Prevention Of Bubble Breakdown And Electrolysis In The Pulsed Electric Fields Treatment Chamber Assisted By Ultrasound And Microfluidics

Electroporation is the permeabilization of the cell membrane in response to the application of Pulsed electric fields(PEF)across the lipid bilayer,which can non-thermal sterilized the food without changing the flavor.For disinfecting the microbes effectively,especially in liquid food with high conductivity,the PEF treatment needs a very high electric field which may increase the current cross the treatment cham'ber.The large current will raise the temperature in the treatment chamber and the intensity of electrochemical reaction,even cause the bubble breakdown in the liquid food.Those side effect will not only affect the quality and safety of the food but also damage the PEF equipment.To solve those problems,we first studied the processing of the bubble breakdown and the mechanism of the bubble formation in very high electric fields based on a transparent co-linear treatment chamber.The results indicated that the number and size of the air bubble increase with the electric field.Partial discharge always happened in the edge of the treatment area when the electric field is between 20 kV/cm and 23.3 kV/cm,while totally breakdown may occur when the electric field became bigger.The total volume of the air increased with the conductivity of the NaCl solution,in which the percentage of the hydrogen risen from 1.35%to 12.35%.Therefore,to limit the induce of the air bubble,also,to avoid the local temperature rising,we should limit the density of the current flow through the chamber to limit the intensity of the electrochemical reaction.Based on the mechanism of bubble formation in the treatment chamber,we used ultrasound(US)to assist moderate PEF(12 kV/cm)to sterilize the food efficiently.The results showed that the combined treatment(US-PEF)had a synergetic effect,where the US-PEF's inactivation rate(3.48 log CFU/mL)is much higher than the inactivation rate of standalone US(0.76 log CFU/mL)and PEF(2.88 log CFU/mL).The result of microscope observation also proved this phenomenon that the microstructure of the cell treated by US-PEF was damaged more severely compared to the other two standalone treatments.Besides,the effect of the US-PEF on the quality of the Chinese rice wine was evaluated.It was found that the treatment did not affect the standard physiochemical properties and the color significantly.However,it will reduce the concentration of the volatile flavor compounds and increase the concentration of the metal ions(Fe,Cr,Ni)caused by the electrode corrosion.To limit the electrolysis in the treatment chamber and eliminate the electrode corrosion,we designed a non-electrolytic microelctroporation(NEME)chip which was constructed by planar metal electrodes coated with a thin layer of dielectric material.This thin layer of dielectric material isolated the metal elect-odes and the solution and also increased the resistance of the chamber.The finite element method simulation was used to analyze the effect of geometric parameters,material properties and the input voltage on the performance of the NEME chip which include the maximum electric fields(?E?max)and the area of the electric field bigger than 1 kV/cm(A1000).It was found that the ideal dielectric material is the material with very high permittivity and dielectric strength.Within a certain range,the higher permittivity,higher alternate current(AC)frequency,smaller electrodes gap and smaller conductivity of solution will induce bigger ?E?max and bigger A1000,until they reach saturations.On the other hand,we simulated the track of the yeast and E.coli flowing on the surface of the chip and found that the cells will experience electroporation and dielectrophoresis simultaneously which can be controlled by the frequency of AC.This phenomenon can be wildly applied to the separation of mixed cells and electroporated or killed the cell selectively.