Recommendations guidelines on the key information to be reported in studies of application of PEF technology in food and biotechnological processes

Effect of Pulsed Electric Field (PEF) on Bacterial Viability and Whey Protein in the Processing of Raw Milk

There is growing concern regarding the nutritional value of processed food products. Although thermal pasteurization, used in food processing, is a safe method and is widely applied in the food industry, food products lack quality and nutritional value because of the high temperatures used during pasteurization. In this study, the effect of pulsed electric field (PEF) processing on whey protein content and bacterial viability in raw milk was evaluated by changing the PEF strength and number of pulses. For comparison, traditional pasteurization techniques, such as low-temperature long-time (LTLT), ultra-high temperature (UHT), and microfiltration (MF), were also tested for total whey protein content, bacterial activity, and coliforms. We found that, after treatment with PEF, a significant decrease in total bacterial viability of 2.43 log and coliforms of 0.9 log was achieved, although undenatured whey protein content was not affected at 4.98 mg/mL. While traditional pasteurization techniques showed total bacterial inactivation, they were detrimental for whey protein content: β-lactoglobulin was not detected using HPLC in samples treated with UHT. LTLT treatment led to a significant decrease of 75% in β-lactoglobulin concentration; β-lactoglobulin content in milk samples treated with MF was the lowest compared to LTLT and UHT pasteurization, and ~10% and 27% reduction was observed.

Microbial analysis and virulence genes detection of milk preserved using heat-assisted pulsed electric field

Objective

Microbial analysis in milk preserved using heat-assisted Pulsed Electric Field (PEF) need to be assessed. In this study we analyze the microbial quality and virulence-associated genes in milk samples preserved using heat-assisted PEF from several producers in Indonesia.

Results

Milk samples were collected consisting of raw milk, milks taken after the heating, PEF, mixing, cooling, and packaging. Microbiological and Polymerase Chain Reaction (PCR) detection for virulence genes were performed. Heat-assisted PEF treatment gave 2.7–7.47 log reduction for TPC; 1.6–2.56 log reduction for MPN number; 3.13–6.48 log reduction for S. aureus; and for B. cereus there was an increase of 0.76 log and a reduction of 0.46 log. While milk samples from thermal pasteurization gave log reduction numbers of TPC, MPN, and S. aureus respectively 5.28; 2.56; and 4.73, for B. cereus was increasing 2.4 log. Producer C performed the best results with significant reduction compared with others (p < 0.005). There were no colonies of L. monocytogenes found in all of the samples. PCR results showed that milk samples possessed virulence genes 17.5% (10/57) of invA genes, 54.4% (31/57) of nheA genes, 68.4% (39/57) of cytK genes, 38.6% (22/57) of nuc genes, 63.2% (36/57) of ileS genes, while hly and actA genes were not detected.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05805-3.

Emerging Green Techniques for the Extraction of Antioxidants from Agri-Food By-Products as Promising Ingredients for the Food Industry

Nowadays, the food industry is heavily involved in searching for green sources of valuable compounds, to be employed as potential food ingredients, to cater to the evolving consumers’ requirements for health-beneficial food ingredients. In this frame, agri-food by-products represent a low-cost source of natural bioactive compounds, including antioxidants. However, to effectively recover these intracellular compounds, it is necessary to reduce the mass transfer resistances represented by the cellular envelope, within which they are localized, to enhance their extractability. To this purpose, emerging extraction technologies, have been proposed, including Supercritical Fluid Extraction, Microwave-Assisted Extraction, Ultrasound-Assisted Extraction, High-Pressure Homogenization, Pulsed Electric Fields, High Voltage Electrical Discharges. These technologies demonstrated to be a sustainable alternative to conventional extraction, showing the potential to increase the extraction yield, decrease the extraction time and solvent consumption. Additionally, in green extraction processes, also the contribution of solvent selection, as well as environmental and economic aspects, represent a key factor. Therefore, this review focused on critically analyzing the main findings on the synergistic effect of low environmental impact technologies and green solvents towards the green extraction of antioxidants from food by-products, by discussing the main associated advantages and drawbacks, and the criteria of selection for process sustainability.

