Inactivation of bacteria suspended in water by using high frequency unipolar pulse voltage

Food processing by pulsed electric field has received considerable attention in food and biotechnology. Although the PEF technology for bacterial inactivation depends upon both biological factors and electrical parameters, this article mainly focuses on the impact of pulse repetitive frequency on the bacterial inactivation suspended in liquid. This research work also aims to implement compact pulse converter technology using power MOSFETs to generate 1.5 kV unipolar pulses of width 1.2 μs at different pulse repetition frequency. The efficacy of the pulse generator was tested to inactivate Escherichia Coli MTCC 1610 strain suspended in water at 1, 10, 20, and 51 kHz at 15 kV/cm. It was observed that maximum of 4.4 log10 reduction of bacteria was achieved at 51 kHz (with 1,530,000 pulses) and about 1.2 log10 reduction achieved at 1 kHz (with 30,000 pulses). It shows that high repetitive frequency has significant impact on the process to inactivate the bacteria at moderate electric field intensity. Practical applications From the literature, it can be stated that the efficiency of inactivation process is determined by the amplitude of the pulsed electric field intensity. Ultimately this concept increases the cost of the PEF generator and complexity in circuit design. So, this work concentrates to bring down the electric field intensity without sacrificing the efficiency of the process by altering the pulse repetitive frequency among all other electrical parameters. The research also focuses to implement a bench scale PEF to inactivate bacteria in liquid food. The advancements in power semiconductor devices may help to improve the design of PEF generators and the developed PEF converter generates unipolar pulses of 1.5 kV at a variable frequency of 1 kHz to a maximum of 51 kHz with help of simple programmable microcontroller. This bench scale PEF converter is very compact. Since the pulse repetition frequency shows the significant log reduction, this helps to reduce the capital investment and has more options to scale up the design in pulsed power technology. With better power generators, after decades of research, PEF technology may finally be commercialized to inactivate bacteria.