Changes in myoglobin due to lipid oxidation were studied in a model system, consisting of a mixture of metmyoglobin and methyl linoleate (2:1), which was mechanically emulsified, freeze-dried and stored at 37°C. After storage, samples were reconstituted, centrifuged and lipid fractions were separated and tested for degree of oxidation. The protein was recovered in two fractions: “soluble fraction” (supernatant) and “aggregates” (precipitated proteins). Absorption spectroscopy confirmed protein insolubilization due to formation of aggregates. SDS-PAGE of metmyoglobin recovered from both fractions indicates gradual formation of covalently bound polymers upon storage. Isoelectric focusing (IEF) shows formation of new bands and zones with a drastic acidic shift of isoelectric points. Two-dimensional IEF/SDS-PAGE shows that the newly formed bands on IEF correspond to covalently bound myoglobin polymers.