Nondestructive monitoring of sucrose diffusion in oil-in-water emulsions by ultrasonic velocity profiling

The diffusion of sucrose through an optically opaque oil-in-water emulsion was monitored nondestructively by measuring the ultrasonic velocity as a fu nction of height. Initially, a corn oil-in-water emulsion (0, 5, 10, 15, or 20 wt% oil) stabilized by Tween 20 (1 wt%) and xanthan (1 wt%) was placed in a measurement cell at 30 degrees C. A 20 wt% sucrose solution containing the same concentration of Tween, 20 and xanthan as the aqueous phase in th e emulsion was placed on top of the emulsion. The ultrasonic velocity of th is two-layer system was measured as a function of sample height and time an d then converted into sucrose and oil concentration- distance profiles usin g empirical calibration curves. The translational diffusion coefficient of the sucrose in the upper and lower layers was determined by fitting the exp erimental data to a Fickian diffusion model. The measured diffusion coeffic ients of the sucrose molecules decreased as the droplet concentration in th e emulsion increased, indicating retardation of the sugar molecule movement . Ultrasonic profiling was also used to monitor the compression of the emul sion due to movement of water molecules into the upper layer. (C) 1999 Acad emic Press.