As consumers get comfortable with the term 'antioxidant,' manufacturers and suppliers are turning to ORAC assays to score the antioxidant capacity of their supplements, foods and beverages. The higher the score, the better, goes the thinking.
But the question remains whether an ORAC score means anything more than marketing hype. Among the issues: there is no industry standard for measuring the oxygen radical absorbance capacity (ORAC); growing conditions can yield different ORAC values; cooking or freezing foods can affect an ORAC score; and absorption — the ultimate goal — can effectively nullify an ORAC score.
"Having the largest number doesn't necessarily mean the best," according to Ron Prior, PhD, who helped develop the procedure at the USDA Human Nutrition Research Center in 1995. "It depends on the foods and what phytochemicals are in there and what happens during the absorption and metabolism process. We're finding some of these compounds are metabolized extensively or not absorbed effectively and so not much gets into the blood or absorbed into the tissue."
Even if an antioxidant is effectively metabolized, each has its own strengths in terms of which free radicals it most effectively scavenges. So, in striving to meet the USDA's recommended level of 3,000 to 5,000 ORAC units daily, people probably need to consume a variety of types of antioxidants.
In other cases, the critical factor appears to be which antioxidant is present in a food and which free radical it's fighting. "Some of those that are highest — particularly berries — the compounds primarily responsible for their antioxidant activity are anthocyanins," said Prior. "Those are rather unstable and not that much gets absorbed."
ORAC values can also vary within the same type of product. A March study published in Phytotherapy Research found that wheat grass grown under four different conditions yielded four different ORAC values.
"The genetic background can affect it, but also growing season and conditions of growth affect it as well," said Prior. "A lot of compounds in the flavonoids tend to be produced in response to a stress on the plant, whether that's an insect infestation or drought. Time of harvest also impacts it."