Oxidation of Fatty Acids by

The hemoproteins catalase and peroxidase, after heat treatment which decreased their enzyme activities, became more efficient as heme catalysts of linoleic acid oxidation. These effects might be of importance for preservation and storage of food. Hemoproteins are known to catalyze the oxidation of unsaturated fatty acids by oxygen (1). It has been shown that cooking of meat results in a conversion of ferrohemochrome to ferrihemochrome which might increase the oxidation of tissue fat (2). Other food products which have been heat treated to minimize enzyme action during storage, often develop rancid compounds formed by oxidation of fatty acids. In the case of food from plant sources, this can be ascribed to remaining activities of lipoxygenase, or to small amounts of hemoproteins always present. In order to get information of the role played by hemoproteins in this respect, we investigated the oxidation of linoleic acid by catalase (E.C. 1.11.1.6.) and peroxidase (E.C.I.ll.I.7.), both ferric hemoproteins, that were subjected to heat treatment or acidification followed by neutralization. At the same time, the variations in enzyme activity on hydrogen peroxide were measured. In these experiments ox liver catalase, 39,000 units/mg, (Boehringer) and two preparations of horseradish peroxidase, RZ 1.73 and 3.0 (Worthington) served as sources of the hemoproteins. Concentrations of 0.4" 10 -2 /~mole/ml for catalase and 1.3"10 -2 /~mole/ml for peroxidase in a 0.01 M sodium potassium phosphate buffer at pH 6.5 were used. These concentrations correspond to 1.6"10 -2 and 1.3" 10-2 umole heme/ml, respectively. Heat treatment in increments of 5-10 C was performed by two procedures. For the first one, covering the temperature range 25-95 C a