REDUCTION OF FERRYLMYOGLOBIN BY DIETARY PHENOLIC-ACID DERIVATIVES OF CINNAMIC ACID

The reaction of dietary phenolic acid derivatives of cinnamic acid wit h high valence states of horse myoglobin was studied. When metmyoglobi n was oxidized by hydrogen peroxide (H2O2) in the presence of the phen olic acids, ferrylmyoglobin was reduced to metmyoglobin. However, addi tion of the phenolic acids to a ferrylmyoglobin solution resulted in a modified metmyoglobin spectrum characterized mainly by a blue shift o f the 631 nm peak and a new isosbestic point at 613 nm suggesting an i rreversible modification of the hemeprotein. The efficiency and the ki netic profile of ferrylmyoglobin reduction were dependent on both the concentration and the structure of the phenolic acid. Electron-donatin g substituent groups in the phenol ring increased the efficiency of fe rrylmyoglobin reduction whereas electron-withdrawing groups decreased it. The phenolic acids exhibiting a catechol structure were the most e fficient in reducing ferrylmyoglobin. Caffeic and chlorogenic acids re act 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 aci ds by horseradish peroxidase/H2O2 and catechol oxidase. The results su ggest that dietary phenolic derivatives of cinnamic acid may counterac t deleterious oxidations initiated by ferrylmyoglobin.