CATALYSTS OF LIPID PEROXIDATION IN MEATS. 3. Catalysts of Oxidative Rancidity in Meats

SUMMARY Data presented in this paper can be interpreted as evidence that both heme and non‐heme iron are functioning as catalysts of lipid oxidation in meat. The most direct evidence comes from cooked meat, since there the picture is not complicated by interfering enzymes. After removal of MetMb by treating with H 2 O 2 , a significant lipid oxidation was demonstrated, especially at lower pH where non heme iron is most active. The catalytic activity of hemoprotein is limited in raw meat. Oxygen can be removed from the tissues and MetMb reduced back to Mb by the reducing enzymes. This is especially true at higher PH. Possible limitations of the heme‐catalyzed reactions in meat by high (inhibition) levels of myoglobin, or because of separation of reactants in cellular structures, are discussed. The effects of additives were in line with the interpretation that lipid oxidation is catalyzed by both non‐heme and hemoprotein. In raw meat, lipid oxidation could be slightly accelerated by adding TDPA or cysteine but inhibited by adding ascorbic acid or EDTA. It is considered that EDTA inhibited the non‐heme iron catalysis at the natural acidic pH, whereas ascorbic acid prevented Mb oxidation and thus indirectly retarded the rancidity developed.