STUDIES ON OXIDATION-REDUCTION IN MILK I. OXIDATION-REDUCTION POTENTIALS AND THE MECHANISM OF REDUCTION

Publisher Website
Google Scholar
Abstract
Potential-time curves of milk and milk-methylene blue mixtures are given. The positive Eh limits of all the milks lay between +0.2 and +0.3 volt. The negative potential limits reached by all the milks here reported approximated Eh[long dash]0.2 volt, due, it is suggested, to the predominating influence of Streptococcus laciis. The range of reduction of methylene blue in milk was observed to be more positive than the theoretical value at this pH, and varied considerably in different milks. An explana- tion is suggested for the upward trend of the potential curve sometimes noted after the negative limit is reached. The "poising" effect of methylene blue in the standard concentration in milk is so small as to be almost negligible. The role of H in reduction is discussed, and the effect of some substances on reduction times is shown, as well as the effect of cysteine on potentials in milk. The role of O is discussed and evidence presented of its relation to reduction and to reduction potentials The necessity for revision of enzyme concepts is made apparent and attention is drawn to the need for consideration of the reducing properties of bacteriological media. All of this work tends to confirm the theory of Barthel, that the disappearance of methylene blue in the reduction test in milk takes place in 2 stages: removal of the dissolved O by bacteria; reduction of the dye by constituents of the milk. Evidence is brought forward to show that the reducing "capacity" of raw milk is sufficient to reduce a concentration of methylene blue of 1 part of dye to 100,000 parts of milk in approximately the same time as in the standard concentration, 1:200,000. The "capacity" of heated milk is sufficient to reduce this dye in a concentration as high as 1:1000. The rate of reduction of methylene blue in raw milk is rapid and depends on the speed with which the potential passes through the range of this dye. The time taken for reduction of the dye in normal raw milk is usually short in comparison with that necessary for O consumption.