Oxidation potentials of caffeic and chlorogenic acids, and their co-pigments with an anthocyan molecule, malvin, were measured by cyclic voltamemetry. It was found that these acids show electrochemical activity in a wide range of pH values of the supporting electrolyte, and that they undergo a similar mechanisms of electrode oxidation. The oxidation potential values indicated good antioxidative properties found with these acids. It was concluded that the antioxidative effect of molecules depend on the pH and on the structure, i.e. the number and position of hydroxyl groups in molecules, as well. The pK-values of the acids determined spectrophotometrically corresponded to pH ranges in which deprotonation processes influence the electrochemical mechanism. The co-pigments formed from malvin and the acids investigated showed better 'antioxidative properties' than pure malvin, but they were somewhat weaker than those for pure acids. (C) 2003 Elsevier B.V. All rights reserved.