Stability of milk-derived calcium phosphate suspensions

Abstract

Milk-derived calcium phosphate (MDCP) can be isolated from whey derived from acid casein or cottage cheese manufacture as a precipitated calcium phosphate material. However, the composition and suspension properties of this MDCP material are poorly understood. This study was aimed at examining the properties of MDCP when in suspension, and the factors affecting the stability of this calcium phosphate suspension. When suspended in water, MDCP aggregated, with the aggregation rate increasing with increasing temperature. Aggregation was more rapid in milk permeate than in water. The aggregation of MDCP increased with increasing ionic strength, and, as this was accompanied by a decrease in the magnitude of the ζ-potential, this could be explained by the effects of the electrolyte concentrations on the electrical double layers of the particles. Soluble calcium markedly increased the rate of aggregation of the MDCP, whereas soluble phosphate slightly retarded the aggregation. Soluble calcium changed the ζ-potential from negative to positive, with the particles becoming progressively more positive at higher soluble calcium levels. In contrast, increasing soluble phosphate levels made the ζ-potential of MDCP particles markedly more negative. These results indicate that the addition of soluble calcium or soluble phosphate had more specific effects, probably binding to the surface of the MDCP particles. The increased rate of aggregation in soluble calcium solutions could not be solely explained by the changes to the ζ-potentials of the particles.