Mathematical modeling of ohmic heating for inactivation of acid-adapted foodborne pathogens in tomato juice

The objective of the present study was to predict the inactivation trends of acid-adapted foodborne pathogens in tomato juice by ohmic heating through a numerical analysis method. The mathematical model based on finite element method (FEM) was used to simulate the multiphysics phenomena including electric heating, heat transfer, fluid dynamics, and pathogen inactivation. A cold spot was observed in the corner part of the ohmic heating chamber, where some pathogens survived even though all pathogens were inactivated elsewhere. Challenges of this study were how to reflect the increased resistance of pathogen by acid-adaptation. After simulation, we verified that inactivation level of acid-adapted foodborne pathogens by 25 Vrms/cm ohmic heating (1 kHz), predicted with the developed mathematical model, had no significant differences with experimental results (p > 0.05). Therefore, the mathematical approaches described in the present study will help juice processors determine the processing conditions necessary to ensure microbial safety at the cold point of a rectangular type batch ohmic heater.

Laminar forced convection in a cylindrical collinear ohmic sterilizer

The present work deals with a thermo-fluid analysis of a collinear cylindrical ohmic heater in laminar flow. The geometry of interest is a circular electrically insulated glass pipe with two electrodes at the pipe ends. For this application, since the electrical conductivity of a liquid food depends strongly on the temperature, the thermal analysis of an ohmic heater requires the simultaneous solution of the electric and thermal fields. In the present work the analysis involves decoupling the previous fields by means of an iterative procedure. The thermal field has been calculated using an analytical solution, which leads to fast calculations for the temperature distribution in the heater. Some considerations of practical interest for the design are also given.