Electromagnetics, heat transfer, and thermokinetics in microwave sterilization



Sterilization of solid foods using microwave power was studied using numerical modeling and specialized experimental verification. Maxwell's equations and the heat conduction equation were coupled using two separate finite-element programs and specially written modules to couple the programs. Spatial distributions of thermal-time, representing sterilization, were calculated from time-temperature history and first-order kinetics. Experimentally, concentrations of marker compounds formed during heating were measured and taken as indices of thermal-time. Experimental data on marker formation combined with numerical calculations provide an accurate and comprehensive picture of the sterilization process and represent a major step in establishing the efficacy of microwave sterilization processing. Unlike conventional sterilization, heating patterns can change qualitatively with geometry (shape and size) and properties (composition) of the food material, but optimal heating is possible by choosing suitable combinations of these factors. Combined with marker yield measurements, the numerical model can give comprehensive descriptions of the spatial time-temperature history, and thus can be used to verify the sterilization process.