ΠΑΠΙΜΙ

 Microbial Inactivation

with induced electric currents type of PAPIMI

Scientific Studies

Biotechnol Bioeng. 1992 Dec 20;40(11):1412-20.
Kinetics of sterilization of Lactobacillus brevis cells by the application of high voltage pulses.
Jayaram S, Castle GS, Margaritis A.

The technique of irreversible electroporation has been successfully applied to cause a lethal effect on Lactobacillus
brevis cells suspended in phosphate buffer solution, Na(2)HPO(4)/NaH(2)PO(4) . H(2)O (0.845/0.186 mM) between parallel plane
electrodes. Tests were carried out at different temperatures (24,45,60, and 80 degrees C) to determine if there was a
synergistic effect of temperature and electric pulse treatment on the destruction of L. brevis. Experimental results indicate
that the viability (log N/N(0); where N(0) and N are the number of cells survived per milliliter before and after pulse
voltage application, respectively) of L. brevis decreased with electric field strength E and temperature T and treatment time
t(t). The relations between log(N/N(0)) and t(t) and log(N/N(0)) and E indicate that higher field strengths are more
effective than higher treatment times in causing destruction of L. brevis cells. It was also found that as the temperature of
the liquid medium containing L. brevis cells increased from 24 to 60 degrees C, the death rate of L. brevis cells increased
with a decrease in the total treatment time t(t) (pulse width x number of pulses applied). The application of an electric
field strength E = 25 kV/cm at 60 degrees C and treatment time t(t) = 10 ms resulted in very high destruction levels of L.
brevis cells (N/N(0) = 10(-9)). In comparison with existing steam sterilization technology, this new method of sterilization
using relatively low temperature and short treatment time could prove to be an excellent method to minimize thermal
denaturation of important nutrient components in liquid media. (c) John Wiley & Sons, Inc.

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Appl Microbiol Biotechnol. 1996 Mar;45(1-2):148-57.
Killing of microorganisms by pulsed electric fields.
Grahl T, Märkl H.

Lethal effects of pulsed electric fields (PEF) on suspensions of various bacteria, yeast, and spores in buffer solutions
and liquid foodstuffs were examined. Living-cell counts of vegetative cell types were reduced by PEF treatment by up to more
than four orders of magnitude (> 99.99%). On the other hand, endo- and ascospores were not inactivated or killed to any great
extent. The killing of vegetative cell types depends on the electrical field strength of the pulses and on the treatment time
(the product of the pulse number and the decay time constant of the pulses). For each cell type, a specific critical electric
field strength (Ec) and a specific critical treatment time (tc) were determined. Above these critical values, the fractions
of surviving cells were reduced drastically. The "limits" Ec and tc depend on the cell characteristics as well as on the type
of medium in which the cells are suspended. Especially in acid media living-cell counts were sufficiently decreased at very
low energy inputs. In addition to the inactivation of microorganisms, the effect of PEF on food components such as whey
proteins, enzymes and vitamins, and on the taste of foodstuffs was studied. The degree of destruction of these food
components by PEF was very low or negligible. Moreover, no significant deterioration of the taste of foodstuffs was detected
after PEF treatment. Disintegration of cells by PEF treatment in order to harvest intracellular products was also studied.
Yeast cells, suspended in buffer solution, were not disintegrated by electric pulses. Hence, PEF treatment is an excellent
process for inactivation of microorganisms in acid and in thermosensive media, but not for complete disintegration of
microbial cells.

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Crit Rev Food Sci Nutr. 1996 Jul;36(6):603-27.
Nonthermal pasteurization of liquid foods using high-intensity pulsed electric fields.
Qin BL, Pothakamury UR, Barbosa-Cánovas GV, Swanson BG.

Processing foods with high-intensity pulsed electric fields (PEF) is a new technology to inactivate microorganisms and
enzymes with only a small increase in food temperature. The appearance and quality of fresh foods are not altered by the
application of PEF, while microbial inactivation is caused by irreversible pore formation and destruction of the
semipermeable barrier of the cell membrane. High-intensity PEF provides an excellent alternative to conventional thermal
methods, where the inactivation of the microorganisms implies the loss of valuable nutrients and sensory attributes. This
article presents recent advances in the PEF technology, including microbial and enzyme inactivation, generation of pulsed
high voltage, processing chambers, and batch and continuous systems, as well as the theory and its application to food
pasteurization. PEF technology has the potential to improve economical and efficient use of energy, as well as provide
consumers with minimally processed, microbiologically safe, nutritious and freshlike food products.

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J Food Prot. 1999 Sep;62(9):1088-96.
Pulsed electric field processing of foods: a review.
Jeyamkondan S, Jayas DS, Holley RA.

Use of pulsed electric fields (PEFs) for inactivation of microorganisms is one of the more promising nonthermal
processing methods. Inactivation of microorganisms exposed to high-voltage PEFs is related to the electromechanical
instability of the cell membrane. Electric field strength and treatment time are the two most important factors involved in
PEF processing. Encouraging results are reported at the laboratory level, but scaling up to the industrial level escalates
the cost of the command charging power supply and of the high-speed electrical switch. In this paper, we critically review
the results of earlier experimental studies on PEFs and we suggest the future work that is required in this field.
Inactivation tests in viscous foods and in liquid food containing particulates must be conducted. A successful continuous PEF
processing system for industrial applications has yet to be designed. The high initial cost of setting up the PEF processing
system is the major obstacle confronting those who would encourage the system's industrial application. Innovative
developments in high-voltage pulse technology will reduce the cost of pulse generation and will make PEF processing
competitive with thermal-processing methods.

