29D-4 |
A simulated system for process evaluation in ohmic heating of two-phase food systems |
J. S. B. WU, Institute of Food Science and Technology, National Taiwan University, P. O. Box 23-14, Taipei, 106, Taiwan Ohmic heating is an effective heating method for fluid containing particles. However, it is difficult to determine the time-temperature history inside these particles, as they are in constant move in the entire process. To construct a simulated system with an accessible cold point may be a feasible approach. Our objective was to establish a simulated system for evaluating ohmic heating processes in some food systems containing fluid and particles. The heat transfer at the interface between fluid and particles, in different shapes, orientations and volume ratios, in an ohmic heater was investigated by theoretical deduction, and then by laboratory experiments. The food system used in the experiments was potato particles in 0.25% citric acid solution. Our results show that the heating rate of a particle decreases with an increase in the depth of fluid in series in the electric conduction path if the particle has a higher electric conductance than the fluid and the solid/liquid volume ratio in the system remains unchanged. The center of a cuboid characterized with a volume equivalent to the summation of the volumes and a height equivalent to the least packed height of all the particles along the full length in the ohmic heater heats up slower than any point in the component particles. These results suggest the construction of a model system containing such a cuboid in establishing ohmic processes for foods composed of fluid and particles provided the solid phase has a higher electric conductance than the liquid phase. The center of that cuboid can be taken as the cold point in the process evaluation to assure achieving a higher sterilization value everywhere in the real system.
Session 29D, Food Engineering: Thermal processes
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