jam, and chocolate. Polyphenolic compounds are also often applied in cosmetics, medicines, pharmaceuticals, dietary supplements, and in recent years, for the production of functional foods. The food industry offers a variety of new functional products in which the polyphenol content is usually higher than in products of natural origin. Milk enriched with soy isoflavones, chocolate enriched in procyanidins, drinks with higher amounts of anthocyanins, functional drinks enriched with extracts of tea—these are just a few products that are the result of functional foods revolution. On the other hand, the use of synthetic antioxidants in the food industry is of great concern among consumers who seek to limit their intake. Toxicological and nutritional research indicates adverse effect of some synthetic antioxidants used in food. The use of additives in food products, mainly in edible fats, means that more attention should be paid to antioxidants that are derived from natural plant extracts and used as food additives. 

There are numerous synthetic and natural compounds called antioxidants which regulate or block oxidative reactions by quenching free radicals or by preventing free-radical formation. Vitamins A, C, and E and the mineral selenium are common antioxidants occurring naturally in foods (104,105). A broad range of flavonoid or phenoHc compounds have been found to be functional antioxidants in numerous test systems (106—108). The antioxidant properties of tea flavonoids have been characterized using models of chemical and biological oxidation reactions. 

The importance of cell death mediated by oxidative damage has led to the popularity of antioxidants as potential therapeutics. A variety of naturally occurring (vitamin C, vitamin E) and synthetic (lazaroids) antioxidants have been smdied as possible remedies for a wide variety of ailments. Large doses of vitamin E have been studied as a putative therapy in Alzheimer s disease, functioning through the inhibition of amyloid-induced oxidative destruction of neuronal membranes within the brain. 

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