An improved method for the quantitative fractionation of casein mixtures using ion-exchange chromatography

A method for the quantitative analysis of casein mixtures is described. The method uses ion-exchange chromatography at 4 °C on DEAE cellulose, Whatman DE52 in the presence of tris-chloride-urea buffer (pH 8·6), and a NaCl gradient to fractionate the alkylated casein mixtures and a micro-biuret technique to determine protein concentrations. Values for fractions representative of (1) γ-caseins, (2) κ-casein plus some unknown proteins, (3) β-casein, (4) minor α s -caseins and (5) α s1 - plus α s0 -caseins were obtained, and whole casein from herd bulk milk was found to consist on average of about 2, 13, 36, 11 and 38% respectively of these fractions. Agreement between duplicate fractionations was satisfactory and the recovery of material varied between 94 and 98%.