Effect of solvent and certain food constituents on different antioxidant capacity assays

The effect of the sample solvent in the antioxidant capacity of foods measured by the four most widely used procedures (ABTS, FRAP, DPPH and ORAC) has not been systematically studied. This was the aim of this work. The antioxidant capacity of catechin:gallic acid solutions in different solvents (water, methanol/water, methanol, acetone/water) were determined. Significant differences were found between the values obtained by the same method in different solvents, as well as between the ones obtained by the different method in the same solvent (ranging from 10,000 to 30,000 μmol Trolox/g dw). In addition, certain non-antioxidant food constituents, such as amino acids and uronic acids, also showed an interfering effect on these assays. ORAC was the assay in which all these factors had a greatest interfering effect. Antioxidant capacity values should only be compared when the measurements have been made by the same method in the same solvent.