Have you ever heard of a measure called ORAC? ORAC stands for Oxygen Radical Absorbance Capacity. It is a measure of the antioxidant activity of foods. Basically, researchers pit a bunch of free radicals (bad) against a sample of food and see how well the antioxidants in the food can “disarm” them.
However, I think it is worth mentioning that raw, unprocessed cocoa beans are among the highest scoring foods that have been tested.
Dark chocolate is loaded with organic compounds that are biologically active and function as antioxidants. These include polyphenols, flavanols, catechins, among others.
One study showed that cocoa and dark chocolate contained more antioxidant activity, polyphenols and flavanols than other fruits they tested, which included blueberries and Acai berries.