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Int J Food Microbiol. 2000 Mar 10;54(1-2):91-8.
Pulsed electric fields inactivation of attached and free-living Escherichia coli and Listeria innocua under several conditions.
Dutreux N, Notermans S, Wijtzes T, Góngora-Nieto MM, Barbosa-Cánovas GV, Swanson BG.

The use of pulsed electric fields (PEF) is considered as a mild process in the inactivation of microorganisms present in
liquid food products. PEF treatments of Escherichia coli and Listeria innocua suspended in milk and phosphate buffer, with
same pH and same conductivities, yielded to similar inactivation. Reduction rates obtained in distilled water indicated that
conductivity of the food product is a main parameter in bacterial inactivation. Bacteria attached to polystyrene beads were
inactivated by PEF at a greater (E. coli) or equal rate (L. innocua) than free-living bacteria. Base on the use of selective
and non-selective enumeration media, no clear indications were obtained for sublethal damage of microorganisms surviving the
PEF treatment. E. coli cells subjected to 60 pulses at 41 kV/cm were examined by transmission and scanning electron
microscopy. Changes in the cytoplasm were observed and the cell surface appeared rough. The cells outer membranes were
partially destroyed allowing leaking of cell cytoplasm.

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Radiat Environ Biophys. 1981;20(1):53-65.
Killing of bacteria with electric pulses of high field strength.
Hülsheger H, Potel J, Niemann EG.

Bacteria of the type E. coli K12 have been treated in experiments using high-voltage pulses of short time (microseconds)
as a killing agent. The role of different experimental parameters has been studied: kind of electrolyte, concentration,
length of pulses, field strength, pH and temperature. Electrolytes with bivalent cations were found to reduce the lethal
action. the relative rate of killed bacteria was shown to be mainly governed by the field strength and the treatment time,
which is defined by the product of pulse number and decay time constant. From the obtained results a function has been
developed which enables the precalculation of the killing rate for E. coli, provided that certain limits of experimental
conditions are considered. No correlation between the applied electric energy and the lethal effect could be found.

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Radiat Environ Biophys. 1980;18(4):281-8.

Lethal effects of high-voltage pulses on E. coli K12.

Hülsheger H, Niemann EG.

The lethal effects of high-voltage capacitor-discharges in suspensions of E. coli K12 with varying electrolytes have been examined. A reduction of more than 99.9% of living cells, dependent on the applied voltage could be proved. The bactericidal action is assumed to be due to direct effects of high electric fields. Electrolytically produced chlorine was shown to act as an additional toxic agent, when chloride is present in the treated medium. The relative survival rate of bacteria has been found to depend also on the concentration of cells during pulse treatment.

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Appl Microbiol Biotechnol. 1996 Mar;45(1-2):148-57.

Killing of microorganisms by pulsed electric fields.

Grahl T, Märkl H.

Technische Universität Hamburg-Harburg, Germany.

Lethal effects of pulsed electric fields (PEF) on suspensions of various bacteria, yeast, and spores in buffer solutions and liquid foodstuffs were examined. Living-cell counts of vegetative cell types were reduced by PEF treatment by up to more than four orders of magnitude (> 99.99%). On the other hand, endo- and ascospores were not inactivated or killed to any great extent. The killing of vegetative cell types depends on the electrical field strength of the pulses and on the treatment time (the product of the pulse number and the decay time constant of the pulses). For each cell type, a specific critical electric field strength (Ec) and a specific critical treatment time (tc) were determined. Above these critical values, the fractions of surviving cells were reduced drastically. The "limits" Ec and tc depend on the cell characteristics as well as on the type of medium in which the cells are suspended. Especially in acid media living-cell counts were sufficiently decreased at very low energy inputs. In addition to the inactivation of microorganisms, the effect of PEF on food components such as whey proteins, enzymes and vitamins, and on the taste of foodstuffs was studied. The degree of destruction of these food components by PEF was very low or negligible. Moreover, no significant deterioration of the taste of foodstuffs was detected after PEF treatment. Disintegration of cells by PEF treatment in order to harvest intracellular products was also studied. Yeast cells, suspended in buffer solution, were not disintegrated by electric pulses. Hence, PEF treatment is an excellent process for inactivation of microorganisms in acid and in thermosensive media, but not for complete disintegration of microbial cells.

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J Appl Microbiol. 2003;94(4):571-9.

Modelling and optimization of inactivation of Lactobacillus plantarum by pulsed electric field treatment.

Abram F, Smelt JP, Bos R, Wouters PC.

Food Processing Group, Unilever Research & Development Vlaardingen, The Netherlands.

