Effect of sucrose on phase and flow behavior of protein-polysaccharide mixtures

The effect of different sucrose levels on phase and flow behavior of two model polysaccharide-protein aqueous two-phase systems (ATPS), Persian gum (PG)-sodium caseinate (NaCas) and sodium alginate (NaAlg)-NaCas, was studied. Phase diagrams were determined and changes in their shape and the actual position of phase boundary features were investigated in the presence of different sucrose concentrations. It was found that the thermodynamic compatibility of mixtures was enhanced by raising the level of sucrose leading to the concentration of protein-rich equilibrium phase and the dilution of polysaccharide-rich equilibrium phase. This was shown to clearly correspond to a decrease in the slope of the tie lines. SDS-PAGE pattern indicated that sucrose had no effect on selective fractionation of NaCas subunits between the equilibrium phases upon de-mixing. The flow behavior of these ATPS was found to depend on the volume ratio and composition of the equilibrium phases. At constant phase volume ratio, increasing sucrose concentration changed the viscosity in accordance with the nature of the continuous phase, whilst at constant composition, rising sucrose level promoted the viscosity and shear thinning behavior.