Prooxidative activity of myoglobin species in linoleic acid emulsions

Initiation of lipid peroxidation in oil-in-water linoleic acid emulsions catalyzed by metmyoglobin (MbFe(III)), metmyoglobin/oxymyoglobin (MbFe(III)/MbFe(II)O-2), ferrylmyoglobin (MbFe(IV)=0), and perferrylmyoglobin (*MbFe(IV)=O) was investigated in the pH area of interest for meat and meat products (pH 5.5-6.5). MbFe(III), MbFe(IV), and MbFe(III)/MbFe(II)O-2 showed similar lipid hydroperoxide dependent catalytic efficiency in initiating lipid peroxidation. The presence of lipid hydroperoxides, in heme protein-initiated Lipid peroxidation, was found to be the crucial factor rather than the redox state of heme proteins. In contrast, *MbFe(IV)=O, formed in situ by reaction of MbFe(III) with H2O2, was an ineffective catalyst, as it undergoes intramolecular electron transfer resulting in heme globin cross-linkage to yield a green iron(III) heme pigment rather than reacting with the lipids.