Phase separation in mixtures of polysaccharides and proteins

Abstract

The phase behaviour of mixtures of proteins and polysaccharides has been investigated to identify the factors controlling phase separation, the ultimate aim being to achieve protein separation. Three proteins, bovine serum albumin (BSA), γ-globulin and lysozyme were mixed with various uncharged polysaccharides to establish conditions under which phase separation occurred. It was found that separation occurred most easily at the isoelectric point (iep) and at lower polymer concentration with increasing polymer molecular mass. At the iep of both BSA and γ-globulin, increasing electrolyte increased the protein solubility, contrary to predictions of classical DLVO theory. This is probably due to the presence of a patch-like distribution of charges on the protein surface. The phase separation could be qualitatively modelled using a depletion flocculation theory.