What is an ORAC Score?
Wednesday February 17, 2010Oxygen Radical Absorbance Capacity (ORAC) is a method of measuring antioxidant capacities in biological samples. 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 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 the peroxyl 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. Fluorescein is currently used most as a fluorescent probe. 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 typically recorded for 35 minutes after the addition of the azo-initiator (free radical generator). The degeneration (or decomposition) of fluorescein is measured as the presence of the antioxidant slows the fluorescence decay. Decay curves (fluorescence intensity vs. time) are recorded and the area between the 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. (more…)




