Computer simulation of ohmic heating of a heterogeneous model food with an irregular geometry

Introduction:

Ohmic heating (OH) of heterogeneous foods is challenging as geometric and electrical variations cause a non-uniform temperature distribution. Additionally, biological variability makes it difficult to isolate these factors using real foods. Thus, developing model foods and mathematical simulations is essential to optimize the OH process. This study developed a non-homogeneous konjac glucomannan (KGM) model food mimicking a salmon fillet's irregular geometry and varying electrical properties, while a 3D OH simulation model was constructed and validated.

Methods:

KGM gels were prepared and molded into salmon fillet shapes. To simulate spatial variations in muscle properties, the model food incorporated multiple sections with varying NaCl concentrations (e.g., 0, 0.2, 0.35, 0.5 wt%). Samples were placed in a polyethylene mold with 0.35 wt% NaCl solution and heated from 10°C to 90°C (20 kHz, 30 V) using a Joule heating machine (FJB-5.5, Japan). Temperatures were monitored at three locations using fiber-optic sensors. A 3D model coupling electric current and heat transfer was constructed in COMSOL Multiphysics 6.4 using the finite element method.

Results and Discussion:

Simulated temperature distributions agreed well with experimental measurements, confirming model validity. Heating was relatively uniform overall; however, the central monitoring location exhibited slightly lower temperatures than the lateral positions, attributed to sample thickness variation. Current density analysis revealed an approximately twofold difference between peripheral and central regions, caused by the fillet-shaped geometry and preferential current pathways through the surrounding salt solution along both sides of the sample.

Conclusions:

The KGM-based model food system enabled flexible property modification and accurate replication of complex, non-uniform food geometries. The 3D finite element simulation successfully predicted both temperature and current density distributions during the OH process, providing a validated framework to guide future optimization of OH processing for heterogeneous foods with irregular geometries and electrical properties to improve heating uniformity.