Pulsed Electric Field Treatment Chamber Research Articles

Time-dependent model of temperature distribution in continuous flow pulsed electric field treatment chambers

A key component of a continuous flow pulsed electric field (PEF) system is the treatment chamber, where the product is exposed to electric pulses. Determination of the temperature distribution in the chamber during PEF treatment is important since high local increases in temperatures can affect the quality of the product. Coupled simulations of electric field, fluid flow, and heating in the existing literature do not model each individual electric pulse, but rather employ a “duty cycle” approach, which does not account for transient variations in treatment intensity and temperature changes in the medium. We present a time-dependent approach to modelling PEF treatment in continuous flow treatment chambers, which can model each pulse separately, and thus enables a more accurate study of temporal and spatial distributions of electric field and temperature. The model has been validated on laboratory scale treatment chambers of parallel plate or colinear design and using realistic protocols. Industrial relevance textThe paper is relevant to all pulsed electric field (PEF) applications either on laboratory or industrial scale that implement a continuous flow treatment chamber. It presents an improved modelling approach which allows for an analysis of the electrical current, electric field, and temperature distribution in the chamber during, at the end, and in between application of electrical pulses. The model can be used to predict the peak temperature at the end of each pulse in the hot spots, which if large enough could potentially lead to thermal damage of the product or in extreme cases even potential local boiling of the medium, resulting not only in degradation of the treated product, but also in accelerated electrode fouling, oxidation, and dissolution (etching), as well as arcing. This would not only affect the quality of the treated product but would also affect the wear and lifetime of electrodes/chambers, and of the pulse generator. The model can also be used to avoid expensive trial-and-error optimization of the PEF protocols and chamber geometries in situ.

Pulsed Electric Field Inactivation of Microorganism Using Chambers With Different Electrode Topologies

The effects of electrode topology on pulsed electric field (PEF) inactivation of microorganisms was investigated in the present study. Three PEF treatment chambers with different electrode topologies, which were parallel-plane, coaxial, and co-field respectively, were designed and built. PEF inactivation of yeast Saccharomyces cerevisiae suspension was conducted using these chambers with different electric field strength and a number of impulses. The performance of PEF inactivation was assessed by comparison of the population density of treated and untreated yeast samples. The results showed that the sterilization rate, as a function of the specific energy density, followed the same tendency regardless of the electrode topology, electric field strength, or the number of impulses. This strong correlation suggested that the specific energy density (energy per unit mass) could play a dominant role in the PEF inactivation of microorganisms once the threshold field strength was reached.

Optimization and simulation of pulsed electric field treatment chamber for food sterilization

Optimization and simulation of pulsed electric field treatment chamber for food sterilization

Selective Release of Recombinant Periplasmic Protein From E. coli Using Continuous Pulsed Electric Field Treatment.

To date, high-pressure homogenization is the standard method for cell disintegration before the extraction of cytosolic and periplasmic protein from E. coli. Its main drawback, however, is low selectivity and a resulting high load of host cell impurities. Pulsed electric field (PEF) treatment may be used for selective permeabilization of the outer membrane. PEF is a process which is able to generate pores within cell membranes, the so-called electroporation. It can be readily applied to the culture broth in continuous mode, no additional chemicals are needed, heat generation is relatively low, and it is already implemented at industrial scale in the food sector. Yet, studies about PEF-assisted extraction of recombinant protein from bacteria are scarce. In the present study, continuous electroporation was employed to selectively extract recombinant Protein A from the periplasm of E. coli. For this purpose, a specifically designed flow-through PEF treatment chamber was deployed, operated at 1.5 kg/h, using rectangular pulses of 3 μs at specific energy input levels between 10.3 and 241.9 kJ/kg. Energy input was controlled by variation of the electric field strength (28.4–44.8 kV/cm) and pulse repetition frequency (50–1,000 Hz). The effects of the process parameters on cell viability, product release, and host cell protein (HCP), DNA, as well as endotoxin (ET) loads were investigated. It was found that a maximum product release of 89% was achieved with increasing energy input levels. Cell death also gradually increased, with a maximum inactivation of -0.9 log at 241.9 kJ/kg. The conditions resulting in high release efficiencies while keeping impurities low were electric field strengths ≤ 30 kV/cm and frequencies ≥ 825 Hz. In comparison with high-pressure homogenization, PEF treatment resulted in 40% less HCP load, 96% less DNA load, and 43% less ET load. Therefore, PEF treatment can be an efficient alternative to the cell disintegration processes commonly used in downstream processing.

