Basic Principles of the ORAC Assay
The ORAC assay measures the time-dependent decrease in the fluorescence intensity of the β-PE indicator protein, resulting from oxygen radical damage. On a molar basis, the β-PE protein reacts with oxygen radicals over 100 times slower than most biological antioxidants such as thiols, uric acid, bilirubin and ascorbate. However, β-PE is over 60 times more reactive than other non-antioxidant proteins. 2 Therefore, all active antioxidants are completely oxidized before the β-PE protein starts to becomes oxidized, thus facilitating the measurement of the total antioxidant capacity of the sample being tested.
Quantitation of Antioxidant Activity
Each point on the reflects
the level of antioxidant protection at that time, which is contributed
by many different antioxidants. Genox has developed a computer macro
which measures the amount of fast acting antioxidants, usually aqueous
soluble, that protects the (β-PE protein 100% by completely inhibiting
free radical propagation. The fast acting ORAC value constitutes only
a small fraction of the total ORAC value. Over
60% of the total ORAC is from the high concentration of slow acting antioxidants
like the lipid soluble antioxidants (carotenoids, tocopherols), flavonoids,
polyphenols and other phytochemicals. This separation technique increases
the sensitivity of the assay in showing differences among different groups
of individuals.
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