Polyunsaturated fatty antioxidant action

Figure 45-6. Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) of the cell and the aqueous phase (cytosol). (R-,free radical PUFA-00-, peroxyl free radical of polyunsaturated fatty acid in membrane phospholipid PUFA-OOH, hydroperoxy polyunsaturated fatty acid in membrane phospholipid released as hydroperoxy free fatty acid into cytosol by the action of phospholipase Aj PUFA-OH, hydroxy polyunsaturated fatty acid TocOH, vitamin E (a-tocopherol) TocO, free radical of a-tocopherol Se, selenium GSH, reduced glutathione GS-SG, oxidized glutathione, which is returned to the reduced state after reaction with NADPH catalyzed by glutathione reductase PUFA-H, polyunsaturated fatty acid.)...

Sea animals are rich in soluble dietary fibers, proteins, minerals, vitamins, antioxidants, phytochemicals, and polyunsaturated fatty acids, with low caloric value. Polysaccharides from marine animals have been reported to possess biological activities with potential medicinal values in addition to their current status as a source of dietary fibers and prebiotics. Moreover, they have a lot of dietary fiber, which lowers blood cholesterol, and iodine, which improves metabolism, vascular and cardiac action, body temperature, and perspiration regulation, and are effective in... 

For some time, the effects of and responses to vitamin E have been interpreted in terms of an antioxidant mechanism of action. However, several observations have raised the question as to whether other mechanisms could be involved. For example, the effects of selenium and vitamin E on growth and polyunsaturated fatty acid synthesis in cultured mouse fibroblasts could not be reproduced by artificial antioxidants [198, 199]. The specific requirement of (+ )-a-toco-pherol for the phenotypic differentiation of the rotifer [200] may not be through an antioxidant mechanism. The effects of vitamin E on differentiation of neuroblastoma cells [201] and metamorphosis of various species [202] are likely to be due to a growth-factor-like action. A study on the interaction... 

Vitamin E (a-tocopherol), a potent antioxidant, appears to offer protection against injuries caused by 02, 03, and N02, and nitrosamine formation. Male rats supplemented with daily doses of 100 mg tocopheryl acetate and exposed to 1.0 ppm 03 have been shown to survive longer than vitamin E-deficient rats. The action of 03 is attributed in part at least to free radical formation. In addition, there is sufficient evidence that vitamin E protects phospholipids of microsomal and mitochondrial membranes from perox-idative damage by reacting with free radicals. Because lipid peroxidation is associated with decrease in oxidase activities, it is expected that the enzyme activity is affected by dietary vitamin E. Maximum activity has been observed when diets included both polyunsaturated fatty acids and vitamin E. 

As previously mentioned, tocopherols/tocotrienols may be added to foods for the stabilization of their polyunsaturated fatty acids. Chemical conditions and the physical state of the food to be stabilized have a major influence on lipid oxidation and antioxidant reactions. The number of possible reaction routes and stabilizing and destabilizing factors is enormous (e.g., Pokorny, 1987 Warner, 1997 Frankel, 1998). In foods, tocopherols can be regenerated from their tocopheroxyl radicals by reducing compounds such as ascorbic acid. Regeneration is possible only if the lipid-soluble tocopheroxyl radical and the water-soluble ascorbic acid are close enough to be able to react with each other, e.g., in emulsion. Thus, the interfacial region between lipid and water phases is important for the antioxidant action of tocopherols and tocotrienols (Frankel, 1998). 

Several mechanisms of antioxidant action have been proposed. The presence of antioxidants may result in the decreased formation of the reactive oxygen and nitrogen species in the first place. Antioxidants may also scavenge the reactive species or their precursors. Vitamin E is an example of this latter behavior in its inhibition of lipid oxidation by reaction with radical intermediates generated from polyunsaturated fatty acids. Some antioxidants can bind the metal ions needed to catalyze the formation of the reactive oxidants. Other antioxidants can repair oxidative damage to biomolecules or can influence enzymes that catalyze repair mechanisms. 

Antixmdants The direct action of oxygen in the air is the chief cause of the destruction of the fats in food. Carbon-carbon double bonds in polyunsaturated fatty acids are particularly susceptible. Oxidation produces a complex mixture of volatile aldehydes, ketones, and acids that causes a rancid odor and taste. Foods kept wrapped, cold, and dry are relatively protected from air oxidation. The most common antioxidant food additives are butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), which act by releasing a hydrogen atom from their — OH groups as a free radical (H ). 

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