Electroporation is a method of treatment of plant tissue that due to its nonthermal nature enables preservation of the natural quality, colour and vitamin composition of food products. The range of processes where electroporation was shown to preserve quality, increase extract yield or optimize energy input into the process is overwhelming, though not exhausted; e.g. extraction of valuable compounds and juices, dehydration, cryopreservation, etc. Electroporation is—due to its antimicrobial action—a subject of research as one stage of the pasteurization or sterilization process, as well as a method of plant metabolism stimulation. This paper provides an overview of electroporation as applied to plant materials and electroporation applications in food processing, a quick summary of the basic technical aspects on the topic, and a brief discussion on perspectives for future research and development in the field. The paper is a review in the very broadest sense of the word, written with the purpose of orienting the interested newcomer to the field of electroporation applications in food technology towards the pertinent, highly relevant and more in-depth literature from the respective subdomains of electroporation research.

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Electroporation in Food Processing and Biorefinery

Chitosan is a naturally originating product that can be applied in many areas due to its biocompatibility, biodegradability, and nontoxic properties. The broad-spectrum antimicrobial activity of chitosan offers great commercial potential for this product. Nevertheless, the antimicrobial activity of chitosan varies, because this activity is associated with its physicochemical characteristics and depends on the type of microorganism. In this review article, the fundamental properties, modes of antimicrobial action, and antimicrobial effects-related factors of chitosan are discussed. We further summarize how microorganisms genetically respond to chitosan. Finally, applications of chitosan-based biomaterials, such as nanoparticles and films, in combination with current clinical antibiotics or antifungal drugs, are also addressed.

Antimicrobial Actions and Applications of Chitosan

The study was aimed at investigation of the potential of pulsed electric field (PEF) pre-treatment as a preliminary step of pH-assisted aqueous extraction of algae components from microalgae Nannochloropsis suspensions. The PEF and sonication (S) were compared as pretreatment methods. They were applied at normal (pH = 8.5) and basic (pH = 11) conditions, and supplementary basic extraction (at pH = 11) was done. The extracts were analyzed for content of pigments, proteins, carbohydrates, total phenolic compounds and antioxidant capacity. The colloidal stability of PEF- and S-pretreated suspensions was also evaluated. The data evidence that PEF technique allows selective extraction of a portion of pure proteins that are different from proteins extracted from S-pretreated suspensions. The discovered effects have shown the advantages of PEF-pretreatment at normal conditions (pH = 8.5) and supplementary extraction at basic conditions (pH = 11) for selective extraction of different intracellular components.

Pulsed electric field and pH assisted selective extraction of intracellular components from microalgae Nannochloropsis

The title of the Colloquium on Membranes, Ions, and Impulses was chosen from Cole’s book, and it is a pleasure to dedicate this collection of papers given at the Colloquium to Kacy. It is a privilege to be in the unique position of having been associated with both Kacy Cole and Dan Tosteson, our American Physiological Society President for 1974.

Membranes, ions, and impulses: Dedication to Kacy Cole

In vitro electroporation detection methods - An overview.

Magnetic diffusion is of great importance in the domain of electromechanical energy conversion since it can be a performance-limiting mechanism. This paper deals with magnetic diffusion in the case of the rails of a railgun. The experiments benefit from the use of a new type of high magnetic-field sensor based on thin ( < 1 mum) manganite films, which exhibits a colossal magnetoresistance (CMR) effect and has very small sensitive areas (e.g., 0.5 mm times 50 mum). Some basics about CMR and the design of the sensor are given. Several sensors were used and calibrated in the course of static transient railgun experiments. Here, varying spatial field distributions due to the use of different rail materials were recorded. Magnetic-field measurements during railgun operation with projectile velocities exceeding 1000 m/s have been successfully performed. By comparison with 3-D finite-element calculations, interesting results concerning magnetic diffusion have been worked out.

