Fig. 2.

Chemical structures of dietary antioxidant compounds. Polyphenol family members that exhibit indirect antioxidant activity include resveratrol, a stilbenoid found in red wine; quercetin, a flavonol found in red and yellow onions; curcumin, a curcuminoid found in turmeric and mustard; and luteolin, a flavone found in celery, parsley, and thyme. Glucosinolate breakdown products that have indirect antioxidant properties include the isothiocyanates sulforaphane and phenethyl isothiocyanate and the epithionitriles 1-cyano-2,3-epithiopropane and 1-cyano-3,4-epithiobutane: glucosinolates that give rise to these compounds are found in cruciferous vegetables, such as broccoli.