Liquid sterilization using intense electrical pulses combined with thermal post-treatment

This paper describes bacterial decontamination of liquid foods using intense pulsed electric fields (PEF) combined with a moderate thermal treatment (<;55°C), where most of ingredients remain unchanged. We have developed a one-way flow treatment system including a water-cooled parallel plane electrode and heat exchangers to control the liquid temperature. A 600 ns-long mono-polar rectangular pulse generated by a Blumlein type pulse-forming-network was delivered repetitively to the electrode. Saline solution including Enterobacter Aerogenes (E. Aerogenes) was exposed to tens of electrical pulses before the thermal treatment. Our experiment shows the additional thermal treatment strengthens the killing effect of the PEF treatment. The PEF treatment (50 kV/cm, 35 shots) at the room temperature reduced only 2 log in the bacterial population. The additional thermal treatment enhances the killing effect, and the additional killing effect linearly depends on the thermal treatment temperature within the experimental range between 25°C and 55°C, whereas E. Aerogenes survives the thermal treatment at 55°C. 7 log reduction in the population was achieved in this experiment. The bacterial death is considered to be caused by the heat influx due to the PEF-induced membrane disintegration.