Effect of heat denaturation on the pro-oxidative activity of metmyoglobin in linoleic acid emulsions

To reveal the effect of heat denaturation on the pro-oxidative activity of MMb, the thermal denaturation of metmyoglobin (MMb) was investigated using differential scanning calorimetry (DSC) and UV-vis spectrometry in combination with an investigation of the pro-oxidative activity of heat-denatured MMb in linoleic acid emulsions, as registered by oxygen consumption. Thermograms of MMb solutions obtained using DSC and progress curves of the absorbance changes at 290, 409, and 540 nm during heating showed that temperatures immediately below thermal denaturation of MMb-induced structural changes in the heme protein which subsequently increased the pro-oxidative activity of the molecule. In contrast, temperatures above the denaturation temperature of MMb decreased the pro-oxidative activity of the resulting species compared to native MMb. The decrease in pro-oxidative activity was found to be related to hemichrome formation. Moreover, the amount of free iron released during heat denaturation of MMb was measured and found to be of an order where it would not be expected to play any significant role as an overall pro-oxidant in the initial phase of lipid peroxidation in the presence of other pro-oxidative species formed during heat denaturation of MMb. The latter could be concluded from a comparable study of the catalytic activity of free iron(II), hemin, MMb, and heat-denatured MMb in Linoleic acid emulsions. Finally, heat treatment of MMb and the pro-oxidative activity of resulting species are discussed with regard to possible influence on oxidative stability of meat.