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Effect of Heat on the Centrifugal Sedimentation of Milk Serum Proteins

Dairy and Meat Laboratory, Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture, Washington, D. C.

ABSTRACT

Some diversity of opinion exists among investigators regarding the effect of heat on the subsequent removal of the milk serum proteins by high-speed centrifugation. There appears to be agreement, however, that no significant amount of serum proteins in raw skimmilk is removed by a centrifugal force of about 30,000 times gravity for periods of up to 1 hr. Ramsdell and Whittier (3) centrifuged heated and unheated skimmilk for various periods of time in an air-driven, bowl-rotor ultracentrifuge (2), analyzed the supernatant liquid, and plotted the grams of acid-coagulable nitrogen per 100 g. of liquid against total nitrogen. They interpreted the parallelism of the lines for heated and unheated milk to mean "that no albumin or globulin was thrown out" under their conditions of centrifuging, and that "these whey proteins were not coagulated." The difference between the two lines was constant at about 0.09% nitrogen.

This represents the heat-denatured serum proteins, which are determined by the difference between the acid-precipitable fractions in heated and unheated milk.