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Streszczenie:
The purpose of the paper is to address, using ultrasonic methods, the impact of temperature and pressure on the physicochemical properties of liquids on the example of diacylglycerol (DAG) oil. The paper presents measurements of sound velocity, density and volume of DAG oil sample in the pressure range from atmospheric pressure up to 0.6 GPa and at temperatures ranging from 20 to 50°C.

Sound speed measurements were performed in an ultrasonic setup with a DAG oil sample located in the high-pressure chamber. An ultrasonic method that uses cross-correlation method to determine the time-of-flight of the ultrasonic pulses through the liquid was employed to measure the sound velocity in DAG oil. This method is fast and reliable tool for measuring sound velocity. The DAG oil density at high pressure was determined from the monitoring of sample volume change. The adiabatic compressibility and isothermal compressibility have been calculated on the basis of experimental data. Discontinuities in isotherms of the sound speed versus pressure point to the existence of phase transitions in DAG oil. The ultrasonic method presented in this study can be applied to investigate the physicochemical parameters of other liquids not only edible oils.

Słowa kluczowe:
Ultrasonic methods, Sound velocity, Phase transitions, High pressure food processing, Physicochemical parameters

Streszczenie:
The influence of high pressure on viscosity and compressibility of diacylglycerol (DAG) oil has been presented in this paper. The investigated DAG oil was composed of 82% of DAGs and 18% TAGs (triacylglycerols). The dynamic viscosity of DAG was investigated as a function of the pressure up to 400 MPa. The viscosity was measured by means of the surface acoustic wave method, where the acoustic waveguides were used as sensing elements. As the pressure was rising, the larger ultrasonic wave attenuation was observed, whereas amplitude decreased with the liquid viscosity augmentation. Measured changes of physical properties were most significant in the pressure range near the phase transition. Deeper understanding of DAG viscosity and compressibility changes versus pressure could shed more light on thermodynamic properties of edible oils.

Słowa kluczowe:
DAG viscosity, compressibility, phase transitions, transmitted and scattered light

Streszczenie:
In this article, the influence of high pressure on sound velocity at 293 K has been presented. The investigated diacylglycerol oil (DAG – [D82T18]AG) was composed of 82% DAGs and 18% triacylglycerols. The variation of sound velocity with hydrostatic pressure for DAG was evaluated up to 400 MPa. The phase transformation in DAG has been observed as a discontinuity of the dependence of sound velocity on pressure. The sound velocity during the phase transition has shown distinct increment. Also the volume changes have been measured. It has shown the rapid drop of the volume at the phase transformation pressure due to the possible crystallization of DAG oil.

Słowa kluczowe:
high pressure, velocity, DAG

Streszczenie:
In this paper, phase transitions in diacylglycerol (DAG) oil are investigated by using an ultrasonic method for measuring viscosity. Viscosity of diacylglycerol (DAG) oil is measured over a wide range of hydrostatic pressures up to 500 MPa, and at temperatures ranging from 10 to 40 °C. The observed discontinuities in the viscosity versus pressure curves (isotherms) indicate phase transitions. An original ultrasonic method that uses the surface acoustic Bleustein–Gulyaev (B–G) wave was employed to measure the viscosity of DAG oil at high pressure range. This method allows for fast and reliable measurement of DAG oil viscosity along various isotherms. Moreover, the kinetics of the observed phase transformations at various temperatures was analyzed. The results of the study are a novelty, and can be helpful in evaluating the physicochemical properties of edible oils.

Słowa kluczowe:
Edible oils, Ultrasonic methods, Diacylglycerols, Viscosity, Phase transitions, High pressure

Streszczenie:
Phase transitions in diacylglycerol (DAG) oil were investigated by using an ultrasonic method for measuring viscosity. Viscosity of DAG oil was measured over a wide range of hydrostatic pressures up to 500 MPa, and at temperatures ranging from 10 to 40 °C. The observed discontinuities in the viscosity versus pressure curves (isotherms) indicate phase transitions. An original ultrasonic method that uses the surface acoustic Bleustein-Gulyaev (B-G) wave was employed to measure the viscosity of DAG oil at high pressure range. This method allowed for fast and reliable measurement of DAG oil viscosity along various isotherms. Moreover, the kinetics of the observed phase transformations at various temperatures was analyzed.

Słowa kluczowe:
Viscosity, Temperature measurement, Ultrasonic variables measurement, Acoustics, Pressure measurement, Acoustic measurements, Liquids