Kinetics of sterilization of Lactobacillus brevis cells by the application of high voltage pulses

Abstract

The technique of irreversible electroporation has been successfully applied to cause a lethal effect on Lactobacillus brevis cells suspended in phosphate buffer solution, Na₂HPO₄/NaH₂PO₄ · H₂O (0.845/0.186 mM) between parallel plane electrodes. Tests were carried out at different temperatures (24,45,60, and 80°C) to determine if there was a synergistic effect of temperature and electric pulse treatment on the destruction of L. brevis. Experimental results indicate that the viability (log N/N₀; where N₀ and N are the number of cells survived per milliliter before and after pulse voltage application, respectively) of L. brevis decreased with electric field strength E and temperature T and treatment time t_t. The relations between log(N/N₀) and t_t and log(N/N₀) and E indicate that higher field strengths are more effective than higher treatment times in causing destruction of L. brevis cells. It was also found that as the temperature of the liquid medium containing L. brevis cells increased from 24 to 60°C, the death rate of L. brevis cells increased with a decrease in the total treatment time t_t (pulse width × number of pulses applied). The application of an electric field strength E = 25 kV/cm at 60°C and treatment time t_t = 10 ms resulted in very high destruction levels of L. brevis cells (N/N₀ = 10⁻⁹). In comparison with existing steam sterilization technology, this new method of sterilization using relatively low temperature and short treatment time could prove to be an excellent method to minimize thermal denaturation of important nutrient components in liquid media. © John Wiley & Sons, Inc.