Phase separation of a milk protein and guar gum: The effect of guar gum molecular weight and oil addition on the phase diagram
Wentao Liu, Tim Foster
Abstract
Skimmed milk powder (SMP), and low and high molecular weight guar gum (GG), were used to establish phase diagrams at 5 °C and pH 6.5 to better understand the phase behaviours of the milk protein/guar gum systems. As expected, the compatibility of SMP-GG system was found to increase with decrease in molecular weight of the GG. Confocal laser scanning microscopy (CLSM) clearly shows that the microstructure was dependant upon starting composition which in turn determines the relative phase volumes of the two phases. This phase separated microstructure of SMP-GG can be considered as a water-in water (W/W) emulsion. Through the incorporation of oil into these systems with designed microstructures based on the phase diagram, it is possible to form a model systems of SMP-GG-OIL, showing a lipid phase within a protein phase within a polysaccharide phase, which can be described as ‘Matryoshka Composites’ and therefore being viewed as ‘O/W/W’ emulsion when the starting aqueous phase is either polysaccharide continuous or bi-continuous. The addition of low volume fraction of oil has indicated an influence on the thermodynamic equilibrium of SMP-GG system, through chemical analysis and rheological measurement. This probably leads to a tie-line change in the established phase diagram of SMP-GG system.