Mathematical Modeling and Microbiological Verification of Ohmic Heating of a Multicomponent Mixture of Particles in a Continuous Flow Ohmic Heater System with Electric Field Parallel to Flow



To accomplish continuous flow ohmic heating of a low-acid food product, sufficient heat treatment needs to be delivered to the slowest-heating particle at the outlet of the holding section. This research was aimed at developing mathematical models for sterilization of a multicomponent food in a pilot-scale ohmic heater with electric-field-oriented parallel to the flow and validating microbial inactivation by inoculated particle methods. The model involved 2 sets of simulations, one for determination of fluid temperatures, and a second for evaluating the worst-case scenario. A residence time distribution study was conducted using radio frequency identification methodology to determine the residence time of the fastest-moving particle from a sample of at least 300 particles. Thermal verification of the mathematical model showed good agreement between calculated and experimental fluid temperatures (P > 0.05) at heater and holding tube exits, with a maximum error of 0.6 °C. To achieve a specified target lethal effect at the cold spot of the slowest-heating particle, the length of holding tube required was predicted to be 22 m for a 139.6 °C process temperature with volumetric flow rate of 1.0 × 10−4 m3/s and 0.05 m in diameter. To verify the model, a microbiological validation test was conducted using at least 299 chicken-alginate particles inoculated with Clostridium sporogenes spores per run. The inoculated pack study indicated the absence of viable microorganisms at the target treatment and its presence for a subtarget treatment, thereby verifying model predictions.

Practical Application

The manuscript describes the detailed development and verification protocol of a mathematical model of a sterilization process for a liquid food containing 5 different types of solid food particles, within a continuous ohmic heater with electric field parallel to product flow. Our findings demonstrate that the model is capable of designing an ohmic thermal process for multicomponent solid–liquid food mixtures, and represents the development of a theoretical and experimental framework for companies interested in filing ohmic sterilization processes with the Food and Drug Administration.