AN IMPROVED PROCEDURE FOR THE PRELIMINARY FRACTIONATION OF MILK-PROTEINS

Skim milk was directly subjected to fractionation by a procedure based on differential solubilities; fractions obtained were examined by polyacrylamide gel electrophoresis. Fractionation of skim milk in 50% (v/v) ethanol containing 0.4 M NaSCN and 0.15 M CaCl2 yielded a precipitate consisting of its major protein components mid a supernatant consisting principally of gamma-caseins and alpha-lactalbumin. The precipitate was further fractionated in a urea-Ca phosphate system to yield a soluble fraction containing kappa-casein and beta-lactoglobulin and an insoluble fraction composed of calcium-sensitive caseins (alpha(s1), alpha(s2), and beta-caseins). These fractions may be used as sources for the separation of individual milk proteins.