Reduction of ferrylmyoglobin by dietary phenolic acid derivatives of cinnamic acid

The reaction of dietary phenolic acid derivatives of cinnamic acid with high valence states of horse myoglobin was studied. When metmyoglobin was oxidized by hydrogen peroxide (H2O2) in the presence of the phenolic acids, ferrylmyoglobin was reduced to metmyoglobin. However, addition of the phenolic acids to a ferrylmyoglobin solution resulted in a modified metmyoglobin spectrum characterized mainly by a blue shift of the 631 nm peak and a new isosbestic point at 613 nm suggesting an irreversible modification of the hemeprotein. The efficiency and the kinetic profile of ferrylmyoglobin reduction were dependent on both the concentration and the structure of the phenolic acid. Electron-donating substituent groups in the phenol ring increased the efficiency of ferrylmyoglobin reduction whereas electron-withdrawing groups decreased it. The phenolic acids exhibiting a catechol structure were the most efficient in reducing ferrylmyoglobin. Caffeic and chlorogenic acids react faster than trolox, and caffeic acid faster than ascorbate. During the electron-transfer reactions, the phenolic acids were oxidized to quinoid forms and, in some cases, to polymer products as indicated by comparison of the ultraviolet (UV) spectra obtained in the presence of metmyoglobin/H2O2 with those recorded after oxidation of phenolic acids by horseradish peroxidase/H2O2 and catechol oxidase. The results suggest that dietary phenolic derivatives of cinnamic acid may counteract deleterious oxidations initiated by ferrylmyoglobin.