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

Abstract

The effect of Listeria monocytogenes, Salmonella Typhimurium, and Saccharomyces cerevisiae on RF heating was studied in sterilized Milli-Q water and saline solution during treatments at 27.0 ± 0.6 MHz and 3.0 ± 0.02 MHz for 30 min. The presence of microorganisms caused a significant increase in temperature (maximum to 54.9 °C), with no significant decrease in cell numbers being observed for any conditions. For both media and frequencies, heating rates followed the order S. Typhimurium ≤ L. monocytogenes ≤ S. cerevisiae, except for heating at 3.0 ± 0.02 MHz in saline solution, where heating rates for S. cerevisiae and S. Typhimurium were equal. Generally, heating rates for microorganisms were significantly higher at 27.0 ± 0.6 MHz than at 3.0 ± 0.02 MHz, except for the S. cerevisiae case. Observed phenomena were probably caused by differences in the cell lipid and peptidoglycan content, with interaction effects with salt being present. This study was the first to investigate the influence of the presence of microorganisms on heating behavior of simple media. On the long term, more research on this topic could lead to finding specific RF frequencies more suitable for the heating of specific media and products for various applications.

Figure 1

Average temperature profiles and standard deviation (every 5 min) for L. monocytogenes, S. Typhimurium, and S. cerevisiae at 27.0 ± 0.6 MHz. Ten independent experiments were conducted for each condition.

Figure 2

Average temperature profiles and standard deviation (every 5 min) for L. monocytogenes, S. Typhimurium, and S. cerevisiae at 3.0 ± 0.02 MHz. Ten independent experiments were conducted for each condition.

Figure 3

Interaction effect on RF heating of microorganisms and NaCl solution.