High hydrostatic pressure (HHP), pulsed electric fields (PEFs), ultrasound (US), and cold plasma (CP) are emerging technologies that have already found application in the food industry or related sectors. This review aims to describe the basic principles of these nonthermal technologies as well as the state of the art concerning their impact on biological cells, enzymes, and food constituents. Current and potential applications will be discussed, focusing on process-structure-function relationships, as well as recent advances in the process development.

Emerging Technologies in Food Processing

In recent years, several publications on microfluidic devices have focused on the process of electroporation, which results in the poration of the biological cell membrane. The devices involved are designed for cell analysis, transfection or pasteurization. The high electric field strengths needed are induced by placing the electrodes in close proximity or by creating a constriction between the electrodes, which focuses the electric field. Detection is usually achieved through fluorescent labeling or by measuring impedance. So far, most of these devices have only concerned themselves solely with the electroporation process, but integration with separation and detection processes is expected in the near future. In particular, single-cell content analysis is expected to add further value to the concept of the microfluidic chip. Furthermore, if advanced pulse schemes are employed, such microdevices can also enhance research into intracellular electroporation.

Electroporation of cells in microfluidic devices: a review

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

The impact of pulsed electric fields (PEF) on phospholipid vesicles, plant and animal as well as microbial and protozoa membranes was investigated. A series of pulse modulators and treatment chambers was realized in order to examine the diversity of components, materials and processing parameters. Electric field strength, energy input and treatment temperature were identified as key processing parameters. A critical field strength of 0.3 to 0.5 kV/cm for plant and animal and 10 to 15 kV/cm for microbial cells was observed. Degree of permeabilization was investigated by impedance analysis for plant and animal tissue and flow cytometry for microbes and liposomes to optimize processing parameters. The impact of membrane permeabilization on mass transfer processes was investigated for plant and animal tissue in laband technical scale. It was shown that extractability of fruit and vegetable juices or intracellular compounds can be enhanced after a PEF-treatment. An increase of up to 7 % of yield was found in comparison to untreated samples, juice quality was equivalent. Technical-scale treatments revealed the impact of a PEF-treatment on structural properties of fruit mash, an adaptation of liquid-solid separation techniques was shown to be required. A PEF-treatment of meat resulted in enhanced mass transfer during drying as well as brining of products, an improvement of water binding during cooking was found due to improved microdiffusion of brine and water binding agents. Microbial inactivation was investigated in different liquid media. For fruit juice and milk the applicability to achieve a gentle preservation was shown. The impact of processing parameters was evaluated in order to reduce electric energy requirements. A combined application of PEF and mild heat showed highly synergetic effects and improved energy efficiency. Enzyme inactivation was determined for lactoperoxidase in milk in comparison to thermal inactivation. It was observed that only a minor part of the inactivation was related to electric field effects, whereas at higher treatment intensities mainly thermal effects occurred. In addition the PEF applicability to achieve disintegration of sludge during waste water processing and for preservation of algae extracts was shown. Energy requirements to induce pore formation in different biological membrane systems were compared dependent on transmembrane potential induced. An analysis of cost efficiency showed that disintegration of plant and animal material by PEF is superior in comparison to a conventional treatment in terms of energy and time requirements as well as costs of operation. For microbial inactivation by PEF even an optimized treatment resulted in higher production costs, but consumer and quality benefits might justify these extra efforts for premium or thermally sensitive products. Meat, fruit and vegetable treatment were identified as the most promising applications to achieve a broad industrial exploitation of the technique, approximately 50 years after first empirical reports by Heinz Doevenspeck. Acknowledgements III

https://depositonce.tu-berlin.de/bitstream/11303/1738/1/Dokument_49.pdf

Pulsed Electric Fields (PEF) for Permeabilization of Cell Membranes in Food- and Bioprocessing – Applications, Process and Equipment Design and Cost Analysis.

Fossil resources-free sustainable development can be achieved through a transition to bioeconomy, an economy based on sustainable biomass-derived food, feed, chemicals, materials, and fuels. However, the transition to bioeconomy requires development of new energy-efficient technologies and processes to manipulate biomass feed stocks and their conversion into useful products, a collective term for which is biorefinery. One of the technological platforms that will enable various pathways of biomass conversion is based on pulsed electric fields applications (PEF). Energy efficiency of PEF treatment is achieved by specific increase of cell membrane permeability, a phenomenon known as membrane electroporation. Here, we review the opportunities that PEF and electroporation provide for the development of sustainable biorefineries. We describe the use of PEF treatment in biomass engineering, drying, deconstruction, extraction of phytochemicals, improvement of fermentations, and biogas production. These applications show the potential of PEF and consequent membrane electroporation to enable the bioeconomy and sustainable development.

