The USDA Human Nutrition Research Center on Aging in Boston has developed an assay called ORAC (oxygen radical absorbance capacity), which qualifies the antioxidant capacity of foods. Fresh blueberries have a high level of ORAC, 2400 per 100 grams. (As a comparison, five servings of some fruits and vegetables in a typical American diet score around 1600)
In a US Department of Agriculture (USDA) laboratory at Tuft's University in Boston, Massachusetts, researchers have found that blueberries rank #1 in antioxidant activity when compared to 40 common fresh fruits and vegetables. Concord grape juice is next on the list with about two thirds of the antioxidant activity of blueberries followed by strawberries, kale, and spinach.