Chromatographic elution profiles, electrophoretic properties and free amino and sulphydryl group contents of commercial sodium caseinates

Abstract The proteins in commercial sodium caseinates and laboratory-prepared, unheated sodium caseinate were studied using anion and cation exchange FPLC, gel permeation FPLC and alkaline urea-PAGE, and free amino and sulphydryl groups were analysed. Anion and cation exchange FPLC profiles showed that the charged residues of constituent proteins in the caseinates were modified to different extents. Commercial caseinates showed an extra peak (pre-αs1-casein) on cation exchange FPLC, which eluted at a lower salt concentration than that required to elute αs1-casein; there was little pre-αs1-casein in the laboratory-prepared caseinate. Gel permeation FPLC showed that the caseinates contained different levels of high molecular weight proteins which were present at very low levels in the laboratory-prepared caseinate. Alkaline urea-PAGE gave good resolution of all proteins in the laboratory-prepared caseinate while in the commercial caseinate samples, protein bands were smeared and αs2-casein was less pronounced. The laboratory-prepared caseinate had a higher content of free amino and sulphydryl groups than the commercial caseinates.