There are many types of free radicals and free radicals' initiators. Some of the most active are the reactive oxygen species (ROS). These are molecules or ions formed thanks to the partial reduction of oxygen, and include singlet oxygen, superoxides, peroxides and hydroxyl radical.

Although Reactive Oxygen Species are not the only source of pro-oxidant activity in the living organisms, they are good indicators of the potential dangers of oxidative stress.

One of the most common methods to rate the antioxidant power of foods and nutritional supplements, is to evaluate their efficacy against Reactive Oxygen Species. The test called ORAC, is an analytic method to measure this efficacy in biological samples in vitro.

ORAC is the acronym for Oxygen Radical Absorbance capacity. It is measured by comparing the antioxidant activity of a sample against that of a standard substance, called Trolox.

According to the USDA, diets rich in fruits and vegetables are considered to be an excellent source of antioxidants. And this antioxidant capacity is believed to play a role in the fight against oxidative stress and its consequences.

Maquiberry, the marvelous little fruit from the Chilean Patagonia is rated with the highest ORAC value among the known fruits.

This may explain some of its properties and its success in being one of the sacred medicinal plants of the Mapuche people.