AIMS: The effect of critical pulsed electric field (PEF) process parameters, such as electric field strength, pulse length and number of pulses, on inactivation of Lactobacillus plantarum was investigated. METHODS AND RESULTS: Experiments were performed in a pH 4.5 sodium phosphate buffer having a conductivity of 0.1 S m-1, using a laboratory-scale continuous PEF apparatus with a co-linear treatment chamber. An inactivation model was developed as a function of field strength, pulse length and number of pulses. Based on this inactivation model, the conditions for a PEF treatment were optimized with respect to the minimum energy required to obtain a certain level of inactivation. It was shown that the least efficient process parameter in the range investigated was the number of pulses. The most efficient way to optimize inactivation of Lact. plantarum was to increase the field strength up to 25.7 kV cm-1, at the shortest pulse length investigated, 0.85 micros, and using a minimum number of pulses. The highest inactivation of Lact. plantarum at the lowest energy costs is obtained by using the equation: E=26.7tau0.23, in which E is the field strength and tau the pulse length. An optimum is reached by substituting tau with 5.1. CONCLUSIONS: This study demonstrates that the correct choice of parameters, as predicted by the model described here, can considerably improve the PEF process. SIGNIFICANCE AND IMPACT OF THE STUDY: The knowledge gained in this study improves the understanding of the limitations and opportunities of the PEF process. Consequently, the advantage of the PEF process as a new option for non-thermal decontamination can be better utilized.

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J Food Prot. 2001 Jul;64(7):964-9.

Reduction in levels of Escherichia coli O157:H7 in apple cider by pulsed electric fields.

Iu J, Mittal GS, Griffiths MW.

Department of Food Science, University of Guelph, Ontario, Canada.

Many studies have demonstrated that high voltage pulsed electric field (PEF) treatment has lethal effects on microorganisms including Escherichia coli O157:H7; however, the survival of this pathogen through the PEF treatment is not fully understood. Fresh apple cider samples inoculated with E. coli O157:H7 strain EC920026 were treated with 10, 20, and 30 instant charge reversal pulses at electric field strengths of 60, 70, and 80 kV/cm, at 20, 30, and 42 degrees C. To accurately evaluate the lethality of apple cider processing steps, counts were determined on tryptic soy agar (TSA) and sorbitol MacConkey agar (SMA) to estimate the number of injured and uninjured E. coli O157:H7 cells after PEF treatment. Cell death increased significantly with increased temperatures and electric field strengths. A maximum of 5.35-log10 CFU/ml (P < 0.05) reduction in cell population was achieved in samples treated with 30 pulses and 80 kV/cm at 42 degrees C. Cell injury measured by the difference between TSA and SMA counts was found to be insignificant (P > 0.05). Under extreme conditions, a 5.91-log10 CFU/ml reduction in cell population was accomplished when treating samples with 10 pulses and 90 kV/cm at 42 degrees C. PEF treatment, when combined with the addition of cinnamon or nisin, triggered cell death, resulting in a reduction in E. coli O157:H7 count of 6 to 8 log10 CFU/ml. Overall, the combination of PEF and heat treatment was demonstrated to be an effective pasteurization technique by sufficiently reducing the number of viable E. coli O157:H7 cells in fresh apple cider to meet U.S. Federal Drug Administration recommendations.

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 J Food Prot. 1999 Jul;62(7):793-6.

Inactivation of Escherichia coli O157:H7 and Escherichia coli 8739 in apple juice by pulsed electric fields.

Evrendilek GA, Zhang QH, Richter ER.

Department of Food Science and Technology, The Ohio State University, Columbus 43210, USA.

The effect of high voltage pulsed electric field (PEF) treatment on Escherichia coli O157:H7 and generic E. coli 8739 in apple juice was investigated. Fresh apple juice samples inoculated with E. coli O157:H7 and E. coli 8739 were treated by PEF with selected parameters including electric field strength, treatment time, and treatment temperature. Samples were exposed to bipolar pulses with electric field strengths of 30, 26, 22, and 18 kV/cm and total treatment times of 172, 144, 115, and 86 micros. A 5-log reduction in both cultures was determined by a standard nonselective medium spread plate laboratory procedure. Treatment temperature was kept below 35 degrees C. Results showed no difference in the sensitivities of E. coli O157:H7 and E. coli 8739 against PEF treatment. PEF is a promising technology for the inactivation of E. coli O157:H7 and E. coli 8739 in apple juice.

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Int J Food Microbiol. 2000 Apr 10;55(1-3):143-6.

Influence of different factors on the inactivation of Salmonella senftenberg by pulsed electric fields.

Alvarez I, Raso J, Palop A, Sala FJ.

Tecnología de los Alimentos, Dpto. PACA, Facultad de Veterinaria, Universidad de Zaragoza, Spain.

The influence of growth phase, cell concentration, pH and conductivity of treatment medium on the inactivation of Salmonella senftenberg by high electric field pulses (HELP) was studied. Cells were more resistant to HELP treatments at the beginning of the logarithmic phase and at the stationary phase. Microbial inactivation was not a function of the initial cell concentration. At constant input voltage, electric field strength obtained in the treatment chamber depended on medium conductivity. At the same electric field strength, conductivity did not influence S. senftenberg inactivation. At the same conductivity, inactivation of S. senftenberg was bigger at neutral than acidic pH.

