Orange juice pvT-properties for high pressure processing and modeling purposes: Importance of soluble solids concentration

Both freeze-concentration and high pressure treatments are promising technologies that can be combined in order to improve juice quality and increase shelf life. Mathematical modeling is a useful tool to design, to develop and to optimize these processes but it faces a lack of data on physical properties of foods at high pressure. For that reason, the volumetric properties of orange juice and concentrates (12 to 40 degrees Brix) were determined at temperatures between -20 degrees C and +40 degrees C and pressures up to 350 MPa. A variable volume piezometer was used for that purpose. The coefficients of an equation of state initially developed for water were fitted to allow for calculating the specific volume as a function of pressure and temperature. The isothermal compressibility and the thermal expansion coefficients calculated from the resulting equation of state show similar behaviors as those of water with some subtle differences. Temperatures of specific volume and compressibility coefficients minima are shifted toward lower values than those of water as solutes concentration increases. Volumetric properties progressively tend to behave as those of a solid. Any use of water properties to approximate orange juice concentrate properties behavior under pressure gives rise to significant uncertainties when calculating adiabatic heat. Studies about the sensitivity of models to each property and to their respective uncertainty would help in pointing out experimental needs and accuracy requirements for the determination of food thermophysical properties at high pressure. (C) 2011 Elsevier Ltd. All rights reserved.