Electrothermal effects of ohmic heating on biomaterials: Temperature monitoring, heating of solid-liquid mixtures, and pretreatment effects on drying rate and oil uptake

One of the main challenges in establishing a safety protocol for a continuous flow aseptic processing system is an accurate time-temperature heating data for both solid and liquid phases. The use of cholesteric liquid crystal sheets for temperature determinations in such a system is promising. However, this measurement technique is prone to errors due to variations in viewing and light source angles as well as the length of use of the liquid crystal sheet as demonstrated in our study.;Ohmic heating rates of a suspended solid particle and a medium have been studied experimentally under a range of conditions. The heating rate of the inclusion particle is significantly lower than that of the medium when the medium is electrically more conductive than the solid particle. Under this condition, the worst-case heating occurs under a well-mixed condition. On the contrary, when the suspended solid particle is electrically more conductive than the medium, the particle heats faster than the medium. Under this condition, the worst-case heating occurs under the well-mixed condition when the particle-to-heater cross section area ratio is 0.1, but it occurs under the static condition when the ratio is 0.2. A thermal crossover may be observed after a longer duration of heating, resulting in a more conservative heating under the mixed condition.;A modeling study to compare predictions of cold spot temperatures by the Laplace Equation No Convection (LENC) model and the Circuit Analogy Mixed Fluid (CAMF) model is also incorporated. Results suggest that the CAMF model is more conservative when the cold spot is within the solid particle, but the LENC model is generally conservative when the cold spot is within the medium.;The possibilities of applying ohmic heating as a pretreatment to increase the drying rate of grape berries and reduce oil absorption during frying and subsequent cooling of potato slices are also explored. We find that the drying rate of grapes is significantly increased by the ohmic pretreatment. Total oil uptake during frying and subsequent cooling of potato slices is decreased by an ohmic pretreatment without involving a liquid medium (direct sandwiching of slices between two electrodes).