a b s t r a c t
This research studied the influence of frequency variation on heating patterns within prepackaged foods
in a 915 MHz single-mode microwave assisted sterilization (MATS) system consisting of four microwave
heating cavities. The frequencies of the four generators powering the MATS system at Washington
State University were measured at different power levels over one year. The effect of frequency shifts
in the generators on heating patterns within a model food (whey protein gel, WPG) was studied through
computer simulation. The simulated heating patterns were experimentally validated using a chemical
marker. Our measurement results showed that a 0.5 kW increase in the microwave power caused the
operating frequencies of the generators to increase by 0.25–0.75 MHz. The simulation results suggested
that the heating pattern of WPG processed by the MATS system was not affected by the varying
frequencies of generators within the operating frequency bandwidth (900–920 MHz). In addition, the
simulation results revealed that using deionized water as the circulation medium in the MATS system
resulted in a 23–37% increase in the temperature of WPG as compared with that when using normal
tap water, but did not alter the heating pattern