Electrophoretic Properties of Casein from Sterilized Milk Stored at Different Temperatures

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 [alpha]-casein or were associated with it and increased the area under the peak. A split in a-casein appeared in some cases during storage. Pre-heating, order of homogenization and storage temperatures and time affected the relative areas of [alpha]- and [beta]-casein from sterile milk. The amount of [alpha]-casein plus denatured serum proteins did not change greatly during storage for milk pre-heated at either 140[degree] or 180[degree] F, and homogenized either before or after sterilization. The mobilities varied from [alpha]-casein from milk pre-heated to 180[degree] F, homogenized either before or after sterilization, but those for milk preheated to 140[degree] F and otherwise treated similarly were unchanged. The amount of [beta]-casein from sterile milks varied with pre-heating and storage temperatures and homogenization. The breakdown of B-casein to a new component X, with a mobility near that of [gamma]-casein, and more non-casein and non-protein nitrogen in milk pre-heated to 140[degree] F, was greatest at 100[degree], intermediate at 70[degree], and least at 40[degree] F storage. This breakdown occurred, also, in milk pre-heated to 180[degree] F, but was insufficient to increase non-casein and non-protein nitrogen. The breakdown of [beta]-casein may be caused by a protease.