Modelling ion composition in simulated milk ultrafiltrate (SMUF) II. Influence of pH, ionic strength and polyphosphates

This study aims to determine whether the dynamic ion speciation (DIS) model, as introduced in part I, can predict the ion composition in freshly prepared simulated milk ultrafiltrate (SMUF) under various conditions, e.g. pH, ionic strength and presence of various polyphosphates. Experiments were carried out in freshly prepared SMUF enriched with different salts. The model predictions were in satisfactory agreement with experimental results for all conditions. Moreover, specific ion effects were taken into account in the model, where sodium ions were not counted as equivalent to potassium ions due to differences in hydration properties. Polyphosphates, in particular sodium hexametaphosphate (SHMP), were well integrated into the DIS model with reasonable association constants and solubility products. The DIS model suggests that SHMP displays chain polyphosphate properties, which provides better understanding of its interaction with cations. The DIS model appears to be a robust and versatile tool to describe ion equilibria in SMUF.