INACTIVATION OF Yersinia enterocolitica GRAM-NEGATIV USING HIGH VOLTAGE PULSE TECHNIQU

Abstract- High voltage pulses of peak voltages U=5-75 kV and rise times tp=500-1300 ns were applied with repetition fre-quency f=lHz in order to cause the irreversible electroporation of Gram negative bacteria Yersiniu enterocolitica. The bacteria were suspended in NaCl solution of pH=7.2 and conductivity y ~0.8-1.3 S/m. The suspension was placed in glass tube im-mersed in the cylindrical electrode system gap filled with dis-tilled water. Such an electrode system will protect the bacteria suspension from the chemical processes a t the electrode-liquid interface due to conduction and prebreakdown phenomena. The current chopping electrode system was connected in paral-lel to the sample in order to avoid heat generation Bom direct discharge of the pulse through the suspension. The dependence of the survival ratio s=N/No (the number of bacteria per cm3 after pulse treatment, N, divided by the number of bacteria per cm3 before treatment, NJ of Y. enteruculiticu on peak voltage of the pulse, number of pulses applied and on various rise times of pulses have been measured. The reduction by 6 orders of magnitude of Y. enteroculitica living cells per cm3 was achieved. The results show that considerable inactivation of microbes can be achieved by the application of short (tp4000 ns) high voltage pulses for bacteria suspension without directly exposing the bacteria suspension to the electrodes. It is there-fore possible to use the electrode system proposed as a means for sterilization of liquid foods. 1