Calcium phosphate precipitation during concentration by vacuum evaporation of milk ultrafiltrate and microfiltrate

• Two real dairy liquids (UF and MF) were studied.
• A pilot-scale falling-film evaporator close to those used in industry was used.
• Experimental and theoretical approaches to understand calcium phosphate were used.
• Calcium phosphate precipitates differently during evaporation of UF or MF.
• Whey proteins present in MF interact with the precipitate of calcium phosphate.

Vacuum evaporation is performed to concentrate milk constituents before their spray-drying. During this step, the mineral fraction and especially calcium phosphate precipitates. The aim of this study was to evaluate the mineral behavior with a special attention paid on calcium and inorganic phosphate during vacuum evaporation of milk ultrafiltrate (UF) and milk microfiltrate (MF)). Water evaporation was performed with a pilot-scale falling-film evaporator with a configuration close to those used in industry. Samples were analyzed for levels of water evaporation. Different approaches were used like i. analyses of mineral contents and their precipitation; ii. theoretical calculation of salt formed and ion distribution. During evaporation, formation of trouble with presence of particles was determined. In the same time, increases of all components present were determined with a precipitation of calcium phosphate. With UF, deposits of calcium phosphate in the evaporator were deduced whereas with MF, interaction of calcium phosphate with whey proteins limited the calcium phosphate precipitation. The mineral precipitates were always negatively charged. Moreover and due to evaporation, the increase in the ionic strength significantly decreased the negative charge present at the surface of calcium phosphate precipitates.