Effect of nonthermal treatments on selected natural food pigments and color changes in plant material

In recent years, traditional high-temperature food processing is continuously being replaced by nonthermal processes. Nonthermal processes have a positive effect on food quality, including color and maintaining natural food pigments. Thus, this article describes the influence of nonthermal, new, and traditional treatments on natural food pigments and color changes in plant materials. Characteristics of natural pigments, such as anthocyanins, betalains, carotenoids, chlorophylls, and so forth available in the plant tissue, are shortly presented. Also, the characteristics and mechanism of nonthermal processes such as pulsed electric field, ultrasound, high hydrostatic pressure, pulsed light, cold plasma, supercritical fluid extraction, and lactic acid fermentation are described. Furthermore, the disadvantages of these processes are mentioned. Each treatment is evaluated in terms of its effects on all types of natural food pigments, and the possible applications are discussed. Analysis of the latest literature showed that the use of nonthermal technologies resulted in better preservation of pigments contained in the plant tissue and improved yield of extraction. However, it is important to select the appropriate processing parameters and to optimize this process in relation to a specific type of raw material.

Heat and Mass Transfer Modeling to Predict Temperature Distribution during Potato Frying after Pre-Treatment with Pulsed Electric Field

Based on unsteady state heat conduction, a mathematical model has been developed to describe the simultaneous heat and moisture transfer during potato frying. For the first time, the equation was solved using both enthalpy and Variable Space Network (VSN) methods, based on a moving interface defined by the boiling temperature of water in a potato disc during frying. Two separate regions of the potato disc namely fried (crust) and unfried (core), were considered as heat transfer domains. A variable boiling temperature of the water in potato discs was required as an input parameter for the model as the water is evaporated during frying, resulting in an increase in the soluble solid concentration of the potato sample. Pulsed electric field (PEF) pretreatment prior to frying had no significant effect on the measured moisture content, thermal conductivity or frying time compared to potatoes that did not receive a PEF pretreatment. However, a PEF pretreatment at 1.1 kV/cm and 56 kJ/kg reduced the temperature variation in the experimentally measured potato center by up to 30%. The proposed heat and moisture transfer model based on unsteady state heat conduction successfully predicted the experimental measurements, especially when the equation was solved using the enthalpy method.

Pulsed Electric Field (PEF) Enhances Iron Uptake by the Yeast Saccharomyces cerevisiae

The aim of the study was to investigate the influence of a pulsed electric field (PEF) on the level of iron ion accumulation in Saccharomyces cerevisiae cells and to select PEF conditions optimal for the highest uptake of this element. Iron ions were accumulated most efficiently when their source was iron (III) nitrate. When the following conditions of PEF treatment were used: voltage 1500 V, pulse width 10 μs, treatment time 20 min, and a number of pulses 1200, accumulation of iron ions in the cells from a 20 h-culture reached a maximum value of 48.01 mg/g dry mass. Application of the optimal PEF conditions thus increased iron accumulation in cells by 157% as compared to the sample enriched with iron without PEF. The second derivative of the FTIR spectra of iron-loaded and -unloaded yeast cells allowed us to determine the functional groups which may be involved in metal ion binding. The exposure of cells to PEF treatment only slightly influenced the biomass and cell viability. However, iron-enriched yeast (both with or without PEF) showed lower fermentative activity than a control sample. Thus obtained yeast biomass containing a high amount of incorporated iron may serve as an alternative to pharmacological supplementation in the state of iron deficiency.

Enhancing single-cell bioconversion efficiency by harnessing nanosecond pulsed electric field processing

