Betty M. Watts

A distillation method for the quantitative determination of malonaldehyde in rancid foods

SummaryAn improved distillation method is described for the quantitative determination of malonaldehyde in foods containing oxidized fats. The procedure is compared with other methods in current use for the determination of malonaldehyde. A high correlation of TBA numbers with rancid odor in cooked meats was established.

Oxidative Rancidity and Discoloration in Meat

Publisher Summary This chapter is concerned with two types of oxidative changes that occur in meat: oxidation of the fat, resulting in rancidity; and oxidation of the heme pigments, resulting in discoloration. The two are closely related. In fact, each can accelerate the other, but each can also proceed independently of the other. Together they account for a large part of the economic loss due to substandard or spoiled meat. The chapter devotes to the more fundamental work on these reactions and their interrelationships in meat as it is believed that control can best be achieved when the causes of deterioration are thoroughly understood. In general, the oxidative changes discussed are those of chemical rather than microbiological origin, although it is recognized that the same changes are often brought about by bacteria, and it is not always possible to determine whether bacteria are implicated. The chapter presents facts that contradict simple assumptions such as the idea that the fresh meat of any species is a more or less uniform starting point for experimentation and the idea that the various oxidations that occur in meat, resulting in off-odors, off-flavors, and discolorations, could be lumped together for purposes of control.

Acceleration and inhibition of lipid oxidation by heme compounds

The acceleration and inhibition of unsaturated fatty acid oxidation by heme compounds was followed in model systems with an oxygen analyzer. The linoleate to heme molar ratios for maximum catalysis were 100 for hemin and catalase, 250 for metmyoglobin, 400 for cytochrome c and 500 for methemoglobin. With heme concentrations of 2 to 4 times the optimum catalytic amount, no oxidation occurred. Rapid heme destruction was observed with catalyzing ratios of lipid to heme, but with inhibitory ratios a stable red compound formed, believed to be a lipid hydroperoxide derivative of the heme. The ratios of lipid to metmyoglobin for maximum acceleration varied with the pH. Linolenate was much less sensitive to heme catalysis than linoleate. Colorless products of heme degradation had a marked antioxidant effect. A possible mechanism for the antioxidant effect of hemes is advanced, based on the formation of stable heme peroxide complexes or stable heme radicals, or both, during the early stages of oxidation. Prooxidant activity is believed to occur only when the peroxide to heme ratio is so high that the oxidation of the hemes goes beyond the initial stages.