Effect of culture temperature on high-voltage pulse sterilization of Escherichia coli

The effect of culture temperature of Escherichia coli on pulsed electric field (PEF) sterilization has been studied. PEF sterilization, which is a method of inactivation of cells by a high-voltage pulsed electric field, was used. The E. coli cells cultivated at 20°C, 30°C, 37°C, and 42°C, respectively, were collected and homogenous PEF of 16 kV/cm and 50 Hz was applied at various temperatures. When the E. coli cells were cultivated at 20°C or 42°C, the cells were more easily sterilized by PEF sterilization than the E. coli cells cultivated at 37°C, which is the optimal culture temperature of E. coli. The survival ratio after a dose of 100 J/ml of PEF at 50°C was about 10−2 and 10−3 as the E. coli cells were cultivated at 30°C or 37°C and 20°C or 42°C, respectively. These results indicate that the sterilization efficiency is dependent on the culture temperature even if the same bacteria are used. The death rates of the E. coli cells under various conditions were shown in a form of an Arrhenius plot. It was revealed that the efficiency of PEF sterilization is influenced by the PEF treatment temperature and this dependence changes between 30°C and 40°C of PEF treatment temperature. Moreover, the death rate of bacteria was found to be considerably influenced by the culture temperature of the E. coli cells. The E. coli cells cultivated at 37°C were practically resistant against PEF sterilization, while the cells cultivated at 20°C or 42°C were easily killed. Our results suggested that it is important to check the culture temperature of treated bacteria if PEF sterilization is applied in the industry.