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The Dry Milk Company, Inc., Research Laboratories, Bainbridge, New York
ABSTRACT
The various data and observations as presented would seem to show that the particular group of substances contributing to the foaming ability of milk is contained in that group of milk constituents commonly designated as the "nitrogenous extractives." Such substances are physically associated with the better classified milk constituents, particularly the proteins. The physico-chemical properties of the highly dispersed and unstable colloids contributing to the foaming property of milk and to the character of milk foam are no doubt responsible for many other physical characteristics and reactions of milk and its derivatives. The reactions manifested by these colloids under the influence of change in hydrogen-ion concentration, salt content of the medium, temperature change, agitation, radiant energy, and aging serve as a basis for assigning to this milk fraction a significant role in many common phenomena with which the dairy chemist and milk technologist is familiar.
It is probable that the lipid material which is associated with the milk proteins and especially with the nitrogenous colloids discussed in this paper contributes not only to the surface-active characteristics of the material with which it is prosthetically bound, but also to the other physical properties exhibited by milk and certain of its derivatives. Direct proof of the presence of a saponin-sterol grouping as a normal constituent of the surface-active substances under consideration is difficult. However, certain evidence would seem to indicate such a possibility. The precise character of the proteinaceous constituent of the material dealt with in these studies cannot be denned in terms of the usual classifications without reservation. Lactoglobulin is strongly suggested by many of its properties; however, irregularities in chemical constitution and many of its physical reactions prevent firm conclusions to this effect.
The conception of prosthetically bound entities or specific groupings which influence or in fact may determine primary reaction characteristics of specimen products such as milk and certain of its constituents, is in conformity with considerable data of recent origin. Such a concept permits an approach to many complicated problems prevalent in the milk industry which is impossible from a strictly analytical point of view. In a previous paper from these Laboratories (13) it was shown that certain biological activities exhibited by milk constituents may be due to a prosthetically bound complex involving the milk proteins, especially the lactalbumin, and cholesterol.
In considering the various observations recorded in this paper from a purely biochemical standpoint the colloidobiological study of the vitamins by von Hahn (14) should be mentioned. The author considers vitamin activity in parallel with surface-activity. The activation and inhibition of certain enzymes may be dependent upon capillary-activity, as Glick and King (15) have recently reported. In all probability digestion, assimilation, and elimination are influenced by surface-active substances. Notwithstanding the speculative possibilities concerning the relationship between the surface-active properties of milk substances and physiological matters, it is reasonably certain that such properties exhibited by segregated milk constituents indicate their potential rôle in affecting many phenomena commonly observed in the milk industry.
* Presented at the 29th Annual Meeting of The American Dairy Science Association, June 27, 1934, Ithaca, N. Y.
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