Pulsed electric field-assisted fermentation of Hanseniaspora sp. yeast isolated from Lebanese apples.

Hanseniaspora sp. yeast was stimulated using pulsed electric field (PEF) during the different fermentation phases. The impact of PEF parameters on the growth rate and substrate consumption was studied. The PEF intensities chosen for this study were mainly in the range of 72-285V cm-1. A PEF treatment chamber was designed for this study with a ratio of 1:50 between the volume of the fermenter and the volume of the chamber. It allows the recycling of the culture medium using a peristaltic pump, and the yeast treatment by PEF during the fermentation. The continuous circulation of the medium allows avoiding the increase of the temperature inside the fermenter, the cell aggregation, as well as the agitation and the scale-up issues that are associated with the PEF treatment of the entire volume in batch mode. The maximal yeast growth rate was obtained using an electric field strength of 285V cm-1 applied during both Lag and early exponential phase, and Log phase. This observation was accompanied by a faster consumption of glucose in the medium during the fermentation. Besides, the sensitivity of Hanseniaspora sp. yeast to PEF treatment was more pronounced during the Lag and early exponential phase than the Log phase. The results obtained exposed the great benefit of stimulating Hanseniaspora sp. yeast using moderate PEF as it reduces the fermentation time along with increasing the biomass concentration.

Continuously pulsed electric field treatment chamber modelling and design

The perspectives of pulsed electric field (PEF) application for rheological changes in plant materials and treatment chamber design are considered in current paper. By using some mathematical tools and experiments data, viscosity of transporting plant materials confirms proposed Bingham rheological model assumption. Experimental studies have shown the presence of structure formation in material supplied to the treatment chamber channel. An effect of PEF treatment, with changes of material structure and increasing of material plastic viscosity from 0.117 to 0.159 Pa·s for samples after treatment by a field strength of E = 8 kV/cm and the number of pulses n = 300 was found. Obtained results of pulsed electric fields application in continuously material flow can be used in pulsed electric fields technologies, equipment design and help to determine cost efficiency of treatment in industrial application.

Comprehensive pulsed electric field (PEF) system analysis for microalgae processing

Pulsed electric field (PEF) is an emerging nonthermal technique with promising applications in microalgae biorefinery concepts. In this work, the flow field in continuous PEF processing and its influencing factors were analyzed and energy input distributions in PEF treatment chambers were investigated. The results were obtained using an interdisciplinary approach that combined multiphysics simulations with ultrasonic Doppler velocity profiling (UVP) and rheological measurements of Arthrospira platensis suspensions as a case study for applications in the biobased industry. UVP enabled non-invasive validation of multiphysics simulations. A. platensis suspensions follow a non-Newtonian, shear-thinning behavior, and measurement data could be fitted with rheological functions, which were used as an input for fluid dynamics simulations. Within the present work, a comprehensive system characterization was achieved that will facilitate research in the field of PEF processing.

Study and analysis of new pulsed electric field treatment chamber configurations for food extraction

In all treatment chamber (TC) models used in industry and in research laboratories, the product to be treated is placed in one volume unit delimited between two electrodes energized by a pulsed voltage and the electric field lines are monoaxial and perpendicular to the electrodes. The objective of this paper is to perform an experimental analysis, based on the pulsed electric field-treated beet juice extraction efficiency, of two TC new configurations. The first model is constituted of one, two, or three parallel PEF units comprising several alternate ground-HV electrodes. The treatment chambers made of Plexiglas have a square parallelepipedic shape, in which are placed two (TC$_{1})$, three (TC$_{2})$, or five (TC$_{3})$ vertical and parallel stainless steel electrodes. The second biaxial treatment chamber model is constituted of four identical stainless steel electrodes placed on the side walls of a square shape treatment chamber made of Plexiglas of the same dimensions as the first model. For this latter, each pair of adjacent metal plates forms one electrode. The obtained results expressed in terms of extracted juice mass, betanin concentration by measuring the absorbance, and energy consumption have shown that the models TC$_{3}$ and TC$_{4}$ are much better due to the higher values of the electric field for the same applied voltage.

