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Electrophoretic Properties of Casein from Sterilized Milk Stored at Different Temperatures¹

Department of Food Technology, University of Illinois, Urbana

ABSTRACT

High-temperature short-time sterilization of milk did not hydrolyze the proteins but it denatured some serum proteins which were precipitated with the casein, and either moved at the same mobility at pH 8.7 as -casein, or was associated with it and increased the area under the peak. A split in -casein appeared in some cases during storage. Preheating, order of homogenization and storage temperatures, and time affected the relative areas of - and ß-casein from sterile milk. The amount of -casein plus denatured serum proteins did not change greatly during storage for milk preheated at either 140 or 180° F., and homogenized either before or after sterilization. The mobilities varied for -casein from milk preheated to 180° F., homogenized either before or after sterilization; but those for milk preheated to 140° F. and otherwise treated similarly were unchanged. The amount of ß-casein from sterile milks varied with the preheating and storage temperatures and homogenization. The breakdown of ß-casein to a new component, X, with a mobility near that of -casein, and more noncasein and nonprotein nitrogen in milk preheated to 140° F., was greatest at 100, intermediate at 70, and least at 40° F. storage. This breakdown occurred, also, in milk preheated to 180° F., but was insufficient to increase noncasein and nonprotein nitrogen. The breakdown of ß-casein may be caused by a protease.

¹ Funds for this study were supplied by U. S. Public Health Service Research Grant 1947.

² Data were taken from a thesis submitted for the Ph.D. degree, University of Illinois, 1957.