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J Food Prot. 2003 Jun;66(6):1007-12.

Weibull distribution function based on an empirical mathematical model for inactivation of Escherichia coli by pulsed electric fields.

Rodrigo D, Barbosa-Cánovas GV, Martínez A, Rodrigo M.

Instituto de Agroquímica y Tecnología de Alimentos, Consejo Superior de Investigaciones Científicas, Apartado de Correos 73, 46100 Burjassot, Valencia, Spain.

The pulsed electric field inactivation kinetics of Escherichia coli suspended in orange juices with three different concentrations of carrot juice (0, 20, and 60%) was studied. Electric field strengths ranged from 25 to 40 kV/cm, and treatment times ranged from 40 to 340 micros. Experimental data were fitted to Bigelow, Hülsheger, and Weibull distribution functions, and the Weibull function provided the best fit (with the lowest mean square error). The dependency of each model's kinetic constant on electric field strength and carrot juice concentration was studied. A secondary model was developed to describe the relationship of Weibull parameters a and n to electric field strength and carrot juice concentration. An empirical mathematical model based on the Weibull distribution function, relating the natural logarithm of the survival fraction to treatment time, electric field strength, and carrot juice concentration, was developed. Parameters were estimated by a nonlinear regression. The results of this study indicate that the error rate for the model's predictions was 6.5% and that the model was suitable for describing E. coli inactivation.

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Appl Environ Microbiol. 1999 Dec;65(12):5364-71.

Effects of pulsed electric fields on inactivation kinetics of Listeria innocua.

Wouters PC, Dutreux N, Smelt JP, Lelieveld HL.

Microbiology & Preservation, Unilever Research Vlaardingen, 3133 AT Vlaardingen, The Netherlands. Patrick.Wouters@Unilever.com

The effects of pulsed electric field (PEF) treatment and processing factors on the inactivation kinetics of Listeria innocua NCTC 11289 were investigated by using a pilot plant PEF unit with a flow rate of 200 liters/h. The electric field strength, pulse length, number of pulses, and inlet temperature were the most significant process factors influencing the inactivation kinetics. Product factors (pH and conductivity) also influenced the inactivation kinetics. In phosphate buffer at pH 4.0 and 0.5 S/m at 40 degrees C, a 3. 0-V/microm PEF treatment at an inlet temperature of 40 degrees C resulted in > or = 6.3 log inactivation of strain NCTC 11289 at 49.5 degrees C. A synergistic effect between temperature and PEF inactivation was also observed. The inactivation obtained with PEF was compared to the inactivation obtained with heat. We found that heat inactivation was less effective than PEF inactivation under similar time and temperature conditions. L. innocua cells which were incubated for a prolonged time in the stationary phase were more resistant to the PEF treatment, indicating that the physiological state of the microorganism plays a role in inactivation by PEF. Sublethal injury of cells was observed after PEF treatment, and the injury was more severe when the level of treatment was increased. Overall, our results indicate that it may be possible to use PEF in future applications in order to produce safe products.

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J Food Prot. 1998 Sep;61(9):1203-6.

Inactivation of Listeria monocytogenes in milk by pulsed electric field.

Reina LD, Jin ZT, Zhang QH, Yousef AE.

Department of Food Science and Technology, Ohio State University, Columbus 43210, USA.

Pasteurized whole, 2%, and skim milk were inoculated with Listeria monocytogenes Scott A and treated with high-voltage pulsed electric field (PEF). The effects of milk composition (fat content) and PEF parameters (electric field strength, treatment time, and treatment temperature) on the inactivation of the bacterium were studied. No significant differences were observed in the inactivation of L. monocytogenes Scott A in three types of milk by PEF treatment. With treatment at 25 degrees C, 1- to 3-log reductions of L. monocytogenes were observed. PEF lethal effect was a function of field strength and treatment time. Higher field strength or longer treatment time resulted in a greater reduction of viable cells. A 4-log reduction of the bacterium was obtained by increasing the treatment temperature to 50 degrees C. Results indicate that the use of a high-voltage PEF is a promising technology for inactivation of foodborne pathogens.

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Biotechnol Bioeng. 1992 Dec 20;40(11):1412-20.

Kinetics of sterilization of Lactobacillus brevis cells by the application of high voltage pulses.

Jayaram S, Castle GS, Margaritis A.

Department of Electrical Engineering, University of Western Ontario, London, Ontario, Canada N6A 5B9.

The technique of irreversible electroporation has been successfully applied to cause a lethal effect on Lactobacillus brevis cells suspended in phosphate buffer solution, Na(2)HPO(4)/NaH(2)PO(4) . H(2)O (0.845/0.186 mM) between parallel plane electrodes. Tests were carried out at different temperatures (24,45,60, and 80 degrees C) to determine if there was a synergistic effect of temperature and electric pulse treatment on the destruction of L. brevis. Experimental results indicate that the viability (log N/N(0); where N(0) and N are the number of cells survived per milliliter before and after pulse voltage application, respectively) of L. brevis decreased with electric field strength E and temperature T and treatment time t(t). The relations between log(N/N(0)) and t(t) and log(N/N(0)) and E indicate that higher field strengths are more effective than higher treatment times in causing destruction of L. brevis cells. It was also found that as the temperature of the liquid medium containing L. brevis cells increased from 24 to 60 degrees C, the death rate of L. brevis cells increased with a decrease in the total treatment time t(t) (pulse width x number of pulses applied). The application of an electric field strength E = 25 kV/cm at 60 degrees C and treatment time t(t) = 10 ms resulted in very high destruction levels of L. brevis cells (N/N(0) = 10(-9)). In comparison with existing steam sterilization technology, this new method of sterilization using relatively low temperature and short treatment time could prove to be an excellent method to minimize thermal denaturation of important nutrient components in liquid media. (c) John Wiley & Sons, Inc.

