Behavior of yeast cells in aqueous suspension affected by pulsed electric field

This work discusses pulsed electric fields (PEF) induced effects in treatment of aqueous suspensions of concentrated yeast cells (S. cerevisiae  ). The PEF treatment was done using pulses of near-rectangular shape, electric field strength was within E=2–5 kV/cmE=2–5 kV/cm and the total time of treatment was tPEF=10−4–0.1 stPEF=10−4–0.1 s. The concentration of aqueous yeast suspensions was in the interval of CY=0–22CY=0–22 (wt%), where 1% concentration corresponds to the cellular density of 2×108 cells/mL2×108 cells/mL. Triton X-100 was used for studying non-ionic surfactant additive effects. The electric current peak value I was measured during each pulse application, and from these data the electrical conductivity σ was estimated. The PEF-induced damage results in increase of σ   with tPEFtPEF increasing and attains its saturation level σ≈σmaxσ≈σmax at long time of PEF treatment. The value of σmaxσmax reflects the efficiency of damage. The reduced efficiency of damage at suspension volume concentration higher than φY≈32 vol%φY≈32 vol% is explained by the percolation phenomenon in the randomly packed suspension of near-spherical cells. The higher cytoplasmic ions leakage was observed in presence of surfactant. Experiments were carried out in the static and continuous flow treatment chambers in order to reveal the effects of mixing in PEF-treatment efficiency. A noticeable aggregation of the yeast cells was observed in the static flow chamber during the PEF treatment, while aggregation was not so pronounced in the continuous flow chamber. The nature of the enhanced aggregation under the PEF treatment was revealed by the ζ-potential measurements: these data demonstrate different ζ-potential signs for alive and dead cells. The effect of the electric field strength on the PEF-induced extraction of the intracellular components of S. cerevisiae is discussed.

This work discusses the PEF induced effects in treatments of concentrated yeast cells (S. cerevisiae) aqueous suspensions. The nature of enhanced aggregation under the PEF treatment was revealed by the measurements of ζ-potentials: the data evidence the difference of ζ-potential signs between alive and dead cells.Figure optionsDownload as PowerPoint slide