Update on the Biological Characteristics of the Antioxidant Micronutrients: Vitamin C, Vitamin E, and the Carotenoids
Section snippets
The Antioxidant Hypothesis
Interest in the antioxidants stems from the growing understanding that a substantial number of free radicals are generated as an ordinary process of oxygen metabolism and that a wide range of conditions are associated with either an excess generation of free radicals or an inadequate antioxidant defense system (5). Exogenous sources, such as radiation, air pollution, and smoking, can also generate free radicals. Free radicals are reactive chemical species that contain one or more unpaired
Chemistry and Analysis
Vitamin C is the generic descriptor for all compounds exhibiting qualitatively the biological activity of ascorbic acid, which includes the oxidized form, dehydroascorbic acid (DHAA). Isoascorbic (erythorbic) acid, which is used widely as a food preservative, possesses antioxidant properties similar to L-ascorbic acid but lacks antiscorbutic activity (29). The newer high-performance liquid chromatography (HPLC) methods for quantifying vitamin C in biological specimens, foods, and
Chemistry and Analysis
Vitamin E is the generic term used to describe a group of at least eight compounds that exhibit the biological activity of a-tocopherol. The group comprises α-, β-, γ-, and δ-tocopherol and α-, β-, γ-, and δ-tocotrienol. All of these compounds occur as a variety of isomers; for example, eight stereoisomers of α-tocopherol result from the synthesis of this compound. The natural isomeric form is RRR-α-tocopheiol (also known as d-α-tocopherol), and the synthetic form is described as all racemic or
Chemistry and Analysis
Carotenoids are pigments that are found in plants and microorganisms but are not synthesized in animals. Nearly 600 of these compounds have been identified (see Fig. 2) (2), (78), and less than 10% of these compounds can be metabolized to retinol and function as vitamin A precursors in mammals. Human plasma contains only a fraction of the total carotenoids that have been identified in the food supply (79), The predominant plasma carotenoids are lutein, β-cryptoxanthin, lyco-pene, oc-carotene,
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