Modelling ion composition in simulated milk ultrafiltrate (SMUF). I: Influence of calcium phosphate precipitation

摘要

Freshly prepared simulated milk ultrafiltrate (SMUF) is a solution that is supersaturated with respect to various calcium phosphate phases that precipitate in time. As a consequence, the ion composition of equilibrated SMUF was found to be significantly different from that of freshly prepared SMUF. This study proposes a thermodynamic ion-speciation model that is able to describe ion equilibria in SMUF. Moreover, it is also able to describe calcium phosphate precipitation in Fresh SMUF on its way to equilibrium by using an apparent solubility product for CaHPO_4·2H_2O as a function of time. The model was validated by experiments in which CaCl_2 and Na_2HPO_4 were added to freshly prepared SMUF. The changes in calcium activity and pH were followed and the precipitates were characterised by X-ray diffraction. The model was able to predict the observed changes.