From Wikipedia:

Oxygen Radical Absorbance Capacity (ORAC) is a method of measuring antioxidant capacities of different foods. It was developed by the scientists at the National Institute on Aging in the National Institutes of Health (NIH) in Baltimore, Maryland, but it does not mean that this method is approved by NIH. Recently, US Department of Agriculture (USDA) listed a database of the ORAC value in its home page (www.usda.gov) without evaluation.  A wide variety of foods have been tested using this methodology, with certain spices, berries and legumes rated very highly.  Correlation between the high antioxidant capacity of fruits and vegetables, and the positive impact of diets high in fruits and vegetables, is believed to play an important role in the Free-radical theory of aging. 

The ORAC value of foods is exceptionally important. Notice in this chart that Artichokes have very high in minerals and nutrients.

The average person needs roughly 1,500 ORAC capacity values a day.  An artichoke heart is more than 7,000 capacity values!

USDA data on foods with high levels of antioxidant phytochemical

Food

Serving Size

Antioxidant Capacity Per Serving Size 

 Cinnamon (Ground) 100 grams

267,536 

 Aronia Black Chokeberry (Aronia Melanocarpa)100 Grams 

16,062 

 Small Red Bean 1/2 Cup Dried Beans

13,727 

 Wild Blueberry1 Cup 

13,427 

 Red Kidney Bean1/2 Cup Dried Beans 

13,259 

Pinto Bean 1/2 Cup 

11,864 

Blueberry 1 Cup (Cultivated Berries) 

9,019 

 Cranberry1 Cup (Whole Berries) 

 8,983

LOOK!
Artichoke Hearts 
1 Cup, Cooked 

 7,904

Blackberry 1 Cup (Cultivated Berries) 

7,701 

 Prune1/2 Cup 

7,291 

 Raspberry1 Cup 

6,058 

 Strawberry1 Cup 

 5,938

Red Delicious Apple 1 Apple 

5,900 

 Granny Smith Apple1 Apple 

5,381 

 Pecan 1 Oz

5,095 

Sweet Cherry 1 Cup 

4,873 

 Black Plum1 Plum 

 4,844

 Russet Potato1 Cooked Potato 

4,649 

Black Bean 1/2 Cup Dried Beans 

 4,181