Hysteresis of ultrasound velocity in pork lard and water during a thermal cycle

• Occurrence of hysteresis of ultrasonic wave velocity in lard in the temperature range of 10 °C–40 °C has been confirmed.
• Hysteresis of ultrasonic wave velocity in the mains water was not significant.
• Velocity hysteresis in fat should be taken into consideration at planning food industry processes.

Today, quick measurement methods, including methods of determination of food composition, are becoming increasingly important. The answer to the growing need is a non-destructive and very quick ultrasonic method. To determine the composition of a material with this method, it is necessary to determine the velocity of ultrasonic wave propagation in individual ingredients, which may vary depending on whether the material is cooled down or heated up, i.e. its hysteresis. The aim of this study was to determine if hysteresis occurs in ground meat during a thermal cycle.The key ingredients of ground meat are proteins, fat and water. Since there is currently no method available to obtain protein in a form allowing acoustic measurements thereof, samples of pork fat and process water were analyzed. The thermal cycle involved cooling down and heating the samples in a temperature range of 10–40 °C. The measurements were performed by the transition method, using two heads of ultrasonic l-wave with a frequency of 2 MHz. The occurrence of hysteresis during the thermal cycle within the analyzed temperature range was confirmed in lard samples, while in the case of water, hysteresis proved to be negligibly low. To minimize the uncertainty of the quantification of the composition of ground meat by the ultrasonic method the industrial applications must provide for the hysteresis of ultrasound velocity in fat.