This research was to investigate the feasibility for developing a short-time sterilization protocol for a
highly inhomogeneous food prepackaged in polymeric trays using 915 MHz microwave (MW) energy.
A 915-MHz, single-mode, 10-kW pilot-scaleMWsystem developed at Washing State University was used
for this study. The inhomogeneous food consisted of sliced beef and gravy packaged in 7-oz polymeric
trays. Specially formulated whey protein gel, matching the beef product in their dielectric properties,
was chosen as a model food to emulate the real food for determination of heating patterns and cold spots
inside food trays. The heating patterns and cold spots were detected using a chemical-marker-assisted
computer vision method. Processing schedules to achieve desired levels of F0 for 7-oz trays of beef in
gravy were established based on temperature histories measured at the identified cold spot location.
The developed processing schedules were validated by inoculated pack studies using Clostridium sporogenes
PA 3679 spores. The results of this study indicate that the 915-MHz single-mode MW sterilization
technology is effective for processing of the inhomogeneous food. The procedure established could be
used for developing MW sterilization processes for other packaged inhomogeneous foods, such as
chicken meat in gravy in trays and salmon in sauce in pouches. The processing data collected could be
helpful for industrial scale-up of the MW system.