Engineering of operation condition in milk pasteurization with PEF treatment

We propose a new continuous pasteurization technique for milk that involves pulsed electric field (PEF) treatment with a voltage of 40 kVp and a frequency of 100 Hz. Escherichia coli with an initial concentration 107 cells/mL that was suspended in commercial milk was used as the target microorganism. Without control of the milk temperature, an average holding time in PEF treatment of 20 s should be necessary for the efficient inactivation of E. coli suspended in milk. Thermal control was incorporated in our system to improve the productivity and stability of the pasteurization process. Sufficient inactivation of E. coli cells was found to be possible even with an average holding time in PEF treatment of 10 s at a milk temperature of 50 °C or higher. We proposed a system for the PEF pasteurization of milk, in which a preheating unit and postholding unit were incorporated. When the milk temperature at the inlet of the PEF treatment chamber was controlled at 60 °C using preheating unit and the milk temperature after the PEF treatment was held at 70 °C for 20 s using the postholding unit, a reduction in the CFU of E. coli cells suspended in milk of at least seven orders of magnitude was achieved in our continuous PEF inactivation system.

On the modeling of electrochemical phenomena at the electrode-solution interface in a PEF treatment chamber: Methodological approach to describe the phenomenon of metal release

In pulsed electric field (PEF) processing of liquid foods, unavoidable electrochemical reactions occur, including those involving metal release from the electrodes, which may seriously affect food safety and quality as well as the electrode’s lifetime.The aim of this paper was to set up a mathematical model describing the phenomenon of the metal release from stainless steel (type AISI 316L) electrodes of a continuous flow parallel plate PEF treatment chamber into model liquid foods. The effect of PEF processing variables such as electric field strength, total specific energy input and treatment medium composition on the dynamics of the spatial distribution of the main metallic elements (Fe, Cr and Ni) released from the electrodes in the treatment volume as well as their concentration in the bulk of the product exiting the treatment chamber were simulated. All simulations were performed using a FEM based commercial software (COMSOL Multiphysics™). A validation of the predicted results was carried out and it was demonstrated that the model set up accurately describes phenomenon of metal release at the electrode solution interface.

Influencing Factors of Dielectric Breakdown in the PEF Treatment Chamber

Electrical breakdown of the treatment chambers under repetitive high-intensity pulses impedes the industrial application of pulsed electric field (PEF) technology. In this paper, phenomenon and laws of electric discharges in the PEF treatment chambers were studied. The experimental results indicate that temperature increase and formation of gas bubbles under high electric field strength reduces insulation of water solution. Air dissolved in the samples is only a small part of the bubble and hardly affects the size of bubble formed. The majority part of the gas in the bubble comes from the vaporization of liquid. Fluctuations in the temperature curve may be a direct indication of the beginning of bubble formation. Partial electrical discharges occur inside the gas bubble and are the precursor of dielectric breakdown of PEF treatment chambers. Solution temperature and conductivity have significant effect on electrical discharges. Electric field strength needed for the electrical discharge decreases as the initial temperature increases. As the solution conductivity increases, the lowest electric field strength required for electrical discharge occurrence decreases. Findings in the present investigation reveal that measures that help to reduce the bubble formation are helpful to safe operation of the PEF system.

Research Status of High-Intensity Pulsed Electric Field (PEF) Equipment and its Application on Food Processing

Due to short treatment time, the quality change of food caused by heat can be reduced, high-intensity pulsed electric field (PEF) has been widely used, especially in food industry. PEF system consists of PEF generator, treatment chamber, pump, cooling coil, container and monitoring system. The research status of PEF generator, pulses waveforms, treatment chamber and electrodes were discussed. And the application of PEF on food processing was summarized.

Coupled Simulations in Colinear and Coaxial Continuous Pulsed Electric Field Treatment Chambers

Abstract. Pulsed electric field (PEF) treatment is an emerging non-thermal pasteurization technology for maintaining the safety and quality of food. As a key component of PEF technology, the treatment chamber should offer a homogeneous treatment condition for effective microbial inactivation. In this study, multiphysics simulations of the PEF process were developed to quantify the electric field, fluid flow characteristics, and heat transfer in colinear and coaxial treatment chambers. In addition, experiments on PEF pasteurization of watermelon juice in the two tested treatment chambers were carried out to measure the outlet temperature and microbial reduction rate. Based on the simulation results, Hulsheger’s kinetic model was used to predict microbial inactivation in the watermelon juice. The simulation results showed higher electric field intensity and less temperature increase in the coaxial treatment chamber. The outlet temperatures in the two tested treatment chambers were well predicted by numerical simulations, with coefficients of determination (R 2 ) of 0.998 and 0.995 between measured and predicted values for the colinear and coaxial treatment chambers, respectively. In the coaxial treatment chamber, the calculated results better fitted the survival curves of total aerobic plate count and yeast and mold counts, with R 2 = 0.975 and 0.981, respectively, compared to R 2 = 0.989 and 0.883 in the colinear treatment chamber. Numerical simulation of the PEF process is useful in optimizing the geometry of PEF treatment chambers and in determining the effectiveness of microbial inactivation.

