Analysis of temperature-dependent bacterial dielectric properties for effective PEF pasteurization

Pre-heating enhances the bactericidal efficacy of pulsed electric field (PEF) treatment. This study provides a solid foundation for optimizing the temperature history of pre-heating for the PEF pasteurization. The capacitance and conductance of the suspensions of Enterobacter hormaechei were analyzed as the temperature increased and decreased. In addition, the membrane permeability after heating and cooling was examined to verify the impedance analysis. Furthermore, the viability of bacteria after the application of PEF (20 kV/cm, 2 μs, 5 times) after heating and cooling was investigated to discuss its relevance to the membrane properties obtained from the impedance analysis. The results indicated that the capacitance of the bacterial suspension increased as the temperature increased from 25 to 45 °C; at ≥ 47 °C, the capacitance decreased and the conductance increased simultaneously. At the maximum temperature of ≤ 45 °C, the change in the bacterial membrane property was reversible, whereas, at ≥ 50 °C, the bacterial membrane was irreversibly denatured. For PEF treatment, the higher the treatment temperature, the stronger the bactericidal effect. Cooling after pre-heating can affect the bactericidal effect, with a significant decrease at ≤ 45 C and only a slight decrease at > 50 °C, where irreversible denaturation occurs. • Capacitance and conductance of bacterial suspension at increasing and decreasing temperatures were measured. • Bacterial membrane properties and permeability change dynamically with temperature change. • The change in bacterial membrane properties is reversible at T m < 45°C, and irreversible at T m > 50 °C. • The higher the temperature at which PEF is applied, the lower the number of viable bacteria. • At T m > 50 °C, PEF bactericidal effect is maintained even after cooling because of the irreversible change of the membrane.