59D-33 |
Ultrasonic monitoring of unsteady state cooling of food products |
H. SIGFUSSON1, G. R. Ziegler2, and J. N. Coupland2. (1) Food and Agricultural Products Research & Technology Center, Oklahoma State University, FAPC RM 106, Stillwater, OK 74078-6055, (2) Department of Food Science, The Pennsylvania State University, 102 Borland Lab, University Park, PA 16802 The effectiveness of a chilling operation can be determined experimentally using thermocouples, or theoretically from heat transfer equations given geometry, starting conditions, and thermal properties of the material. Direct measurement using thermocouples is often impractical for process control, whereas the variable sample geometry and assumptions about material properties may limit theoretical evaluations. Thus, a method of non-invasive thermometry would be valuable. The objective was to use ultrasound to non-invasively monitor temperature changes during unsteady state cooling of foods. Food samples (gelatin, chicken, salmon, beef, and yogurt) were placed in a sample cell and immersed in a thermostated water bath to equilibrate at a uniform starting temperature (5-50.0°C). One face of the sample cell was then brought into contact with water at 0.5 ± 0.01°C while the other faces were insulated. The sample core temperature (±0.1°C) was monitored using a thermocouple and the time of flight (TOF) of an ultrasonic (2.25 MHz) pulse parallel to the direction of heat loss was measured simultaneously. The ultrasonic time of flight increased and the core temperature decreased with a decreasing rate during the cooling process, reaching a constant value when the change of temperature with time was zero. The cooling was modeled as one-sided unsteady-state heat transfer from an infinite slab. The local ultrasonic velocity could be calculated from theoretical temperature distribution and the total TOF was modeled by integrating this value over the whole width and dividing the results into sample thickness. The models of temperature and TOF agreed well with the measurements (r2 > 0.995). This ultrasonic method offers a non-invasive means to monitor product core temperature online during a food processing operation.
Session 59D, Food Chemistry: Proteins and Physicochemical Properties
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