Nanosecond pulsed electric field (nsPEF) processing is gaining momentum as a physical means for single-cell bioconversion efficiency enhancement. The technology allows biomass yields per substrate (Y_X/S) to be leveraged and poses a viable option for stimulating intracellular compound production. NsPEF processing thus resonates with myriad domains spanning the pharmaceutical and medical sectors, as well as food and feed production. The exact working mechanisms underlying nsPEF-based enhancement of bioconversion efficiency, however, remain elusive, and a better understanding would be pivotal for leveraging process control to broaden the application of nsPEF and scale-up industrial implementation. To bridge this gap, the study provides the electrotechnological and metabolic fundamentals of nsPEF processing in the bio-based domain to enable a critical evaluation of pathways underlying the enhancement of single-cell bioconversion efficiency. Evidence suggests that treating cells during the rapid proliferating and thus the early to mid-exponential state of cellular growth is critical to promoting bioconversion efficiency. A combined effect of transient intracellular and sublethal stress induction and effects caused on the plasma membrane level result in an enhancement of cellular bioconversion efficiency. Congruency exists regarding the involvement of transient cytosolic Ca²⁺ hubs in nsPEF treatment responses, as well as that of reactive oxygen species formation culminating in the onset of cellular response pathways. A distinct assignment of single effects and their contributions to enhancing bioconversion efficiency, however, remains challenging. Current applications of nsPEF processing comprise microalgae, bacteria, and yeast biorefineries, but these endeavors are in their infancies with limitations associated with a lack of understanding of the underlying treatment mechanisms, an incomplete reporting, insufficient characterization, and control of processing parameters. The study aids in fostering the upsurge of nsPEF applications in the bio-based domain by providing a basis to gain a better understanding of cellular mechanisms underlying an nsPEF-based enhancement of cellular bioconversion efficiency and suggests best practice guidelines for nsPEF documentation for improved knowledge transfer. Better understanding and reporting of processes parameters and consequently improved process control could foster industrial-scale nsPEF realization and ultimately aid in perpetuating nsPEF applicability within the bio-based domain.

Guidelines on reporting treatment conditions for emerging technologies in food processing

In the last decades, different non-thermal and thermal technologies have been developed for food processing. However, in many cases, it is not clear which experimental parameters must be reported to guarantee the experiments' reproducibility and provide the food industry a straightforward way to scale-up these technologies. Since reproducibility is one of the most important science features, the current work aims to improve the reproducibility of studies on emerging technologies for food processing by providing guidelines on reporting treatment conditions of thermal and non-thermal technologies. Infrared heating, microwave heating, ohmic heating and radiofrequency heating are addressed as advanced thermal technologies and isostatic high pressure, ultra-high-pressure homogenization sterilization, high-pressure homogenization, microfluidization, irradiation, plasma technologies, power ultrasound, pressure change technology, pulsed electric fields, pulsed light and supercritical CO₂ are approached as non-thermal technologies. Finally, growing points and perspectives are highlighted.

Resuscitation of Pulsed Electric Field-Treated Staphylococcus aureus and Pseudomonas putida in a Rich Nutrient Medium

Pulsed electric fields (PEFs) technology was reported to be useful as a disinfection method in the liquid food industry. This technology may lead to membrane permeabilization and bacterial death. However, resuscitation of viable but non-culturable cells and sublethally injured microorganisms in food was reported to be associated with foodborne outbreaks. The main aim of this study was to investigate the possible recovery of injured PEF-treated bacteria. The PEF treatment of Staphylococcus aureus and Pseudomonas putida led to a reduction of 3.2 log₁₀ and 4.8 log₁₀, respectively. After 5 h, no colony forming units (CFUs) were observed when the bacteria were suspended in phosphate buffer saline (PBS); and for 24 h, no recovery was observed. The PEF-treated S. aureus in brain-heart infusion (BHI) medium were maintained at 1.84 × 10⁴ CFU mL⁻¹ for about 1.5 h. While P. putida decreased to zero CFU mL⁻¹ by the 4th hour. However, after that, both bacteria recovered and began to multiply. Flow cytometry analysis showed that PEF treatment led to significant membrane permeabilization. Mass spectrometry analysis of PEF-treated P. putida which were suspended in BHI revealed over-expression of 22 proteins, where 55% were related to stress conditions. Understanding the recovery conditions of PEF-treated bacteria is particularly important in food industry pasteurization. To our knowledge, this is the first comprehensive study describing the recovery of injured PEF-treated S. aureus and P. putida bacteria.

