Ultrasonic velocity measurements in frozen model food solutions

Abstract

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 x x + k T T 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.