ORAC tests may not predict antioxidant activity

Ingredients that have a high ORAC (oxygen radical absorbance capacity) value or are good at scavenging harmful free radicals in the laboratory are not necessarily good antioxidants, researchers have claimed.

University of Massachusetts researchers argue tests such as ORAC, which assess how effective compounds are at scavenging harmful free radicals, may have limited value in predicting their antioxidant activity in foods.
The researchers measured the free radical scavenging activity of compounds including ascorbic, ferulic and rosmarinic acid. They then added them to minced beef and corn oil in water to see how effective they were at inhibiting fat oxidation. This can cause nasty flavours, textures and colours, and general deterioration.
While ORAC and other tests revealed ferulic acid and rosmarinic acid to be the most effective free radical scavengers, ferulic acid did not inhibit lipid oxidation at all in minced beef. And rosmarinic acid was only moderately successful.
By contrast, propyl gallate and TBHQ (tertiary butylhydroquinone), which performed badly in the scavenging tests, were the most effective antioxidants in the beef.
By mopping up free harmful radicals (natural byproducts of respiration), antioxidants are believed to tackle ageing and diseases associated with oxidative stress such as arthritis and cancer, and prevent food spoilage.
However, similar challenges highlighted in the study above have also been raised by nutrition scientists. They question the marketing of foods based on ORAC values because what matters is how antioxidants behave in our bodies, not in a test tube.
Modern cellular antioxidant activity (CAA) tests developed in the US helped address this problem. But further testing was still needed to confirm how dietary antioxidants behaved in the body, accepted Dr Rui Hai Liu, of Cornell University.
Liu, who has been using the CAA tests to look at the bioactivity of antioxidants from 25 different fruits inside human liver cancer cells, said: “We found that wild blueberries had the highest antioxidant activity, with other berries and pomegranates also showing strong performance.
“While further testing is needed to confirm how dietary antioxidants are absorbed by and go to work in the human body to prevent cancer and other chronic diseases, we’re encouraged by the response in this initial screening measure.”
Meanwhile, new research into the bioactive compounds in some fruits suggested that their beneficial effects had little to do with their antioxidant properties, said Coressence, which makes apple-based functional ingredients.
Chief executive Richard Wood said: “Our story is not about antioxidants. The flavanols like (-)-epicatechin that we are interested in may act as antioxidants in a test tube using ORAC tests. However, it is now known that their vascular benefits are the result of other mechanisms, and their effectiveness has little to do with their antioxidant properties.”
Dr Paul Kroon - an academic based at the UK’s Institute for Food Research who has been researching apple bioactives and cardiovascular health, said: “We’re interested in compounds that are actually found in the blood, rather than flavonoids in food before it is eaten, as only these compounds will actually come into contact with human tissues and have an effect on arterial health.”