Heat induced formation of beta-lactoglobulin microgels driven by addition of calcium ions

Stable suspensions of spherical protein particles (microgels) can be formed by heating beta-lactoglobulin solutions in the presence of calcium ions. The conditions for the calcium induced microgel formation were studied at different pH between 5.8 and 7.5 and different protein concentrations between 5 and 100 g/L after heating at 85 degrees C for 15 h. The results showed that a critical molar ratio of calcium to proteins (R) is needed to form microgels independent of the protein concentration. R decreases with decreasing pH. The microgels have a hydrodynamic radius ranging from 100 to 300 nm and their internal protein concentration ranges from 0.2 to 0.45 g/mL. The amount of calcium bound to the proteins was determined and the results suggest that the crucial parameter for microgel formation is the net charge density of the native proteins. The microgel suspensions are stable in a narrow range of R but the microgels aggregate at higher calcium concentrations. (c) 2012 Elsevier Ltd. All rights reserved.