Determination, analysis and prediction of the volumetric behavior of milk at high pressure

High pressure preservation technologies are consolidating in the food industry as an interesting alternative to traditional thermal processes. Process modeling contributes to its progress and requires the input of food properties like density for calculations. The dependency on pressure of these properties is indispensable but it is rarely available in the literature. The sector of dairy products is an important target for the development of novel foods by high pressure treatments (both high hydrostatic pressure processing and ultra-high pressure homogenization). Thus, the main objective of this research was to characterize the volumetric properties of raw whole milk and skim milk. A variable-volume piezometer with a solid-piston volumeter was employed for this purpose. Density, specific volume, isothermal compressibility and thermal expansion coefficient were determined between 0 and 60°C under pressures up to 350MPa; at atmospheric pressure, measurements cover temperatures up to 90°C. Results show that milk solutes and fats, although present in low quantities in milk compared to water, have an influence which is worthy of consideration on milk volumetric properties. Irregularities appear from 200MPa in the dependencies on temperature of the studied milk properties. From a composition-based model, it is highlighted that milk solutes' specific volume behavior is inverted around 55°C and that milk fats' compressibility goes through a maximum around 30°C. The composition-based model is further developped for the calculation of milk properties as a function of pressure at different temperatures; prediction errors are below 2%. Useful data and equations for high pressure processing simulation are provided together with an original view on the combined effects of pressure and temperature on milk solutes and fats.