Effects of solvent and alkaline earth metals on the heat-induced precipitation process of sodium caseinate

The precipitation temperatures of sodium caseinate in H2O and D2O in the presence of Mg2+, Ca2+, Sr 2+ and Ba2+ were investigated through fluorescence, turbidity and conductivity experiments. As for the ability of the divalent cations (1-17.5 mM) to induce the precipitation process in H2O, the sequence Ba2+ ≥ Ca2+ > Mg2+ > Sr 2+ was found. Remarkably, while at low salt concentrations (<10 mM) precipitation temperatures (TPs) were found to change significantly depending on the specific cation, at higher concentrations (>10 mM) the differences among the different cations were greatly reduced. By fitting these results with a modified Jones-Dole equation, we confirmed that the less hydrated ions possess a greater capacity to induce precipitation. In D2O, the order of ion ability to induce caseinate precipitation was Ba2+ > Ca2+ > Sr2+ > Mg2+. The different hydrophobicity between D2O and H2O was shown to affect significantly the TPs of caseinate in the presence of calcium, strontium and barium.