CATALYSTS OF LIPID PEROXIDATION IN MEATS. 2. Linoleate Oxidation Catalyzed by Tissue Homogenates

SUMMARY In beef tissue homogenate, both types of catalysts—hemoprotein and non‐heme iron–are active catalysts of linoleate oxidation. Although the pH‐dependent catalytic pattern of beef homogenate was similar to MetMb catalysis, the presence of non‐heme iron could be identified by adding ascorbate or 8‐OH‐quinoline. Ascorbate‐stimulated oxidation could be inhibited by chelating agents. Furthermore, lower concentrations of phosphate buffer rendered the non‐heme iron more active at acidic pH. Linoleate oxidation was also catalyzed by H 2 O 2 ‐treated (heme‐free) beef homogenates. Oxidation was accelerated either by thiols or by ascorbate. Both EDTA and 8‐OH‐quinoline abolished catalysis, but xanthine and citric acid further accelerated. An active non‐heme iron chelate thus is indicated. In shrimp tissue homogenate, the evidence suggested that non‐heme metal complexes were playing a dominant role in catalysis. Except for the anomalous behavior of thiols, the effect of pH changes and various additives was similar to that in Fef(II)‐EDTA model systems.