Modelling of polyphenoloxidase inactivation by pulsed electric fields considering coupled effects of temperature and electric field

Thermal effects can strongly influence the impact of pulsed electric field (PEF) treatment on enzyme inactivation. Most of the kinetic models found in literature, do not distinguish between PEF and thermal effects. A batch PEF treatment chamber with temperature control was used in order to allow performance of PEF treatments at quasi-isothermal conditions. An empirical model describing the PEF polyphenoloxidase (PPO) inactivation as a function of the electric field strength, temperature, treatment time, residence time and synergistic effects of electric field strength and temperature was developed. Experimental data showed that PPO was not inactivated by PEF treatments at temperatures below 55 °C and thermal inactivation seems to be significant at temperatures between 59 and 67 °C. However, PPO activity decreased down to 60% when PEF treatments were applied at temperatures in the range of 55 to 59 °C. The synergistic effect of PEF and temperature was described by a kinetic model at different treatment temperatures. Kinetic models to describe the inactivation of enzymes as a function of PEF parameters, such as electric field strength and treatment time have already been developed. However, these models do not consider the temperature as a variable within the kinetic model. In the present study, a kinetic model was developed, which includes the synergistic effect between temperature and electric field strength. This allows quantifying the PPO inactivation under different processing temperatures and may serve as a base to set up experimental trials whereas a certain temperature is desired.

Minimization of Thermal Impact by Application of Electrode Cooling in a Co‐linear PEF Treatment Chamber

A co-linear pulsed electric field (PEF) treatment chamber was analyzed and optimized considering electrical process conditions, temperature, and retention of heat-sensitive compounds during a continuous PEF treatment of peach juice. The applicability of a jacket heat-exchanger device surrounding the ground electrode was studied in order to provide active cooling and to avoid temperature peaks within the treatment chamber thus reducing the total thermal load to which the product is exposed. Simulation of the PEF process was performed using a finite element method prior to experimental verification. Inactivation of polyphenoloxydase (PPO) and peroxidase (POD) as well as the degradation of ascorbic acid (AA) in peach juice was quantified and used as indirect indicators for the temperature distribution. Peaks of product temperature within the treatment chamber were reduced, that is, from 98 to 75 °C and retention of the indicators PPO, POD, and AA increased by more than 10% after application of the active electrode cooling device. Practical Application: The co-linear PEF treatment chamber is widely used for continuous PEF treatment of liquid products and also suitable for industrial scale application; however, Joule heating in combination with nonuniform electric field distribution may lead to unwanted thermal effects. The proposed design showed potential to reduce the thermal load, to which the food is exposed, allowing the retention of heat-sensitive components. The design is applicable at laboratory or industrial scale to perform PEF trials avoiding temperature peaks, which is also the basis for obtaining inactivation kinetic models with minimized thermal impact on the kinetic variables.

An iterative modelling approach for improving the performance of a pulsed electric field (PEF) treatment chamber

An important component of the pulsed electric field (PEF) technology is the treatment chamber in which the food is exposed to high voltage pulses. Non-uniformity of the treatment, particularly with respect to the electric field distribution, is a common problem in continuous PEF treatment chambers. A previously developed and validated Multiphysics model of a pilot-scale PEF system with co-linear electrode configuration was simplified and embedded into an iterative algorithm, automatically modifying the model's treatment chamber geometry and dimensions, and evaluating the simulated process with respect to a set of performance indicators. The algorithm was capable of identifying configurations that were superior to the standard co-linear treatment chamber configuration. A 3D Multiphysics model with the identified geometrical properties was developed and a corresponding treatment chamber manufactured. The Multiphysics model was validated by comparing measured and predicted temperatures at various process conditions induced in NaCl solution and apple juice.

