Assessing the antioxidant and pro-oxidant activity of phenolic compounds by means of their copper reducing activity

The antioxidant or pro-oxidant activity of some dietary phenolic compounds has been determined by their reducing activity over Fe3+ and Cu2+. The FRAP method has shown that phenolic acids exert a high reducing activity that give rise to a decrease in linoleic acid oxidation mediated by Fe3+, measured as TBARS. However, the reducing activity of phenolic compounds over Cu2+ leads to linoleic acid oxidation. Reducing capability against copper has been measured by a new approach called CRAI (Copper Reducing Activity Index), and results agreed with the degree of hydroxylation of the studied compounds. Sensibility and reproducibility of the method have been checked by measuring the inter-day and intra-day variation (1.08 and 1.89%, respectively). Possible pro-oxidant activity of phenolic compounds should be considered when the overall antioxidant activity in Cu naturally rich or Cu-enriched foodstuffs for dietetic purposes has to be evaluated.