CATALYSIS OF LIPID OXIDATION: A STUDY OF MULLET (Mugil cephalus) DARK FLESH AND EMULSION MODEL SYSTEM

Abstract

ABSTRACTThe dark flesh of mullet (Mugil cephalus) was compared with beef muscle for total iron, total hemoprotein, and total nonheme iron. Mullet dark flesh contained 57.3 ppm iron, over twice the amount in beef, 26.0 ppm. Total possible nonheme iron content of mullet dark flesh ranged from 56–75%, compared to 11–29% for beef. In a linoleate emulsion model system, mullet dark flesh homogenate was analyzed for heme and nonheme iron activity as lipid oxidation catalysts. Addition of ascorbic acid, EDTA, and cyanide, at different pH levels, indicated the nature of the catalyses. Of the additives, cyanide yielded the strongest inhibition on a molar basis. Based on the criteria of other researchers, these data suggest that heme iron is the major catalyst of lipid oxidation in mullet flesh. The rates of O2 uptake by mullet dark flesh homogenate and by Fe/EDTA increased with increasing acidity, rather than exhibiting a previously reported peak at pH 5.5. The latter appears to be a phenomenon of limited occurrence rather than a general test criteria. In light of this finding, the nature and nomenclature of biological nonheme iron is discussed.