Logo - Rejuvenal
ORAC; oxygen radical absorbance capacity
Oxygen Radical Absorbance Capacity (ORAC) is a method of measuring antioxidant capacities of different foods. It was developed by the scientists at the National Institute on Aging in the National Institutes of Health (NIH) in Baltimore, Maryland, but it does not mean that this method is approved by NIH. Recently, US Department of Agriculture USDA listed a database of the ORAC value in its home page (www.usda.gov) without evaluation. A wide variety of foods have been tested using this methodology, with certain spices, berries and legumes rated very highly. Correlation between the high antioxidant capacity of fruits and vegetables, and the positive impact of diets high in fruits and vegetables, is believed to play an important role in the Free-radical theory of aging.
Method
The original idea of the ORAC assay is based on Glazer's study. The assay measures the oxidative degradation of the fluorescent molecule (either beta-phycoerythrin or fluorescein) after being mixed with free radical generators such as azo-initiator compounds. Azo-initiators are considered to produce peroxyl free radical by heating, which damages the fluorescent molecule,resulting in the loss of fluorescence. Antioxidant is able to protect the fluorescent molecule from the oxidative degeneration. The degree of protection will be quantified using a fluorometer. As a fluoresent probe, fluorescein is mostly used these days. Equipment that can automatically measure and calculate the capacity is commercially available (Biotek, Roche Diagnostics).
The fluorescent intensity decreases as the oxidative degeneration proceeds, and this intensity is recorded for typically 35 minutes after the addition of the azo-initiator (free radical generator). The degeneration (or decomposition) of fluorescein that is measured as the fluorescence delay becomes less prominent by the presence of antioxidants. Decay curves (fluorescence intensity vs. time) are recorded and the area between two decay curves (with or without antioxidant) is calculated. Subsequently, the degree of antioxidant-mediated protection is quantified using the antioxidant trolox (a vitamin E analogue) as a standard. Different concentrations of trolox are used to make a standard curve, and test samples are compared to this. Results for test samples (foods) have been published as "trolox equivalents" or TE.
One benefit of using the ORAC method to evaluate substance's antioxidant capacity is that it takes into account samples with and without lag phases of their antioxidant capacities. This is especially beneficial when measuring foods and supplements that contain complex ingredients with various slow and fast acting antioxidants, as well as ingredients with combined effects that cannot be pre-calculated.
Drawbacks of this method are: 1)free radicals which damage fluorescein molecule are not identified; 2)the nature of the damaging reaction is not characterized; and 3) there is no evidence that free radical is involved in this reaction. Moreover, the relationship between ORAC values and the health benefit has not been established.
Studies:
Studie1