Tuesday, July 15, 2008

Ascorbic acid function as antioxidant

Ascorbic acid function as antioxidant
L-ascorbic acid, its salts (sodium-L-ascorbic and calcium-L-ascorbate), and its isomers (D- and L-isoascorbic acid) are classified as generally recognized as safe substances by FDA. The L stereoisomer of ascorbic acid is the only from which carries significant vitamin activity. The vitamin activity of D-ascorbic is only one-tenth that of the L-form. The activity of D- and L-isoascorbic acid is only one twentieth that of L-ascorbic acid. FDA requires that label declaration if D-isoascorbic acid be made using the common name erythorbic acid to prevent potential misleading of consumers.

Ascorbic acid’s function in food systems is complex and depends on a number of factors. Its antioxidants activity is affected by the oxidation-reduction potential of the food system, time, PH, oxygen, trace metals, enzymes, other oxidants, and the concentration of the vitamin in comparison to the concentration of other reactants in the oxidation process. Other than bisulfites, ascorbic acids, its salt and its fatty acid ester (ascorbyl palmitate) are the only antioxidants permitted in foods which are capable of scavenging oxygen out of solution. Ascorbic acid is therefore, commonly used in canned or bottled products, particularly in beverages with headspace of air.

As an oxygen scavenger, ascorbic acid serves as a reducing agent. It transfers its hydrogen atoms to oxygen, making the oxygen unavailable for further reaction. In the process, the ascorbic acid is oxidized to dehydroascorbic acid, which in turn can function as an oxidizing agent by removing hydrogen from reducing agents such as sulfhydryl groups. Ascorbic acid and dehydroascorbic acid are thus reversible forms of vitamin C and both have physiological activity. Further, ascorbic acid may exert a chelating action, binding heavy chemical, if present will promote oxidation. When chelated with heavy metals, ascorbic acid loses its physiological vitamin activity.
Ascorbic acid function as antioxidant

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