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Abstract
We measured the velocity of sound in olive oil under pressure with the Brillouin light scattering technique. Using the values for the density and the thermal conductivity that have only recently been reported, we calculated the adiabatic compressibility and the isobaric specific heat up to 356 MPa and the thermal diffusivity up to 200 MPa. The specific heat displays a maximum at 124 MPa, suggesting a possible phase transition around this pressure. Apart from the theoretical and practical importance of these results for the food industry and beyond, this work shows that Brillouin light scattering and macroscopic methods are complementary and can be employed to measure thermophysical parameters of food liquids under pressure.
Keywords Olive oil * Pressure * Brillouin light scattering * Specific heat * Thermal diffusivity * Compressibility
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Introduction
Due to its advantages with respect to the traditional thermal approach, high-pressure technology has become an attractive option for food processing [I]. Computer simulations are, like in many other fields, useful complementary investigative tools but they require physical parameters for food under pressure, information that is still scarce. For example, until recently, the density of some natural oils was known only up to 145 MPa [2], while the isobaric specific heat, thermal diffusivity, and thermal conductivity only up to 49 MPa [3]. These values are too low when compared to the pressures used in the food industry and offer only a limited insight into the properties of these materials, as demonstrated by later studies in which higher pressures were reached.
During the last 2 years, the density [4, 5] and the thermal conductivity [4] of some edible oils have been reported at several temperatures and pressures exceeding 400 MPa. This breakthrough allows one to derive the dependence of other physical parameters, such as the isothermal compressibility and the thermal expansion coefficient, on temperature and pressure [5]. However, the isobaric specific heat at higher pressures - a necessary parameter for feeding the models used to predict die heat transfer under pressure and microorganism inactivation [1, 5] - remains elusive.
Here, we apply the Brillouin light scattering (BLS) technique to measure the velocity of sound in olive oil at ambient temperature and high pressures and, using the values...