Antioxidant and Pro-Oxidant Effects of Polyphenolic Compounds and Structure-Activity Relationship Evidence

The research and characterization of new bioactive substances, for the new design of functional foods, nutraceuticals, or drugs, has been intensified. Several studies showing controversial results of exogenous antioxidants, debating that the type, dosage and matrix of these antioxidants may be determining factors impacting the balance between beneficial and deleterious effects of these natural compounds (Bouayed & Bohn, 2010). There are also some proofs that they act as pro-oxidants, under certain conditions, such as high doses or the presence of metal ions (Decker, 1997; Raza & John, 2005; Watjen et al., 2005). The antioxidant or pro-oxidant activity intimately depends on their concentration (Bouayed & Bohn, 2010). The consequences of pro-oxidant activity could be the possible damage to the biomolecules such as DNA, proteins and lipids, and the consequent cellular death (Aruoma, 2003).