EFFECT OF SUCROSE ON MILK PROTEIN, LBG AND THEIR INTERACTIONS

Polysaccharides are widely used in the dairy industry as stabilising, thickening and gelling agents and locust bean gum (LBG) is one of the most commonly used. Together with the milk proteins, they form a pseudoternary milk protein-polysaccharide-water solution. The aim of this study was to build up a more detailed thermodynamic and kinetic understanding of molecular interactions between milk protein and LBG and to look especially at the effect of sucrose. Ternary phase diagrams in absence or in presence of sucrose (20, 30 or 40% w/w) were established and compared. For such a system, a very high degree of incompatibility has been demonstrated leading to thermodynamic separation into two distinct phases, one rich in protein and the other in polysaccharide. The similarity of a Skimmed milk (SMP/LBG and a micellar casein/LBG system suggests also that the incompatibility between skimmed milk and LBG is largely attributable to the incompatibility of micellar casein and LBG. Sucrose appears to have only a modest influence on the thermodynamics of these mixed systems, leading to a concentration effect within the protein phase and a dilution within the locust bean gum phase. Data on the effect of sucrose on the individual components suggests, however, an improved solvent effect for LBG. It has been clearly demonstrated that the microstructure of these systems is driven by the phase volume ratio.