Effect of dimensions and geometry of co-field and co-linear pulsed electric field treatment chambers on electric field strength and energy utilisation

Approximations of the electric field strength and specific energy input of continuous pulsed electric field (PEF) systems often assume parallel plate configurations. However, it is known that actual electric field strengths and specific energy inputs can be significantly different from this simplistic approach. A systematic study of more than 150 dimensions and various insulator geometries of pilot-scale PEF treatment chambers with co-linear electrode configuration was performed. A reduction of the inner diameter of the insulator and its shape changes the distribution and (average) intensity of the electric field. Both, the average electric field strength of the PEF treatment zone and the actual specific energy input, were significantly lower than the expected values derived from dividing the applied voltage by the electrode gap. The difference between theoretical and actual values generally increased with increasing electrode radius and decreasing electrode gap. The relative ratios of theoretical electric field strength or specific energy input to actual (average) electric field strength or specific energy input showed a linear dependency on the ratio of electrode radius and gap. The determined relationships of specific energy input and treatment chamber dimensions and geometry were experimentally validated in four different PEF treatment chambers.

An investigation on pulsed electric fields technology using new treatment chamber design

A pulsed electric field (PEF) system was designed and constructed using modern IGBT technology. The main focus of this work was to design a new PEF treatment chamber that operate at high electric field intensities with limited increase in liquid temperature and limited fouling of electrodes. Four multi-pass treatment chambers were designed consisting of two stainless steel mesh electrodes in each chamber, with the treated fluid flowing through the openings of the mesh electrodes. The two electrodes are electrically isolated from each other by an insulator element designed to form a small orifice where most of the electric field is concentrated. Dielectric breakdown inside the chambers was prevented by removing the electrodes far from the narrow gap. The effect of PEF treatment on the inactivation of gram-negative Escherichia coli ATCC 25922 suspended in simulated milk ultra-filtrate (SMUF) of 100%, 66.67% and 50% w/w was investigated. Treatments with the same electrical input power but with higher electric field strengths provided larger degree of killing. The effect of PEF treatment using suspensions at different flow rates and different pulse frequencies was also investigated. In general, the inactivation rate of E. coli increased with increasing electric field strength, treatment time and processing temperature. More than 6 log reductions in E. coli suspended in SMUF was achieved using electric field intensity in the range of (37.2–49.6 kV/cm) with a treatment temperature not exceeding 38 °C.

Transient electrical field across cellular membranes: pulsed electric field treatment of microbial cells

The pulsed electric field (PEF) treatment of liquid and pumpable products contaminated with microorganisms has attracted significant interest from the pulsed power and bioscience research communities particularly because the inactivation mechanism is non-thermal, thereby allowing retention of the original nutritional and flavour characteristics of the product. Although the biological effects of PEF have been studied for several decades, the physical mechanisms of the interaction of the fields with microorganisms is still not fully understood. The present work is a study of the dynamics of the electrical field both in a PEF treatment chamber with dielectric barriers and in the plasma (cell) membrane of a microbial cell. It is shown that the transient process can be divided into three physical phases, and models for these phases are proposed and briefly discussed. The complete dynamics of the time development of the electric field in a spherical dielectric shell representing the cellular membrane is then obtained using an analytical solution of the Ohmic conduction problem. It was found that the field in the membrane reaches a maximum value that could be two orders of magnitude higher than the original Laplacian electrical field in the chamber, and this value was attained in a time comparable to the field relaxation time in the chamber. Thus, the optimal duration of the field during PEF treatment should be equal to such a time.

Effects of Pulsed Electric Fields on the Activity and Structure of Pepsin

A continuous pulsed electric field (PEF) system integrated with six co-field flow PEF treatment chambers was used to study the inactivation of pepsin. The inactivation of pepsin activity was a function of applied electric field strength, electrical conductivity, and pH. The inactivation of pepsin by PEF followed a first-order model. The first-order inactivation kinetic constant of pepsin was 0.012 (1/mus) in 7.5 mM HCl (pH 2.0) at 34.2 kV/cm. Aggregation of pepsin was observed during PEF treatment; however, the inactivation took place before the formation of aggregates. Circular dichroism analysis showed that inactivation of pepsin by PEF was correlated to the loss of beta-sheet structure in a pepsin molecule. The relative residual activity of PEF-treated pepsin was correlated to the relative molar ellipticity at 215 nm. Both PEF- and heat-induced inactivation of pepsin were correlated with the alteration of the secondary structure (beta-sheet dominant structure) of pepsin.