Effect of temperature on survival rate in high electric field pulse sterilization

We have been studied the sterilization of liquid using high electric field pulse. In this paper, we report the effect of temperature on survival rate in high electric field pulse sterilization. The sample was liquid medium including E. coli (JM103). Experiments were carried out at two temperatures region, room temperature region (18~25 °C) and low temperature region (2~5°C). Effect of pulse interval between successive pulses was also examined at 60sec and 120sec. We obtained the results as follows: 1. The survival rate at low temperature region was higher than that at room temperature region. The low flexibility of cell membrane at low temperature is considered to be responsible for the high survival rate, because the stiff cell membrane has high resistivity against mechanical deformation due to the pulse shaped Maxwell stress. 2. At room temperature region, the survival rate after 50 pulses decreased to 0.69×10^-3 for 120sec interval ~ 2.9×10^-3 for 60sec interval. These rates clear a hygiene standard in Japan of 1.0×10^-2 for milk sterilization at 63°C for 30 minutes. 3. At low temperature region, the survival rate after 50 pulses stayed at the level of 1.2×10^-2 for 60sec interval ~ 7.4×10^-2 for 120sec interval.