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Int J Food Microbiol. 2004 May 15;93(1):1-10.

Growth of pulsed electric field exposed Escherichia coli in relation to inactivation and environmental factors.

Aronsson K, Borch E, Stenlöf B, Rönner U.

SIK, The Swedish Institute for Food and Biotechnology, Box 5401, 402 29 Göteborg, Sweden.

Pulsed electric fields (PEF) have been proven to inactivate microorganisms during nonthermal conditions and have the potential to replace thermal processing as a method for food preservation. However, there is a need to understand the recovery and growth of survivors and potentially injured microorganisms following PEF processing. The purpose of this investigation was to study the growth of Escherichia coli at 10 degrees C following exposure to electrical field strengths (15, 22.5 and 30 kV/cm) in relation to inactivation and the amount of potentially sublethally injured cells. One medium was used as both a treatment medium and an incubation medium, to study the influence of environmental factors on the inactivation and the growth of the surviving population. The pH (5.0, 6.0 and 7.0) and water activity (1.00, 0.985 and 0.97) of the medium was varied by adding HCl and glycerol, respectively. Growth was followed continuously by measuring the optical density. The time-to-detection (td) and the maximum specific growth rate (micromax) were calculated from these data. Results showed that the PEF process did not cause any obvious sublethal injury to the E. coli cells. The number of survivors was a consequence of the combination of electrical field strength and environmental factors, with pH being the most prominent. Interestingly, the micromax of subsequent growth was influenced by the applied electrical field strength during the process, with an increased micromax at more intense electrical field strengths. In addition, the micromax was also influenced by the pH and water activity. The td, which could theoretically be considered as an increase in shelf life, was found to depend on a complex correlation between electrical field strength, pH and water activity. That could be explained by the fact that the td is a combination of the number of survivors, the recovery of sublethal injured cells and the growth rate of the survivors. Copyright 2003 Elsevier B.V.

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J Appl Microbiol. 2005;99(1):94-104.

Occurrence of sublethal injury after pulsed electric fields depending on the micro-organism, the treatment medium ph and the intensity of the treatment investigated.

García D, Gómez N, Mañas P, Condón S, Raso J, Pagán R.

Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Universidad de Zaragoza, Zaragoza, Spain.

AIMS: The objective was to investigate the occurrence of sublethal injury after pulsed electric field (PEF) depending on the treatment time, the electric field strength and the pH of the treatment media in two Gram-positive (Bacillus subtilis ssp. niger, Listeria monocytogenes) and six Gram-negative (Escherichia coli, Escherichia coli O157:H7, Pseudomonas aeruginosa, Salmonella serotype Senftenberg 775W, Salmonella serotype Typhimurium, Yersinia enterocolitica) bacterial strains. METHODS AND RESULTS: A characteristic behaviour was observed for the Gram-positive and Gram-negative bacteria studied. Whereas Gram-positive bacteria showed a higher PEF resistance at pH 7.0, the Gram-negative were more resistant at pH 4.0. In these conditions, in which bacteria showed their maximum resistance, a large proportion of sublethally injured cells were detected. In most cases, the longer the treatment time and the higher the electric field applied, the greater the proportion of sublethally injured cells that were detected. No sublethal injury was detected when Gram-positive bacteria were treated at pH 4.0 and Gram-negative at pH 7.0. CONCLUSIONS: Sublethal injury was detected after PEF so, bacterial inactivation by PEF is not an 'all or nothing' event. SIGNIFICANCE AND IMPACT OF THE STUDY: This work could be useful for improving food preservation by PEF.

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Biochim Biophys Acta. 1996 Jan 12;1278(1):79-88.

Contribution to the biophysics of the lethal effects of electric field on microorganisms.

Kekez MM, Savic P, Johnson BF.

National Research Council of Canada, Ottawa, Canada.

The proposed model assumes that the criteria leading to the lethal breakdown of microorganisms suspended in a continuous medium depend on two parameters: (a) the applied electric field must exceed the critical field of membrane to create holes and (b) the Joule energy (deposited in the membrane) must exceed the minimum value beyond which the cell can not recover. The first parameter initiates (reversible) breakdown and the second one, the completion of the (irreversible) electrical breakdown leading to death of the cell. The number of cells surviving the electric field treatment is related to statistical distribution of cell size. Comparison between theory and the experimental results of Kinosita and Tsong (1977); Hülsheger et al. (1980, 1981, 1983); Rosemberg and Korenstein (1990) and others is given.
PMID: 8611611 [PubMed - indexed for MEDLINE]

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J Water Health. 2004 Dec;2(4):267-77.

