If you spend a lot of time reading about nutrition (which I do), it starts to feel as if we're all in some sort of contest to see who can eat the most antioxidants. Those who are interested in (dare I say, obsessed with?) antioxidant nutrition will often talk about a food's ORAC value. As in, "Wild blueberries have an ORAC value of 9,621, while regular blueberries only have an ORAC of 4,669!" What on earth are these people talking about?
ORAC stands for Oxygen Radical Absorbance Capacity. It's a lab test that attempts to quantify the "total antioxidant capacity" (TAC) of a food by placing a sample of the food in a test tube, along with certain molecules that generate free radical activity and certain other molecules that are vulnerable to oxidation . After a while, they measure how well the sample protected the vulnerable molecules from oxidation by the free radicals. The less free radical damage there is, the higher the antioxidant capacity of the test substance. There are actually a handful of different tests designed to measure total antioxidant capacity in this way, but the ORAC is probably the best known and most popular.
The nice thing about this method is that it measures the antioxidant activity of a food rather than the levels of specific nutrients, such as vitamin C or E. After all, there are thousands of unique antioxidant compounds in plants, most of which we haven’t even discovered yet. There’s no way we could measure them all individually. This approach would also capture any synergistic effects between the various nutrients—ways in which nutrients are more effective in combination than they are individually.