Ascorbic acid is a water soluble vitamin and has diverse functions in the body including as essential role in the hydroxylation reactions for the synthesis of collagen.
It is widely regarded as an essential antioxidant in the human body has even been called ‘the most important antioxidant in human plasma’.
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.
Antioxidant can be defined as any substance that when present at low concentration compared to those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate.
In-vitro experiments have shown that ascorbic acid can act as a chain breaking antioxidant in lipid peroxidation. Studies of the antioxidant activity of human blood plasma suggest that ascorbic acid is the major extracellular antioxidant.
As an oxygen scavenger, ascorbic acid also 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 can also undergo autoxidative destruction especially in the presence of transition metals such as copper and iron, which in turn promotes and accelerates the autoxidation of other macromolecules such as unsaturated lipids.
Ascorbic acid is widely used as an oxygen scavenger and synergist in numerous food applications and has a higher oxidation potential (greater reducing capacity) than most phenolic antioxidants.
Ascorbic acid as antioxidant
