Design of a Low-Power Radio Frequency Unit and Its Application for Bacterial Inactivation under Laboratory Conditions

Abstract

A lab-scale low-power free-running radio frequency (RF) oscillator operating at a frequency of 27.12 ± 0.50 MHz was developed to be suitable for fundamental microbiological research topics. Calibration and validation were conducted for two common foodborne pathogens in relevant microbiological growth media, i.e., Salmonella Typhimurium and Listeria monocytogenes in Tryptic Soy Broth and Brain–Heart Infusion broth, respectively. The evolution of temperature, frequency, and power consumption was monitored during treatments, both with and without bacterial cells. The setup operated within the predefined frequency range, reaching temperatures of 71–76 °C after 15 min. The average power consumption ranged between 12 and 14 W. The presence of bacteria did not significantly influence the operational parameters. The inactivation potential of the RF setup was validated, demonstrating the absence of viable cells after 8 and 10 min of treatment, for S. Typhimurium and L. monocytogenes, respectively. In future studies, the setup can be used to conduct fundamental microbiological studies on RF inactivation. The setup can provide added value to the scientific field, since (i) no consensus has been reached on the inactivation mechanisms of RF inactivation of pathogens in foods and (ii) most commercial RF setups are unsuitable to adopt for fundamental studies.

Influence of microbial cell morphology and composition on radio frequency heating of simple media at different frequencies

“…RF experiments were conducted using two small-scale laboratory RF setups, built according to the flyback topology design using an air-core transformer (Tesla coil), as described for an 27.12 MHz setup in Kozak et al . 33 . Both RF set-ups were free-running oscillators operated at 27.0 ± 0.6 MHz and 3.0 ± 0.02 MHz, respectively.…”

“…The other parts of both RF setups (e.g., power supply, cooling fan) were constructed as described in detail in Kozak et al . 33 . All experiments were conducted using 3 mL samples in the mentioned small glass vials, which were equipped with a polypropylene screw cap lid with a glass capillary tube inserted through the middle of the lid (i.e., to enable temperature measurements).…”