The effectiveness of a multi-spark electric discharge system in the destruction of microorganisms in domestic and industrial wastewaters.

Anpilov AM, Barkhudarov EM, Christofi N, Kop'ev VA, Kossyi IA, Taktakishvili MI, Zadiraka YV.

General Physics Institute of the Russian Academy of Sciences, 38 Vavilov Street, Moscow, Russia.

The aim of this work was to investigate the effectiveness of a high voltage multi-spark electric discharge, with pulse energy of 1 Joule, in killing microorganisms in wastewater. Wastewater from primary treated effluent arising from domestic and industrial sources was abstracted for continuous pulsed discharge disinfection. The wastewater contained a large mixed population of microorganisms (approximately 10(7) CFU ml(-1) [10(9) CFU 100 ml(-1)] total aerobic heterotrophic bacteria) including vegetative cells and spores. The electrical conductivity of the wastewater ranged from 900-1400 microS cm(-1) and it was shown that a specific energy of 1.25-1.5 J cm(-3) was required to achieve 1 log reduction in bacterial (faecal coliforms/total aerobic heterotrophs) content. This is higher than that previously shown to reduce the population of E. coli in tap water of low conductivity, demonstrating the role of total wastewater constituents, including dissolved and particulate substances, water colour and the presence of microbial spores, in effective disinfection. The system can be engineered to eradicate microbial populations to levels governed by legislation by increasing treatment time or energy input.

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J Food Prot. 1999 Dec;62(12):1381-6.

High intensity pulsed electric fields applied to egg white: effect on Salmonella Enteritidis inactivation and protein denaturation.

Jeantet R, Baron F, Nau F, Roignant M, Brulé G.

Laboratoire de Technologie Alimentaire, Ecole Nationale Supérieure Agronomique, Rennes, France. jeantet@agrorennes.educagri.fr

High-intensity electric fields have been successfully applied to the destruction of Salmonella Enteritidis in diaultrafiltered egg white. The effects of electric field strength (from 20 to 35 kV x cm(-1)), pulse frequency (from 100 to 900 Hz), pulse number (from 2 to 8), temperature (from 4 to 30 degrees C), pH (from 7 to 9), and inoculum size (from 10(3) to 10(7) CFU x ml(-1)) were tested through a multifactorial experimental design. Experimental results indicate that, for Salmonella inactivation, the electric field intensity is the dominant factor with a strongly positive effect, strengthened by its positive interaction with pulse number. Pulse number, temperature, and pH have also significant positive effects but to a lesser extent. In the most efficient conditions, the pulsed electric field (PEF) treatment is capable of 3.5 log10 reduction in viable salmonellae. Simultaneously, the measure of surface hydrophobicity does not indicate any increase after PEF treatment. These results suggest that no protein denaturation occurs, unlike what is observed after comparable heat treatment in terms of Salmonella inactivation (55 degrees C for 15 min).

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Antimicrob Agents Chemother. 1994 Dec;38(12):2803-9.

Mechanism of electrical enhancement of efficacy of antibiotics in killing biofilm bacteria.

Costerton JW, Ellis B, Lam K, Johnson F, Khoury AE.

Center for Biofilm Engineering Montana State University, Bozeman. 59717-0398.

The bioelectric effect, in which electric fields are used to enhance the efficacy of biocides and antibiotics in killing biofilm bacteria, has been shown to reduce the very high concentrations of these antibacterial agents needed to kill biofilm bacteria to levels very close to those needed to kill planktonic (floating) bacteria of the same species. In this report, we show that biofilm bacteria are readily killed by an antibiotic on all areas of the active electrodes and on the surfaces of conductive elements that lie within the electric field but do not themselves function as electrodes. Considerations of electrode geometry indicate that very low (< 100 microA/cm2) current densities may be effective in this electrical enhancement of antibiotic efficacy against biofilm bacteria, and flow experiments indicate that this bioelectric effect does not appear to depend entirely on the possible local electrochemical generation of antibacterial molecules or ions. These data are expected to facilitate the use of the bioelectric effect in the prevention and treatment of device-related bacterial infections that are caused by bacteria that grow in biofilms and thereby frustrate antibiotic chemotherapy.

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Antimicrob Agents Chemother. 2004 Dec;48(12):4662-4.

A radio frequency electric current enhances antibiotic efficacy against bacterial biofilms.

Caubet R, Pedarros-Caubet F, Chu M, Freye E, de Belém Rodrigues M, Moreau JM, Ellison WJ.

