5. Conclusions
The computer simulation revealed that different dielectric
properties of components in heterogeneous foods caused large
variations in electric field and dissipated energy in different food
components. Results from pilot plant testing at 27.12 MHz and
computer simulation indicated that the vastly different temperature
dependent loss factors among different food components at
27.12 MHz did not cause major nonuniform heating inside heterogeneous
foods, such as lasagna that contains beef meatballs, mozzarella
cheese, noodles, and sauce, when different food
components are evenly dispersed in close proximity. Reduced electric
field intensity in sauce with much higher loss factor compared
to the other food components prevented it from being over heated.
The distribution, shape, size, and especially heat transfer ability of
the food components should have important influences on the
heating uniformity.
The results from this study show that RF heating has a potential
to produce safe, high quality pre-packaged heterogeneous food. RF
heating has advantages over retort heating when processing semisolid
food because of short heat-up times and relatively uniform
temperature distribution, resulting in less degraded food products.
Proper distribution and suitable amounts and sizes of each component,
though with vastly different dielectric properties, can provide
relatively uniform RF heating.
In spite of the encouraging results, we believe it remains a major
engineering challenge to scale an RF sterilization system as described
in this study for industrial applications, due to the
complicated design requirements and need for precise control of
circulation water temperature to reduce RF fringe effects on heating
uniformity in food. Absorption of RF energy by the circulation
water also reduces the effective use of RF energy.