Oxidation of Milk Fat Globule Membrane Material. II. Relation of Ascorbic Acid and Membrane Concentrations

Summary The rate of development of oxidized flavor in model systems as influenced by the initial concentration of ascorbic acid was measured by the thiobarbituric acid reaction. At constant fat globule membrane material (FGMM) concentration, the rate of lipid oxidation increased with increasing initial concentration of ascorbic acid up to 20-40mg/liter. Further increases effected inhibition of lipid oxidation in relation to the concentration of ascorbic acid. At constant initial ascorbic acid concentration, the rate of lipid oxidation increased directly with FGMM concentration. The initial reaction rate appears to follow zero-order kinetics over-all. Energy of activation was 11.9 k cal/mole. The rate of ascorbic acid oxidation was proportional to the rate of lipid oxidation. Addition of copper in concentrations 0.1ppm increased ascorbic acid oxidation, but lipid oxidation was further inhibited. It is suggested that the lipid oxidative system is activated by association with ascorbic acid and inhibited by products of ascorbic acid oxidation.