Natural Variation of Milk Serum Proteins as a Limitation of Their Use in Evaluating the Heat Treatment of Milk

Abstract
Eighty-one samples of fresh bulked milk, collected in 10 regions of the United States in winter, spring, and fall seasons, were analyzed for N distribution, sulfhydryl content, and susceptibility of the serum proteins to heat denaturation. The variability of content of serum proteins and in their heat denaturability imposes serious limitations on the use of serum protein analyses for assessing dry milks of unknown history for specific uses. The sulfhydryl content not only exhibits a natural variability but is further affected by aging of the milk and contamination with Cu.