Antioxidants
Vitamin C, vitamin E, and beta-carotene are well known antioxidants with recommended daily values. However, there are many compounds found in food known as phytochemicals that have no set recommendation, yet they produce antioxidant activity. Foods contain different phytochemicals collectively referred to as flavonoids. These include isoflavones, carotenoids, and many more. They are too numerous to attempt to list.
While no clear, widely accepted and well-established definition for antioxidants has been developed within the scientific community, the FDA states "the term antioxidant may be used for a substance for which there is scientific evidence that, following absorption from the gastrointestinal tract, the substance participates in physiological, biochemical, or cellular processes that inactivate free radicals or that prevent free radical-initiated chemical reactions." Furthermore, the "FDA recognizes that foods may contain a mixture of substances, both nutrients and non-nutrients, that participate in antioxidant processes. However, there are no reliable methods available that measure the antioxidant activity of all substances that participate in antioxidant reactions when an entire food is consumed."