Effect of temperature and pH on salts equilibria and calcium phosphate in bovine milk

The changes in salt partition and the phase identification of non-diffusible calcium phosphate in bovine milk were studied at different temperature and pH upon heat treatment. As temperature and pH increased, the concentrations of serum Ca, inorganic phosphate (Pi) and citrate decreased, suggesting the formation of calcium phosphate materials. Besides, after heating at 100 degrees C the maximum buffering of milk occurred at pH 4.7 rather than pH 5.1, indicating that the newly formed calcium phosphate materials were chemically different from native micellar calcium phosphate (MCP). According to infrared spectrum, the calcium phosphate formed after high-heat treatment was likely to be alkaline salt, rather than acidic salt as native MCP was. Furthermore, high-heat treatment also resulted in significant increases in the average particle size and zeta potential of casein micelles, possibly due to crosslinks between caseins induced by decreases in electrostatic repulsion and steric effects of kappa-caseins. (C) 2020 Published by Elsevier Ltd.