La décontamination bactérienne de l'eau par impulsions électriques ultracourtes

Using various prototype of nanosecond pulsed electric field (nsPEF), eradication of microorganisms that are pathogens in industrial and domestic water was investigated. This matter becomes a societal issue since new European administrative constraints are coming out such as the legislation named REACH and the biocide directive. This legislation tries to limit the use of chemicals able to eradicate microorganisms. One of the different ways to eliminate micro-organisms such as bacteria consists in the delivery of pulsed electric fields (PEF). Nanosecond pulsed electric field (nsPEF) may be an interesting alternative with a lower energy cost when compared with ms or μs PEF technologies. However, only few insights are available that report a gain in cost and in efficiency as well. The aim of this study is to show that a strong decontamination in a reservoir can be obtained by using a derivated flow. A mathematical model (algorithm), using a language C program was developed to predict the effectiveness of the flow decontamination through a bypass. The work carried out has been to compare this theoretical model with laboratory tests. Efficiency and speediness of bacteria destruction was drastically improved and energy cost reduced thanks to optimization of flow parameter and improvement of generator performance.Les effets des champs électriques pulsés (CEP) sur les microorganismes ont été montrés depuis Sale et Hamilton. L'une des premières applications en a été l'électroporation cellulaire pour permettre la transfection de plasmides à travers la membrane plasmique. Il s'agit de la principale méthode de transfert de gènes. Un autre champ d'application est la décontamination de nourriture liquide. Mais la technologie capable de donner ces résultats en termes de décontamination requièrt, pour un champ électrique de faible amplitude, l'utilisation d'impulsions de longues durées provoquant une grande consommation énergétique. Ceci a été montré pour la décontamination du lait, des jus de fruits et du vin. Le mécanisme par lequel les CEP avec une durée milliseconde (ms) ou microseconde (µs) agissent est bien décrit et intervient sur la bicouche lipidique. Le but de cette thèse est d'étudier les possibilités d'utilisation des champs électriques pulsés nanosecondes (nsCEP) pour décontaminer de l'eau de procédés industriels. Un générateur d'impulsions haute tension associé à un applicateur constitué de deux électrodes planes permettent de générer un champ électrique homogène dans l'eau. Ce dispositif a d'abord été éprouvé en batch puis en flux sur des suspensions bactériennes (Escherichia coli BL21(DE3) et Legionella pneumophila sérogroupe 1) cultivées en laboratoire. L'utilisation de générateurs de plus en plus performants et l'optimisation des conditions de flux ont permis d'améliorer drastiquement le rendement énergétique de décontamination et la vitesse globale de traitement. Il a également été montré qu'il est possible de déterminer par le calcul, la vitesse de décontamination d'un tel système, à partir des caractéristiques des générateurs et des paramètres de fluidiques. Si ce travail n'a pas permis la réalisation d'un prototype d'échelle industrielle, les grandes lignes permettant le passage du procédé de l'échelle laboratoire à l'échelle industrielle ont été données

Pulsed Power Applications for Protein Conformational Change and the Permeabilization of Agricultural Products

Pulsed electric fields (PEFs), which are generated by pulsed power technologies, are being tested for their applicability in food processing through protein conformational change and the poration of cell membranes. In this article, enzyme activity change and the permeabilization of agricultural products using pulsed power technologies are reviewed as novel, nonthermal food processes. Compact pulsed power systems have been developed with repetitive operation and moderate output power for application in food processing. Firstly, the compact pulsed power systems for the enzyme activity change and permeabilization are outlined. Exposure to electric fields affects hydrogen bonds in the secondary and tertiary structures of proteins; as a result, the protein conformation is induced to be changed. The conformational change induces an activity change in enzymes such as α-amylase and peroxidase. Secondly, the conformational change in proteins and the induced protein functional change are reviewed. The permeabilization of agricultural products is caused through the poration of cell membranes by applying PEFs produced by pulsed discharges. The permeabilization of cell membranes can be used for the extraction of nutrients and health-promoting agents such as polyphenols and vitamins. The electrical poration can also be used as a pre-treatment for food drying and blanching processes. Finally, the permeabilization of cell membranes and its applications in food processing are reviewed

Growth Properties and Sensitivities to Various Bactericidal Methods of Cold-Tolerant Microorganisms Isolated from Packed Tofu

Disinfection and sterilization against cold-tolerant microorganisms are very important for enhancing food safety and hygiene management under refrigeration conditions. We isolated Exiguobacterium sp. and Pantoea sp. from an immersion solution of packed tofu and evaluated their growth properties and sensitivities to various bactericidal methods. These microorganisms were classified as psychrotrophic bacteria, according to their ability to grow at 4 °C, with an optimum growth temperature of 30 °C. Exiguobacterium sp. and Pantoea sp. were more sensitive to heat and sodium hypochlorite than Escherichia coli (E. coli). Exiguobacterium sp. was sensitive to acetic acid and citric acid, while Pantoea sp. was relatively insensitive and E. coli was insensitive to these organic acids. All microorganisms used in this study were resistant to sodium hydroxide solution (pH 8.00). Exiguobacterium sp. showed resistance to ozonated water and UV; therefore, particular attention should be paid to the contamination of this microorganism in food factories. Both Exiguobacterium sp. and Pantoea sp. were inactivated by pulsed electric field (PEF) treatment that did not cause lethal damage to E. coli. The results obtained in this study suggest that the bactericidal methods targeting the fragile cell membrane with high permeability are effective for the inactivation of cold-tolerant microorganisms

Growth Properties and Sensitivities to Various Bactericidal Methods of Cold-Tolerant Microorganisms Isolated from Packed Tofu

Disinfection and sterilization against cold-tolerant microorganisms are very important for enhancing food safety and hygiene management under refrigeration conditions. We isolated Exiguobacterium sp. and Pantoea sp. from an immersion solution of packed tofu and evaluated their growth properties and sensitivities to various bactericidal methods. These microorganisms were classified as psychrotrophic bacteria, according to their ability to grow at 4 °C, with an optimum growth temperature of 30 °C. Exiguobacterium sp. and Pantoea sp. were more sensitive to heat and sodium hypochlorite than Escherichia coli (E. coli). Exiguobacterium sp. was sensitive to acetic acid and citric acid, while Pantoea sp. was relatively insensitive and E. coli was insensitive to these organic acids. All microorganisms used in this study were resistant to sodium hydroxide solution (pH 8.00). Exiguobacterium sp. showed resistance to ozonated water and UV; therefore, particular attention should be paid to the contamination of this microorganism in food factories. Both Exiguobacterium sp. and Pantoea sp. were inactivated by pulsed electric field (PEF) treatment that did not cause lethal damage to E. coli. The results obtained in this study suggest that the bactericidal methods targeting the fragile cell membrane with high permeability are effective for the inactivation of cold-tolerant microorganisms