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Energy-efficient biomass processing with pulsed electric fields for bioeconomy and sustainable development

Liquid pumpable food is mostly pasteurised by heat treatment. In the last decennia there is an increasing interest in so-called Pulsed Electric Field (PEF) treatment. During this treatment food is pumped between two metal electrodes and exposed to short high electric field pulses, typical 2-4 kV mm-1 during 1-10 μs. During this treatment the stainless steel electrodes are in direct contact with the food product. Associated with the charge that has to be exchanged at the interface of electrode and food, electrode material may be transferred from electrode to food. This transfer of material may cause serious electrode corrosion and adds metals to the food. The magnitude of material transfer depends on many factors such as current magnitude, pulse duration, pulse shape and fluid constitution. In this contribution the effect of three different mono-polar pulse shapes on treatment chamber corrosion is investigated. Experiments are carried out in an aqueous sodium chloride solution. The experiments showed that due to PEF treatment dissolved metals are present in the liquid. The four main elements of stainless steel, iron, chromium, nickel and manganese, have been considered in particular. These elements could only be detected in the liquid when it was repeatedly exposed to a Pulsed Electric Field treatment, which was realised by repeatedly circulating. From the experiments a relationship between dissolved metals in sodium chloride and the transferred charge is derived. With these values an upper limit for dissolved metals caused by PEF treatment can be defined. © 2005 Elsevier Ltd. All rights reserved.

Metal release in a stainless steel Pulsed Electric Field (PEF) system: Part I. Effect of different pulse shapes; theory and experimental method

In the last decennia, there is an increasing interest in pulsed electric field (PEF) treatment. The product is often treated in a continuous flow treatment chamber with stainless steel electrodes and exposed to short pulsed electric fields, typically 2-4 kV mm-1 during 1-10 μs. Due to direct contact of the treatment chamber electrodes with the food product, the main elements of these stainless steel electrodes are able to dissolve in the treated product. The magnitude of the material transfer depends on many factors such as current magnitude, pulse duration, pulse shape, and product constitution. In this contribution, the effect of metal dissolving during a monopolar pulse shape, generated by a pulse forming network, is investigated. Experiments are carried out with single and repeated PEF treatments in orange juice. These experiments showed that, due to PEF treatment, dissolved metals are present in the juice. The four main elements of stainless steel, iron, chromium, nickel, and manganese, have been considered in particular. The metal concentrations found do not exceed the legislation values for fruit juices and the EU Drinking Water Directive [EU Drinking Water Directive, http://www.europe.eu.int/. for human consumption. From the experiments, a relationship between dissolved metals in orange juice and the transferred charge is derived. In addition, a lifetime prediction of the treatment chamber caused by release of metals has been made. © 2005 Elsevier Ltd. All rights reserved.

Metal release in a stainless steel pulsed electric field (PEF) system Part II. The treatment of orange juice; related to legislation and treatment chamber lifetime

Liquid pumpable food is mostly pasteurised by heat treatment. One of the new methods is an intense pulsed electric fields (PEF) treatment. The treated food is pumped between two metal electrodes and exposed to very short high voltage pulses, typically tens of kV during several microseconds. During this treatment the electrodes are in direct contact with the food product. The interfacial charge, which must be transferred between electrode and food, can cause serious electrode damage, depending on many factors such as current magnitude, pulse duration, pulse shape and fluid constitution. In this contribution three different topologies of a high-voltage pulse generator, resulting in three different pulse shapes, are compared in relation to treatment chamber corrosion. The experiments indicate that during repeated PEF treatment different dissolved metal concentrations are found in the liquid. The results are qualitatively clarified from theory. (4 pages)

H.E. Berg

Papers

Metal release in a stainless steel Pulsed Electric Field (PEF) system: Part I. Effect of different pulse shapes; theory and experimental method

Metal release in a stainless steel pulsed electric field (PEF) system Part II. The treatment of orange juice; related to legislation and treatment chamber lifetime

Corrosion experiments in a pulsed electric field (PEF) treatment chamber with stainless steel electrodes fed with three different pulse shapes