All Natural. Signatures. 60% Cacao. Cocoa is a natural source of flavanol antioxidants. 480 mg per serving. Plant foods like berries, teas and even red wine contain many types of natural antioxidants. Cocoa beans, the seeds of the fruit of the cocoa tree, are one of the most concentrated known sources of flavanol antioxidants. Total antioxidant capacity: Hershey's Extra Dark Chocolate (1 serving 40 g).