Plant phenolic compounds antioxidant capacity

DNA damage in the presence of cytochrome P450s (CYPs) and Cu(II) in vitro or in cells [Yoshino et al., 2004 Ahsan et al., 1999]. At higher concentrations curcumin exhibited genotoxicity and cytotoxicity in different systems [Cao et al., 2007]. At last, in vivo intervention trials using typical antioxidants such as ascorbate or carotenes yielded mostly disappointing results in terms of protection against oxidation-related diseases, sometime even increased the incidences of diseases [Stevenson and Hurst, 2007 Dinkova-Kostova and Talalay, 2008]. Obviously, the direct antioxidant capacity of plant phenolic compounds cannot explain their cytoprotective activities. 

Phenols or phenol groups are a common structure of several secondary plant metabolites. Characterized by at least one hydroxyl function attached to a benzene ring, such molecules can be found in numerous variations in plants, e.g., in flavonoids (Fig. 4) or tocopherols (Fig. 2). The antioxidant capacity of phenolic compounds includes not only direct scavenging of ROS, but also originates from the abihty of compounds carrying two or more hydroxyl groups to bind transition metal ions. Such chelation strongly decreases the transition metals capability to induce environmental oxidative stress. 

Proestos C, Chorianopoulos N, Nychas G-JE, Komaitis M (2005) RP-HPLC analysis of phenolic compounds of plant extracts. Investigation of their antioxidant capacity and antimicrobial activity. J Agric Food Chem 53 1190-1195... 

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