Ohmic heating of foods: Studies on microbicidal effect of electricity, electrical conductivity of foods, and heat transfer in liquid-particle mixtures

A device was developed for conventional or ohmic heating of biomaterials, and modified for electrical conductivity measurement of foods during heating.;Death kinetics of yeast cells were compared under conventional and ohmic heating conditions by subjecting cell suspensions in a phosphate buffer solution to identical time-temperature histories. No significant difference was found in the death rates during conventional and ohmic heating. However, electrical pretreatment studies on Escherichia coli indicated increased inactivation under certain combinations of sublethal electrical pretreatment and conventional heating.;Electrical conductivities of various juices, vegetables, and meats were determined during conventional and ohmic heating. Electrical conductivity of juices increased with temperature and decreased with solids content, and that of solid foods increased linearly with temperature at 60 V/cm. For solid foods, the linearity of conductivity curves during ohmic heating gradually changed when decreasing applied voltage, ending in a non-linear curve for conventional heating. Soaking vegetable tissue in water reduced conductivity, whereas salt solutions increased tissue conductivity as manner dependent on the salt concentration.;A mathematical model based on probability distribution and electrical circuit theory was developed to determine the effective electrical conductivity of liquid-particle mixtures. The results of this and previous models were compared with the experimental values for mixtures of potato cubes and sodium phosphate solutions. Differences between experimental and model results (except for the series model) were within the same range. Conductivities predicted by the probability model were in good agreement below 60;Two heat transfer models, based on different electrical circuit assumptions, were developed for ohmic heating of liquid-particle mixtures in a static heater. Simulated temperatures of liquid and particles were compared with the experimental temperatures obtained for potato cubes and sodium phosphate solutions. The model with a parallel liquid element for the length of the heater predicted reasonable temperatures using low convective heat transfer coefficients. The heating rates of liquid and particles depended on their electrical conductivities, and size and volume fraction of particles.