1. Introduction
Conventional thermal processes for solid and semi-solid foods
in large containers, such as size 10 cans (159 mm diameter,
178 mm height) for food services or 6 lb capacity (295 mm
length, 254 mm width and 42 mm depth) trays for US military
group meal rations, often lead to severe overheating at the
periphery of the foods by the time the package interior reaches
the desired sterility for heat resistant food pathogens. Dielectric
heating by microwave or radio-frequency (RF) energy shortens
thermal processes because heat is generated by direct interaction
between electromagnetic energy and the foods within food packages.
The free-space wavelength in the RF range (e.g., 13.56,
27.12 and 40.68 MHz) is 20–360 times longer than that of commonly
used microwave frequencies (e.g., 915 and 2450 MHz),
allowing RF energy to penetrate foods more deeply than microwave
energy. Thermal processing with RF heating is, therefore,
suitable for large food trays (Wang et al., 2003c). Indeed, our
previous inoculated pack studies (Luechapattanaporn et al.,
2004, 2005) demonstrated that RF energy has adequate penetrations
to inactivate heat resistant bacteria spores in food prepackaged
in 6-lb capacity polymeric trays. We have also demonstrated
with a pilot-scale RF sterilization unit that the total time
for RF processing of foods in 6-lb capacity trays was reduced to