Factors Affecting the Heat Aggregation of Proteins in Selected Skimmilk Sera

Abstract

A simple, low-speed (1,000 × g) centrifugal method was developed and utilized to determine the protein destabilization in acid-prepared (pH 4.6) and ultracentrifugal skimmilk sera heated at temperatures up to 118 C. The serum proteins in acid-prepared serum were much less stable to heat than those in ultracentrifugal serum. Special pH-dialysis treatments, which lowered the calcium phosphate content of acid-prepared serum, reduced the amount of heat-induced protein destabilization. A colloidal phosphate-free (CPF) serum was developed in which the proteins responded to heat in a manner similar to those in skimmilk. Addition of whole casein and various casein fractions to skimmilk sera increased the stability of the proteins to heat, and all casein additives were found to be equally effective. Sephadex G-100 gel filtration results showed that heating acid-prepared serum caused aggregation and destabilization of each of the three protein components; whereas, heating ultracentrifugal serum caused the formation of substantial amounts of intermediate-sized, stable protein aggregates. Heat-induced changes in the elution patterns for these systems agreed well with the centrifugal method results for protein destabilization. © 1964, American Dairy Science Association. All rights reserved.