Oxygen radical absorbance capacity

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Oxygen Radical Absorbance Capacity (ORAC) is a method of measuring antioxidant capacities of different foods. It was developed at the National Institute on Aging in Baltimore, Maryland. High scoring foods include Mangosteen, Acai, Cerasus (Montmorency tart cherries) prunes, raisins, blueberries, kale, spinach, spices and cocoa. Foods with moderately high ORAC values include wild blueberries, pomegranates and black raspberries.

The assay measures the oxidative degradation of fluorescein after being mixed with peroxyl radical. The reaction alone is compared to the reaction in the presence of a standard antioxidant (trolox, a vitamin E analogue) and the antioxidant sample being tested. The fluorescent intensity of the fluorescein decreases as it gets oxidized, and measurements of this intensity are taken every minute for 35 minutes after the initial addition of the oxidant. The oxidative decay of fluorescein is inhibited in the presence of antioxidants. A graph of the kinetic curve (fluorescein intensity vs. time) is generated and the area under the curve is calculated. Different concentrations of trolox are measured to make a standard curve, and test samples are compared to this. Final results for test samples are published as "trolox equivalents" or TE (Huang et al., 2005).

One benefit of using the ORAC method to test a 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.

In 2004, scientists with the US Department of Agriculture (References, Wu et al.) published an updated list of ORAC values for over 100 common foods that are commonly consumed by the U.S. population (fruits, vegetables, nuts, seeds, spices, grains, etc.). Values were reported as micromoles of Trolox equivalents (TE, vitamin E derivative) per gram both for lipid-soluble ("lipophilic" as for carotenoids) and water-soluble ("hydrophilic" as for phenolics) antioxidant chemicals in foods, thus were a sum of lipophilic and hydrophilic values or total ORAC.

The values are considered to be more accurate than previously published ORAC numbers because lipophilic values were being included for the first time. The data of Wu et al. showed that all plants have variable amounts of both lipophilic and hydrophilic phytochemicals with antioxidant properties contributing to total ORAC.

When comparing ORAC data, care must be taken to ensure that the units and food being compared are similar. Some evaluations will compare ORAC units per grams dry weight, others will evaluate ORAC units wet weight and still others will look at ORAC units/serving. Under each evaluation, different foods can appear to have higher ORAC values. Although a raisin has no more antioxidant potential than the grape from which it was dried, raisins will appear to have a much higher ORAC value per gram wet weight than grapes due to their reduced water content. Likewise, watermelons large water content can make it appear as though they are very low in antioxidants. To say then that chocolate has "more antioxidant" potential than blueberries is tenuous at best. While ounce per ounce chocolate may have a higher ORAC value, on the comparision of dry weight, we see blueberries have a higher ORAC value. Additionally, considering the ORAC value per calorie could be of some utility, as understanding just how much antioxidizing potential one could incorporate from a product into one's diet would determine the real utility of the product.

The range of ORAC for common fruits was around 1.40 micromol TE per gram (watermelon) to 95 (cranberry). Lowbush blueberry (wild blueberry) was also very high at 92.6. For vegetables or legumes, it was 1.15 (cucumber) to 149 small red (red kidney bean); for nuts, 7.19 (cashew) to 179.4 (pecan); and for dried fruits, 23.87 (medjool dates) to 85.78 (prune). By comparison, different species of apples had ORAC values of 22.10 to 42.75 micromol TE per gram, white potato was under 11, peanut was 31.66 and tomato about 4.00 Spices (clove, cinnamon) showed the highest ORAC values (>2500, converted to micromol TE per gram). Cocoa has a high ORAC value, giving baking chocolate a value of 1032 and milk chocolate an average of 71.30.

A recent paper by Schauss et al. published in the peer-reviewed Journal of Agricultural and Food Chemistry reported an extremely high total ORAC value of 1027 micromol TE per gram for a freeze-dried fruit pulp and skin powder from the Acai berry (Euterpe oleracea) (Schauss et al. 2006). This is the highest ORAC value ever reported for a fruit or vegetable to this date, after converting values of fresh food weights to dry weights. This includes a hydrophilic ORAC antioxidant capacity of 997 micromol TE per gram, and a lipophilic ORAC antioxidant capacity of 30 micromol TE per gram.

Recently, a number of health food companies have capitalized on the ORAC rating, with dozens selling concentrated supplements that they claim to be "the number one ORAC product". Most of these values have never been published in the scientific literature so are difficult to evaluate. It is not known whether such values are accurate or how absorbable and functional these concentrated antioxidants are in the human body.

[edit] References

• Commercial ORAC assays and antioxidant information, Brunswick Laboratories Inc., [1]
• Huang D, Ou B, Prior RL. The chemistry behind antioxidant capacity assays. J Agric Food Chem. 2005 Mar 23;53(6):1841-56 PMID 15769103
• Schauss A, Xianli W, Prior R, Ou B, Huang D, Owens J, Agarwal A, Jensen G, Hart A, Shanbrom E. Antioxidant Capacity and Other Bioactivities of the Freeze-Dried Amazonian Palm Berry, Euterpe oleraceae Mart. (Acai). J Agric Food Chem 2006 Nov 1;54(22):8604-10. PMID: 17061840
• Wu X, Beecher GR, Holden JM, Haytowitz DB, Gebhardt SE, Prior RL. Lipophilic and hydrophilic antioxidant capacities of common foods in the United States. J Agric Food Chem 2004 Jun 16;52(12):4026-37 PMID 15186133

[edit] See also

• Polyphenol antioxidants
• Reduction potential

[edit] External links

• ORAC levels of various foods These are "old" data from the ORAC assay used before 2004 and should be viewed only as qualitative rankings. A revised ORAC assay used since 2004 provides quantitative values several times higher than these measurements. See an abstract of the reference report at this link from PubMed [2].
• Discussion of total antioxidant assays and results