Oxidation of myofibrillar proteins induced by peroxyl radicals: Role of oxidizable amino acids.

During storage and processing of foods, myofibrillar proteins (MP), the most abundant proteins of meats, are exposed to peroxyl radicals (ROO). The present work shows that ROO induce oxidation of MP leading to a widespread of MP aggregation. In spite of the extent of such process, only partial consumption of the more oxidizable amino acids was determined. MP were exposed to ROO derived from thermolysis of AAPH (2,2'-azobis(2-methylpropionamidine) dihydrochloride), and samples studied through SDS-PAGE, western blotting, light scattering, time-resolved fluorescence, and high performance liquid chromatography. Together with MP aggregation, consumption of methionine (the most consumed residue), cysteine, tyrosine, and tryptophan were determined. These results are associated with conformational changes of MP affecting the accessibility of tryptophan residues to the solvent, as evidenced by a decreasing of its fluorescence lifetime. Lysine residues, which are not reactive towards ROO, were also consumed, suggesting participation of Schiff bases in the MP aggregation process.