Ultrasonic velocity measurements in frozen model food solutions

The speed of sound was measured in solutions of sucrose (0-70 wt/vol%), glycerol (0-30 wt/vol%) and orange juice (0-40 solids wt/vol%) as a function of temperature (10 °C to -13 °C). The velocity (c) in the unfrozen solutions, including the supercooled samples, could be modeled as a simple linear function of temperature (T, °C) and composition (x, wt/vol%): c = c_w + k_xx + k_TT where c_w is the speed of sound in water at 0 °C, and k_x and k_T are solute-dependant constants. There was a large increase in ultrasonic velocity corresponding to freezing in these samples (e.g., an unfrozen 10% sucrose solution has a speed of sound of 1416 m s^-1 at -5 °C while a similar frozen solution has a velocity of 1983 m s^-1). The ice content was estimated from phase diagrams of similar samples and was a linear function of the change in ultrasonic velocity upon freezing for samples <8 °C. Some details of the effects of ice microstructure and possible theoretical approaches to its effects on ultrasonic properties are also discussed.