Unité Sécurité Microbiologique des Aliments, Institut des Sciences et Techniques des Aliments de Bordeaux, Université de Bordeaux 1, Talence, France. r.caubet@istab.u-bordeaux1.fr

Bacterial biofilms are notably resistant to antibiotic prophylaxis. The concentration of antibiotic necessary to significantly reduce the number of bacteria in the biofilm matrix can be several hundred times the MIC for the same bacteria in a planktonic phase. It has been observed that the addition of a weak continuous direct electric current to the liquid surrounding the biofilm can dramatically increase the efficacy of the antibiotic. This phenomenon, known as the bioelectric effect, has only been partially elucidated, and it is not certain that the electrical parameters are optimal. We confirm here the bioelectric effect for Escherichia coli biofilms treated with gentamicin and with oxytetracycline, and we report a new bioelectric effect with a radio frequency alternating electric current (10 MHz) instead of the usual direct current. None of the proposed explanations (transport of ions within the biofilm, production of additional biocides by electrolysis, etc.) of the direct current bioelectric effect are applicable to the radio frequency bioelectric effect. We suggest that this new phenomenon may be due to a specific action of the radio frequency electromagnetic field upon the polar parts of the molecules forming the biofilm matrix.

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Lab Chip. 2005 Sep;5(9):943-8. Epub 2005 Jul 26.

A new pulsed electric field microreactor: comparison between the laboratory and microtechnology scale.

Fox M, Esveld E, Luttge R, Boom R.

Food and Bioprocess Engineering Group, Wageningen University, P.O. Box 8129, 6700 EV, Wageningen, The Netherlands. Martijn.Fox@wur.nl

This paper presents a new microreactor dedicated for pulsed electric field treatment (PEF), which is a pasteurization method that inactivates microorganisms with short electric pulses. The PEF microreactor consists of a flow-through channel with a constriction where the electric field is focussed. Compared to a laboratory-scale setup 25 times lower voltages were needed to obtain the same electric field strength due to the close electrode spacing. A finite element model showed that the electric field intensity is very homogeneous throughout the channel, which is crucial for the pasteurization processes. Experiments where artificial vesicles, loaded with carboxyfluorescein, were electroporated showed that the maximum transmembrane potential adequately described the processes both in the microreactor and the laboratory-scale setup, although the length scales are different. Electroporation started at a transmembrane potential of 0.5 V, reaching a maximum fraction of electroporated vesicles of 51% at a transmembrane potential of 1.5 V. The partial electroporation is not a result of the heterogenity of the vesicles or the electric field. With this new PEF microreactor it is possible to study the PEF process in more detail.

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Anticancer Res. 2001 May-Jun;21(3B):1809-15.

A new antitumour treatment combining radiation and electric pulses.

Engström PE, Persson BR, Brun A, Salford LG.

Department of Radiation Physics, Lund University Hospital, Sweden.

AIM: To investigate the antitumour effect of radiation in combination with electropermeabilization on subcutaneous rat glioma tumours. MATERIALS AND METHODS: Sub-optimal radiation treatment was administered separately or in combination with electric pulses of high voltage to subcutaneous rat brain tumours. The treatment was repeated on four consecutive days and evaluated by TGD and microscopical examination. The tumours were stained for Factor VlII/von Willebrand Factor to investigate the effects on the tumour vasculature. RESULTS: Radiation and electric pulses applied concomitantly resulted in a cure rate of 67% (tumour free >80 days after treatment). Radiation-treated animals showed progressive disease. Histological and immunohistochemical examination of electric impulse-treated tumours showed instant and severe deteriorating effects on tumour vasculature. CONCLUSION: A distinct antitumour effect of the combined treatment of electric pulses and radiation treatment was observed. We believe that the tumouricidal effect arises from destruction of the tumour vasculature but also from DNA related damage from reactive oxygen formed by the electric pulses and the radiation treatment.

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Int J Food Microbiol. 2003 Oct 15;87(1-2):87-95.

The influence of process parameters for the inactivation of Listeria monocytogenes by pulsed electric fields.

Alvarez I, Pagán R, Condón S, Raso J.

Tecnología de los Alimentos, Facultad de Veterinaria, Universidad de Zaragoza, 50.013 Saragossa, Spain.

The influence of the electric field strength, the treatment time, the total specific energy and the conductivity of the treatment medium on the Listeria monocytogenes inactivation by pulsed electric fields (PEF) has been investigated. L. monocytogenes inactivation increased with the field strength, treatment time and specific energy. A maximum inactivation of 4.77 log(10) cycles was observed after a treatment of 28 kV/cm, 2000 micros and 3490 kJ/kg. The lethal effect of PEF treatments on L. monocytogenes was not influenced by the conductivity of the treatment medium in a range of 2, 3 and 4 mS/cm when the total specific energy was used as a PEF control parameter. A mathematical model based on the Weibull distribution was fitted to the experimental data when the field strength (15-28 kV/cm), treatment time (0-2000 micros) and specific energy (0-3490 kJ/kg) were used as PEF control parameters. A linear relationship was obtained between the log(10) of the scale factor (b) and the electric field strength when the treatment time and the total specific energy were used to control the process. The total specific energy, in addition to the electric field strength and the treatment time, should be reported in order to evaluate the microbial inactivation by PEF.

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Water Res. 2002 Aug;36(14):3429-38.

Elimination of free-living amoebae in fresh water with pulsed electric fields.

Vernhes MC, Benichou A, Pernin P, Cabanes PA, Teissié J.

Institut de Pharmacologic et de Biologie Structurale, CNRS UMR 5089, Toulouse, France.

