Pro- and antioxidative activity of protein fractions from pork (longissimus dorsi)

Protein fractions from pork (longissimus dorsi), isolated in search of the factor in meat enhancing non-heme iron absorption, have been analysed for their effect on radical formation and oxidation processes. In heat-treated minced meat samples with the protein fractions incorporated, the water-soluble proteins showed a prooxidative effect on lipid oxidation compared to the salt-soluble and the insoluble proteins, which did not influence oxidation in the meat system relative to control samples. The level of secondary oxidation products in meat samples with water-soluble proteins added was, however, not as high as would be expected from the ability of this protein fraction to initiate oxidation as measured by spin-trapping ESR-spectroscopy in meat emulsions and by oxygen depletion rates in a lipid model system with the protein fraction added. In agreement with this observation, the water-soluble protein fraction was found, in addition to being prooxidative, also to have the highest antioxidative potential of the three protein fractions as measured by spin probing ESR-spectroscopy (Fremy's salt method). The prooxidative activity of the water-soluble proteins was assigned to myoglobin and hemoglobin derivatives (detected spectrophotometrically), emphasising the role of iron-catalysis in oxidative deterioration of meat products.