Antioxidant capacity is an overall ability of organisms or food to catch free radicals and prevent their harmful effect. Antioxidative effect includes protection of cells and cellular structures against harmful effect of free radicals, especially oxygen and nitrogen. Antioxidants are substances with antioxidative properties. They are most commonly present in fruits and vegetables. In addittion, other foods such as wine, meat or eggs contain these substances.
Antioxidative systems include antioxidative enzymes, that is, superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, and nonenzymatic substrates, such as glutathione, uric acid, lipoic acid, bilirubin, coenzyme Q, vitamin C (L-ascorbic acid), vitamin A (retinol), vitamin E (tocopherol), flavonoids, carotenoids, teine compounds in green tea, and others. Some biomolecules are also biologically active and clinically significant antioxidants, for example, transferrin, ferritin, lactoferrin, ceruloplasmin, hemopexin, haptoglobin, and uric acid.
Bioquochem recommends FRAP assay kit for total antioxidant activity of single antioxidants in aqueous solution and added to plasma.
Ferric Reducing Antioxidant Power – FRAP Assay Kit
The assay described here measures the ferric reducing ability of plasma (FRAP). At low pH, when a ferric complex is reduced to the ferrous form (Fe2+), an intense blue color with an absorption maximum at 593 nm develops.
This reaction is nonspecific and any half-reaction which has a less-positive redox potential, under reaction conditions, than the Fe3+/Fe2+ complex half reaction will drive Fe3+ complex reduction. Acidic conditions favor reduction of the complex and, thereby, color development, showed that an antioxidant is present.
Fe3+-C+AOH → Fe2+-C(blue)(λmáx= 593 nm)
Scheme 1: Reaction of Fe3+ complex with antioxidants (AOH)