The mechanisms of interaction between coffee components and free radicals will also depend on a combination of differences in the molecular structures of antioxidant components and the chemical characteristics of free radicals that are involved in the assay system. Free radicals vary in terms of relative affinity for interacting with atoms that have the highest electron density. The peroxyl radical used for ORAC testing interacts with chlorogenic acid at hydroxyl groups attached to the carbon atom with the largest electronic density in the benzene ring. This is different to the ABTS radical, for which interaction with chlorogenic acid depends on the degree of ionization with carboxyl and phenolic hydroxyl groups.