15C-12 |
Ultrasonic monitoring of the solid/liquid boundary in lipids during crystallization |
H. SIGFUSSON1, G. R. ZIEGLER2, and J. N. Coupland2. (1) Oklahoma Food & Agricultural Products Research & Technology Center, Oklahoma State Univ., Rm. 106, Stillwater, OK 74078, (2) Dept. of Food Science, Pennsylvania State Univ., 102 Borland Lab., University Park, PA 16802 Chocolate enrobing processes depend on rapid and controlled liquid/solid transition to lock the coating in place before it drains. There are few methods available to measure the rate of movement of the solid front, which would be a useful parameter to model this process. The objectives were to non-invasively monitor the movement of the solid/liquid interface and solid fat content in simple and complex lipid mixtures during unsteady state cooling using ultrasound. Lipid samples (hexadecane, confectionary coating fat (CCF), and chocolate) were placed in a sample cell and immersed in a thermostated water bath to bring the sample to a uniform starting temperature (50.0°C) above its melting point. Once equilibrated, one thin walled aluminum face of the sample cell was brought into contact with water at 0.0 ± 0.01°C while the other sample walls were insulated. The sample core temperature was monitored using a thermocouple. The time of flight (TOF) of an ultrasonic (2.25 MHz) pulse parallel to the direction of heat loss was measured simultaneously. Echoes were recorded from sample boundaries and the moving solid lipid front. The temperature and total ultrasonic time of flight (TOFtotal) through the sample decreased at a decreasing rate during the cooling process. The rate of change of the echo time from the solid/liquid interface was equivalent to the speed of solid front movement and was initially 4.4 and 8.8 mm/s for hexadecane and CCF respectively. No solid/liquid interface could be observed in chocolate. The TOFtotal was used to calculate the solid fat content. This ultrasonic method offers a non-invasive means to monitor lipid liquid/solid ratio during processing. It is also capable of “seeing” the location of a moving boundary in optically opaque lipid samples.
Session 15C, Food Chemistry: Food composition and analysis
|