Models for ohmic heating of solid-liquid mixtures under worst-case heating scenarios

Sterilization of solid-liquid mixtures by ohmic heating requires the assurance that all parts of the food or biomaterial in question is treated adequately to ensure inactivation of pathogenic sporeforniers. Previous work has identified worst-case scenarios as being associated with a single solid piece (inclusion particle) of substantially different electrical conductivity than its surroundings. Two potentially hazardous situations were modeled, both involving an inclusion particle, but one involving a static medium surrounding the solid; and the other involving a mixed fluid, with a circuit theory analysis for the electric field. Results indicate that the mixed fluid model provides a more conservative prediction of mixture cold-spot temperatures than the static model when the cold-spot occurs within the particle; typically occurring when the medium is more conductive than the solid. However, the static fluid model provides more conservative prediction of the mixture cold-spot temperatures when the cold-spot is within the fluid; typically when the solid is more conductive than the medium. Our results underline the need to evaluate both scenarios in evaluating the potential for an underprocessed region. (c) 2007 Elsevier Ltd. All rights reserved.