CHROMATOGRAPHIC ELUTION PROFILES, ELECTROPHORETIC PROPERTIES AND FREEAMINO AND SULFHYDRYL-GROUP CONTENTS OF COMMERCIAL SODIUM CASEINATES

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 profil es showed that the charged residues of constituent proteins in the cas einates were modified to different extents. Commercial caseinates show ed an extra peak (pre-alpha(s1)-casein) on cation exchange FPLC, which eluted at a lower salt concentration than that required to elute alph a(s1)-casein; there was little pre-alpha(s1)-casein in the laboratory- prepared caseinate. Gel permeation FPLC showed that the caseinates con tained different levels of high molecular weight proteins which were p resent at very low levels in the laboratory-prepared caseinate. Alkali ne urea-PAGE gave good resolution of all proteins in the laboratory-pr epared caseinate while in the commercial caseinate samples, protein ba nds were smeared and alpha(s2)-casein was less pronounced. The laborat ory-prepared caseinate had a higher content of free amino and sulphydr yl groups than the commercial caseinates. (C) 1997 Elsevier Science Lt d.