Magnetic Diffusion in Railguns: Measurements Using CMR-Based Sensors

The accurate measurement of the magnetic field distribution during electromagnetic launch experiments is an ambitious task. Loop sensors are widely used for detecting the change in magnetic flux. However, this technique is mostly used only for qualitative purposes, e.g., for triggering various devices. This paper deals with the use of another type of high magnetic field sensor based on thin (<1 mum) manganite films, which exhibit the colossal magnetoresistance (CMR) effect. This sensor measures the magnitude of the magnetic induction and can have very small sensitive areas (e.g., 0.5 mmtimes50 mum). Some basics about CMR and the design of the sensor are given. Several sensors were used in experiments performed with the ISL-launcher EMA3 (Eprim =0.6 MJ, l=3 m, cal=15 mmtimes30 mm). Transient magnetic field profiles with rise times of approximately 50 mus and amplitudes up to 4 T were recorded. The results obtained with the CMR sensors are compared with those of conventional loop sensors. Also, some metrological peculiarities due to high-frequency coupling to the detector circuit are mentioned. The highly local measurements of these CMR sensors were validated by results obtained from 3-D finite element (FE) calculations of the magnetic field distributions

Highly Local Measurements of Strong Transient Magnetic Fields During Railgun Experiments Using CMR-Based Sensors

We present the design and the main characteristics of the CMR-B-scalar sensor based on polycrystalline La0.83Sr0.17MnO3 films. The sensor active volume is only 400 μm × 50 μm × 0.4 μm, and it is able to measure a magnetic induction of up to 40 T independently on its direction. The investigations of the influence of film preparation conditions on the sensitivity of the device to magnetic field amplitudes, its direction, and ambient temperature variations are presented and discussed. It is demonstrated that, for room temperature conditions, sensors based on films deposited on a lucalox substrate at a 700°C temperature are most suitable. They have a low anisotropy effect (7% at 0.5 T and 3% at higher fields) and significant magnetoresistance values (~30% at 10 T). The dynamics of a CMR response to pulsed magnetic fields is shown, and the operational speed of the sensor is discussed. Moreover, the investigations of electromotive forces induced by a "loop" effect in the bias current cable are presented. A practical solution to counter this effect is offered.

B-Scalar Sensor Using CMR Effect in Thin Polycrystalline Manganite Films

An investigation of the yeast cell resealing process was performed by studying the absorption of the tetraphenylphosphonium (TPP+) ion by the yeast Saccharomyces cerevisiae. It was shown that the main barrier for the uptake of such TPP+ ions is the cell wall. An increased rate of TPP+ absorption after treatment of such cells with a pulsed electric field (PEF) was observed only in intact cells, but not in spheroplasts. The investigation of the uptake of TPP+ in PEF treated cells exposed to TPP+ for different time intervals also showed the dependence of the absorption rate on the PEF strength. The modelling of the TPP+ uptake recovery has also shown that the characteristic decay time of the non-equilibrium (PEF induced) pores was approximately a few tens of seconds and this did not depend on the PEF strength. A further investigation of such cell membrane recovery process using a florescent SYTOX Green nucleic acid stain dye also showed that such membrane resealing takes place over a time that is like that occurring in the cell wall. It was thus concluded that the similar characteristic lifetimes of the non-equilibrium pores in the cell wall and membrane after exposure  to  PEF indicate a strong coupling between these parts of the cell.

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The link between yeast cell wall porosity and plasma membrane permeability after PEF treatment.

We present local measurements of absolute values of pulsed magnetic fields in a typical electromagnetic launching system-a small coilgun. For this purpose, we designed magnetic field sensors based on thin polycrystalline La0.83Sr0.17MnO3 films exhibiting a colossal magnetoresistance (CMR) effect. We measured the magnetic field distribution inside the bore of a coilgun consisting of a multilayer coil and inserted a copper projectile in the shape of a hollow cylinder using an array of CMR-based sensors. In order to identify places with highly inhomogeneous magnetic field changes in direction and value, we simulated a pulsed magnetic field inside the coilgun. The measurements of magnetic induction compared well with simulations. CMR-based sensors are able to measure highly inhomogeneous magnetic fields in very small areas independently of the magnetic field direction with respect to the orientation of the sensor.

Nerija Zurauskiene

Papers

Magnetic Diffusion in Railguns: Measurements Using CMR-Based Sensors

Highly Local Measurements of Strong Transient Magnetic Fields During Railgun Experiments Using CMR-Based Sensors

B-Scalar Sensor Using CMR Effect in Thin Polycrystalline Manganite Films

The link between yeast cell wall porosity and plasma membrane permeability after PEF treatment.

B-Scalar Measurements by CMR-Based Sensors of Highly Inhomogeneous Transient Magnetic Fields