ORAC is the standard test, adopted by the US Department of Agriculture, to measure the potency of antioxidants in food. The test was developed by Dr. Guohua Cao, a physician and chemist who worked at the National Institute on Aging in Baltimore, Maryland. The ORAC test, though not the be all and end all of antioxidant testing, gives a good idea of the free-radical-destroying potential of a given food. It does this by measuring the time an antioxidant takes to react as well as the capacity of antioxidants within the sample food. It combines these elements into one measurement that is commonly expressed in terms of a 100 gram sample.
It has been suggested that humans should consume about 5000 ORAC units a day for maximum benefits. Unfortunately, most people do not eat nearly enough vegetables and fruit, or the right type of vegetables and fruit, to achieve this. For example, to get your daily ORAC dose from apples, you would need to eat 2,294 grams of apple (or about 22 apples). However, as you can see from the below chart, eating just 20 grams of goji berries will cover you.
It is important to remember, however, that there is a lot more to measuring a food's antioxidant capcity than ORAC. Since different antioxidants have different effects, it is still important to eat a variety of foods (including apples) with high antioxidant levels. For example, although strawberries have a higher ORAC score than spinach, spinach has been shown to be more effective than strawberries in boosting blood antioxidant scores. So, although eating a large amount of antioxidants is always a plus, it is important to eat a variety of healthy foods, not only for their antioxidant levels, but for their other nutritional properties as well.