This study investigates the effects of pulsed electric fields on the inactivation of trophozoite form of Naegleria lovaniensis Ar9M-1 in batch and flow processes, systematically examining the lethal effect of field strength, pulse duration, number of pulses, and pulse frequency. Our results show that amoebae eradication is modulated by pulse parameters, composition of the pulsing medium, and physiological state of the cells. Cell survival is not related to the energy delivered to the cell suspension during the electrical treatment. For a given energy a strong field applied for a short cumulative pulse duration affects viability more than a weak field with a long cumulative pulsation. We also determine the optimal electrical conditions to obtain an inactivation rate higher than 95% while using the least energy. Flow processes allow to treat large-scale volumes. Our results show that the most efficient flow process for amoeba eradication requires a field parallel to the flow. Pulsed electric fields are a new and attractive method for inactivating amoebae in large volumes of fresh water.

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J Dairy Sci. 2006 Mar;89(3):905-11.

Comparative study on shelf life of whole milk processed by high-intensity pulsed electric field or heat treatment.

Odriozola-Serrano I, Bendicho-Porta S, Martín-Belloso O.

Department of Food Technology UTPV-CeRTA, University of Lleida Rovira Roure 191, 25198 Lleida, Spain.

The effect of high-intensity pulsed electric fields (HI-PEF) processing (35.5 kV/cm for 1,000 or 300 micros with bipolar 7-micros pulses at 111 Hz; the temperature outside the chamber was always < 40 degrees C) on microbial shelf life and quality-related parameters of whole milk were investigated and compared with traditional heat pasteurization (75 degrees C for 15 s), and to raw milk during storage at 4 degrees C. A HIPEF treatment of 1,000 micros ensured the microbiological stability of whole milk stored for 5 d under refrigeration. Initial acidity values, pH, and free fatty acid content were not affected by the treatments; and no proteolysis and lipolysis were observed during 1 wk of storage in milk treated by HIPEF for 1,000 micros. The whey proteins (serum albumin, beta-lactoglobulin, and alpha-lactalbumin) in HIPEF-treated milk were retained at 75.5, 79.9, and 60%, respectively, similar to values for milk treated by traditional heat pasteurization.

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Lett Appl Microbiol. 2002;35(1):90-4.

Pulsed high voltage electric discharge disinfection of microbially contaminated liquids.

Anpilov AM, Barkhudarov EM, Christofi N, Kop'ev VA, Kossyi IA, Taktakishvili MI, Zadiraka Y.

General Physics Institute, Moscow, Russia.

AIMS: To examine the use of a novel multielectrode slipping surface discharge (SSD) treatment system, capable of pulsed plasma discharge directly in water, in killing micro-organisms. METHODS AND RESULTS: Potable water containing Escherichia coli and somatic coliphages was treated with pulsed electric discharges generated by the SSD. The SSD system was highly efficient in the microbial disinfection of water with a low energy utilization (eta approximately 10-4 kW h l-1). CONCLUSIONS: The SSD treatment was effective in the destruction of E. coli and its coliphages through the generation of u.v. radiation, ozone and free radicals. SIGNIFICANCE AND IMPACT OF THE STUDY: The non-thermal treatment method can be used for the eradication of micro-organisms in a range of contaminated liquids, including milk, negating the use of pasteurization. The method utilizes multipoint electric discharges capable of treating large volumes of liquid under static and flowing regimes.

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Anal Bioanal Chem. 2004 Nov;380(5-6):831-7.

Simultaneous determination of multiple constituents in real beer samples of different origins by capillary zone electrophoresis.

Cortacero-Ramírez S, Segura-Carretero A, Cruces-Blanco C, Romero-Romero ML, Fernández-Gutiérrez A.

Research Laboratories of Grupo Cervezas Alhambra, S.L. Avda. Murcia 1, 18010 Granada, Spain.

Simultaneous determination of alcohols, amines, amino acids, flavonoids, and purine and pyrimidine bases in bottled beer samples directly without any pre-treatment was carried out by capillary zone electrophoresis with diode-array detection. Electrolyte conditions such as pH, composition and concentration of the buffer, working voltage and type and time of injection were checked. The best separation of the cited analytes was achieved in 70 mM sodium borate solution and pH 10.25. The detection limits were from 2.1 to 5.6 mg L(-1) for the 18 compounds studied. The developed method is rapid, sensitive and quantitative and has been applied to seven types of international bottled beers of different origins bought locally.

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Endod Dent Traumatol. 1985 Jun;1(3):112-5.

Effect of electric current and silver electrodes on oral bacteria.

Tronstad L, Trope M, Hammond BF.

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Zhongguo Zhong Yao Za Zhi. 1992 Oct;17(10):604-6, 639.

Research on sterilization of pathogens by high electrostatic voltage method

Wang X, Wu Y, Ni X, Xia B, Xu J, Du Q.

Institute of Electrostatics, Northeast Normal University, Changchun.

An experimental research has been carried out on the sterilization of four kinds of pathogens by high electrostatic method along with an inquiry into the influence of voltage waveform and the treated time on sterilization. It is concluded that pathogens can be killed efficiently by corona discharge field.

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http://www.ncbi.nlm.nih.gov/pubmed/9151574 

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http://www.ncbi.nlm.nih.gov/pubmed/11588820?dopt=Abstract