## 3 Results and Discussion
### Thermal Inactivation of Model Foodborne Pathogens  
In the previous sections, it was demonstrated that the developed RF setup is capable of providing thermal treatments with the desired parameter values in TSB and BHI, both with and without bacterial cells. In a final step, the RF treatments were assessed for their bacterial inactivation potential.  
Figure 9 depicts the inactivation of _S. Typhimurium_ and _L. monocytogenes_ over the course of the RF treatments. For _S. Typhimurium_, inactivation started after 4-5 min, corresponding to a temperature of 47-51 \({}^{\circ}\)C. For _L. monocytogenes_, inactivation started after 5-6 min, corresponding to a temperature of 49-54 \({}^{\circ}\)C. These inactivation temperatures correspond to the minimal required temperatures for the inactivation of both microorganisms as reported in literature, i.e., approximately 50 \({}^{\circ}\)C for both _S. Typhimurium_ and _L. monocytogenes_[36; 37]. Bacterial counts were below the detection limit (DL) for all replicates after 8 min (T = 63 \(\pm\) 2 \({}^{\circ}\)C) and 10 min (T = 66 \(\pm\) 1 \({}^{\circ}\)C), for _S. Typhimurium_ and _L. monocytogenes_, respectively. For _S. Typhimurium_, bacterial counts were below the DL for samples taken after 8, 9, 10, 15, and 20 min, while for _L. monocytogenes_, bacterial counts were below the DL for samples taken after 10, 15, and 20 min. These treatment times of 8-10 min to achieve a 6 log reduction of bacteria in small samples of 3 mL are similar to those achieved in (isothermal) water baths [38]. Consequently, the developed RF setup is  
Figure 8: Power consumption profiles (average \(\pm\) SD) in TSB (**A**) and BHI (**B**) during RF treatments, both with and without bacterial cells. TSB and BHI were inoculated with _S. Typhimurium_ and _L. monocytogenes_, respectively.  
suitable for thermal inactivation experiments on both _S. Typhimurium_ and _L. monocytogenes_. If a slower or faster inactivation rate would be required for certain types of research, this can be achieved by controlling the input voltage of the setup. Different types of temperature profiles can also be achieved by using the voltage as a control parameter, e.g., heating up to a constant temperature at a high input voltage followed by a constant temperature phase at a lower input voltage. However, in this case, the effect of the voltage change on the frequency should be assessed to see whether further calibration is necessary. If researchers require this kind of control over the temperature profile, the voltage change could also be achieved with the power as an adjustable parameter. While the power-control of the setup is at this stage not possible in a direct way (i.e., without specific calculations), this could be implemented in order to acquire a more easily adjustable setup.  
In future research, it should also be taken into account that the resistance of bacteria to thermal treatments can be affected by the food model system [38]. Therefore, depending on their specific research interests, researchers could opt to wash and resuspend the cells in a fresh buffer medium when they want to discard food microstructural and/or compositional influences. Moreover, when studying the microbial inactivation in detail, it will be beneficial to obtain information on potential temperature heterogeneities in the  
Figure 9: Cell densities (average \(\pm\) SD) at different time points during the RF inactivation of _S. Typhimurium_ in TSB (**A**) and _L. monocytogenes_ in BHI (**B**). Bacterial counts were below the detection limit (DL) after a treatment time specific for each microorganism.  
sample. Even though the setup has been designed to minimise temperature heterogeneities compared to commercial systems, small temperature differences could still be worth considering when interpreting microbial inactivation data.