Effect of heating by solid-state microwave technology at fixed frequencies or by frequency sweep loops on heating profiles in model food samples

One of the parameters that has the most influence in the uniformity of microwave heat processing is frequency. Unlike the traditional magnetron microwave system, it is possible to control and set up the frequency with the newly developed solid-state microwave system. The aim of this study was an investigation of the effect of fixed frequencies and frequency sweep loops (in the range of 2400–2500 MHz) on the uniformity of heat processing in circular gellan gel model samples containing Maillard reactive agents in a solid-state microwave system. Therefore, the purpose was to compare the solid-state system at fixed frequencies in which the megaton generator also works. While the magneton generator runs at random frequencies within a certain range, solid-state systems are capable of conducting heat processing at fixed frequencies. This novel characteristic will be evaluated through the implementation of different trials at various fixed frequencies. Additionally, the effect of changing frequencies is evaluated through frequency sweep loops, where the frequency of the solid-state system is changed in a pre-determined pattern. The results obtained from the time-temperature indicator of the Maillard reaction and the temperature indicator of infrared thermography showed that the heat processing of samples with the frequency sweep loops, even without turntable rotation, can be more uniform in comparison to those with fixed frequencies and turntable rotation. Moreover, the frequency sweep loops not only improved the uniformity of temperature distribution of the heated sample, but also increased the average temperature of processed samples and, thus, microwave heating absorption.