Resveratrol (3,4’,5-trihydroxystilbene) is a stilbenoid, a derivative of stilbene, and is produced in plants to ward of fungal infection. It exists as two geometrical isomers: cis-(Z) and trans-(E). Trans-resveratrol is the active form. Trans-resveratrol can undergo isomerization to the cis- form when heated or exposed to UV irradiation.
Resveratrol is found in varying amounts in grapes (primarily the skins), raspberries, mulberries, blueberries, bilberries, cranberries, peanuts, scots pine, eastern white pine, and the roots and stalks of giant knotweed and Japanese knotweed (Polygonum cuspidatum).