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Effect of Heating, Cooling, and Storing Milk on Casein and Whey Proteins

Department of Food Science, Cornell University, Ithaca, NY 14853

ABSTRACT

Cottage cheese yields increase as a result of heating (74°C, 10 s), cooling (3°C), and storing (7 days) milk prior to cheese making. Protein analysis of milk indicated that casein was higher and whey proteins lower in experimental heated, cooled, stored milk as compared with unheated, fresh (<2 days old) control milk. Heating caused some proteins normally in whey to associate with casein by some undetermined mechanism. Samples of control and experimental milk subjected to centrifugation (21,000 x g/120 min) and gel electrophoresis showed that soluble ß-casein decreased with heat treatment and cold storage of milk.

Pretreating raw milk with nitrogen-ethylmaleimide or ethylenetetraacetic acid prior to heat treatment and storage and subjecting these samples to electrophoresis indicated little or no decrease of whey proteins compared with milk heated without added nitrogen-ethylmaleimide or ethylenetetraacetic acid. Heat-treating, cooling, and storing milk seemed to cause part of the ß-casein to be trapped physically in the casein micelle. These treatments also caused portions of whey proteins to associate with casein micelles via disulfide bridging and calcium linkages.

¹ Oberlin Farms Dairy, Inc., 310 Chester Street, Painesville, OH 44077.