Mathematical modeling and microbiological verification of ohmic heating of a solid–liquid mixture in a continuous flow ohmic heater system with electric field perpendicular to flow

• A mathematical model is developed for solid–liquid mixtures in an ohmic heater with electric field perpendicular to the flow.
• The model is validated by thermal and microbiological verification.
• There is a good agreement between model predictions and experimental findings.
• The model is capable of ensuring sterility in a continuous ohmic sterilization process for a solid–liquid mixture.

To ensure sterility of a solid–liquid mixture processed in continuous-flow ohmic systems, the slowest-heating solid particle needs to receive sufficient heat treatment at the outlet of the holding section. We describe herein, the development of a mathematical model for solid–liquid mixtures in a commercial ohmic heater with electric field oriented perpendicular to the flow. The fastest moving particle velocity was identified using over 299 particles and a radio-frequency identification technique, and used as an input to the model for the worst-case heating scenario. Thermal verification was conducted by comparing predicted and measured fluid temperatures at heater and hold tube outlets; the model showed good agreement between calculated and experimental fluid temperatures (P > 0.05) with a maximum error of 0.4 °C. The model predicted a hold tube length of 15.85 m at 134.0 °C process temperature to achieve a target lethal effect at the cold spot of the slowest-heating particle. Using this length of hold tube, microbiological tests were conducted using at least 299 chicken/alginate particles inoculated with Clostridium sporogenes spores per run. These tests showed the absence of viable microorganisms at the target treatment and positive growth when temperatures were below target, thereby verifying model predictions.