ID: 2205

  • Title:
    Study of Bacterial Membrane Recovery after PEF Exposure Using Frequency Domain Reflectometry


    Pulsed electric field (PEF) has attracted attention as one of the promising non-thermal sterilization methods since it can effectively permeabilize bacterial membranes without significant Joule heating. However, electro-permeabilized membrane is considered to recover in a certain condition within minutes, resulting in weakening the bactericidal effect of PEF. Therefore, PEF is often combined with a subsequent moderate thermal energy to enhance the bactericidal effect. There are few studies that report the recover process in minutes range after the PEF treatment. However, the recovery process is anticipated to progress in seconds or less from the view point of the thermal motion of lipids in membrane. Purpose of this study is to investigate the time range of the recovery of injured bacteria using a fast dielectric spectroscopy. Klebsiella aerogenes (ATCC13048, Gram-negative) was used in this study. Bacterial solution containing calcium ions was exposed to a single PEF (600 ns, up to 32 kV/cm), and its dielectric property was measured using an impedance analyzer. Also, a numerical physical model of bacterial solution was made to calculate its dielectric property. The microscopic dielectric properties of bacterial membrane including permittivity and conductivity can be deduced by comparing the measured and the calculated dielectric properties over the frequency range between 1 and 10 MHz.

    The dielectric measurement indicates that the capacitance of the bacterial solution was decreased obviously by the exposure to PEF with a field strength of 8 kV/cm or higher, whereas the conductivity was increased. The decrease in the capacitance indicates the permeabilization of the bacterial membrane, while the increase in the conductance indicates both the permeabilization and the leakage of intracellular ionic material to the solution. At 9 kV/cm, which is little higher than the critical field strength, microscopic membrane permittivity was decreased once and subsequently returned to the value before the PEF exposure. This is the evidence that indicates the recovery of the electro-permeabilized membranes. For E > 10 kV/cm, the recovery was not detected.



    Topic 1:
    2. Biophysics and biochemistry of interaction mechanisms

    Topic 2:
    10. Food safety and food preservation

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