Some Factors Affecting the Stability of Certain Milk Properties. VII. The Effects of Metals and of Ascorbic Acids on the Oxidation-Reduction Potential

Abstract

Summary The effect of soluble metals, oxygen, hydrogen, and ascorbic acids on the oxidation-reduction potential of milk has been studied. The addition of copper (copper sulfate solution) to milk caused an increase in the oxidation-reduction potential, the speed of increase and the magnitude reached depending upon the concentration of copper. With the higher concentration of copper the maximum potential was reached in a relatively short time, and this level was maintained throughout the storage period. Milks to which ferrous iron was added had lower potentials at the end of 48 hours than at the beginning, but the ferrous iron maintained a potential slightly above that of the control sample. This observation is not in agreement with reports of other investigators. Nickel sulfate and ferric, vanadium, aluminum, manganese, chromium, and stannous chlorides, when added in concentrations of 10 -5 , 4×10 -5 , and 10 -4 moles per liter of milk, did not alter significantly the potential from that of the control sample. Partial removal of dissolved oxygen by evacuation lowered the potential of milk to which no copper was added and definitely limited the increase in potential of milk to which copper was added. Bubbling hydrogen gas through milk greatly lowered the potential. On storage, however, the potential increased to an E H of about O, at which point equilibrium was apparently established. Addition of copper to the hydrogen-treated milk did not significantly affect the potential. The addition of synthetic crystalline ascorbic acids greatly decreased the potential, the amount of decrease depending upon the concentration added. Addition of both soluble copper and synthetic ascorbic acids to the milks caused a subsequent rise in potential, the magnitude and rate of increase depending upon both the concentration of acid and the concentration of copper added. The milks containing the greater concentration of ascorbic showed a lesser rise in potential upon the addition of a given amount of copper. Very little difference was observed between the influence of levoascorbic acid or of dextro-isoascorbic acid on the potential either in the presence or the absence of added soluble copper.