Goals in Nutrition Science 2020-2025

Five years ago, with the editorial board of Frontiers in Nutrition, we took a leap of faith to outline the Goals for Nutrition Science - the way we see it (1). Now, in 2020, we can put ourselves to the test and take a look back. Without a doubt we got it right with several of the key directions. To name a few, Sustainable Development Goals (SDGs) for Food and Nutrition are part of the global public agenda, and the SDGs contribute to the structuring of international science and research. Nutritional Science has become a critical element in strengthening work on the SDGs, and the development of appropriate methodologies is built on the groundwork of acquiring and analyzing big datasets. Investigation of the Human Microbiome is providing novel insight on the interrelationship between nutrition, the immune system and disease. Finally, with an advanced definition of the gut-brain-axis we are getting a glimpse into the potential for Nutrition and Brain Health. Various milestones have been achieved, and any look into the future will have to consider the lessons learned from Covid-19 and the sobering awareness about the frailty of our food systems in ensuring global food security. With a view into the coming 5 years from 2020 to 2025, the editorial board has taken a slightly different approach as compared to the previous Goals article. A mind map has been created to outline the key topics in nutrition science. Not surprisingly, when looking ahead, the majority of scientific investigation required will be in the areas of health and sustainability. Johannes le Coutre, Field Chief Editor, Frontiers in Nutrition.

Pulsed electric field: An emerging pretreatment technology in a biogas production

This review focuses on current status of pulsed electric field (PEF) technology and its implementation in biogas production. First, basic principles of PEF and a schematic overview of typical PEF processing system were provided. Thereafter, lab- and pilot-scale PEF pretreatments of sludge with subsequent anaerobic digestion (AD) were provided. Furthermore, PEF technology, as an emerging technology for the lignocellulose (LC) pretreatment in biogas production which is still predominantly used at lab-scale, was outlined. Eventually, conclusion together with future perspectives and challenges were outlined.

Exploring the Effect of Pulsed Electric Fields on the Technological Properties of Chicken Meat

Pulsed electric field (PEF) is a non-thermal technology which is increasingly drawing the interest of the meat industry. This study aimed at evaluating the effect of PEF on the main technological properties of chicken meat, by investigating the role of the most relevant process parameters such as the number of pulses (150 vs. 300 and 450 vs. 600) and the electric field strength (0.60 vs. 1.20 kV/cm). Results indicated that PEF does not exert any effect on meat pH and just slightly affects lightness and yellowness. Low-intensity PEF treatments improved the water holding capacity of chicken meat by significantly (p < 0.001) reducing drip loss up to 28.5% during 4 days of refrigerated storage, without damaging proteins' integrity and functionality. Moreover, from the analysis of the process parameters, it has been possible to highlight that increasing the number of pulses is more effective in reducing meat drip loss rather than doubling the electric field strengths. From an industrial point of view, the results of this explorative study suggested the potential of PEF to reduce the undesired liquid inside the package, thus improving consumer acceptance.

Use of a Pulsed Electric Field to Improve the Biogas Potential of Maize Silage

Some types of biomass require great inputs to guarantee high conversion rates to methane. The complex structure of lignocellulose impedes its penetration by cellulolytic enzymes, as a result of which a longer retention time is necessary to increase the availability of nutrients. To use the full biogas potential of lignocellulosic substrates, a substrate pretreatment is necessary before the proper methane fermentation. This article discusses the impact of the pretreatment of maize silage with a pulsed electric field on biogas productivity. The experiment showed a slight decrease in cellulose, hemicellulose and lignin content in the substrate following pretreatment with a pulsed electric field, which resulted in a higher carbohydrate content in the liquid substrate fraction. The highest biogas production output was obtained for the pretreated sample at the retention time of 180 s for 751.97 mL/g volatile solids (VS), which was approximately 14% higher than for the control sample. The methane production rate for the control sample was 401.83 mL CH4/g VS, and for the sample following disintegration it was 465.62 mL CH4/g VS. The study found that pretreatment of maize silage with a pulsed electric field increased the biogas potential.

Eradication of Saccharomyces cerevisiae by Pulsed Electric Field Treatments

One of the promising technologies that can inactivate microorganisms without heat is pulsed electric field (PEF) treatment. The aim of this study was to examine the influence of PEF treatment (2.9 kV cm⁻¹, 100 Hz, 5000 pulses in trains mode of 500 pulses with a pulse duration of 10 µs) on Saccharomyces cerevisiae eradication and resealing in different conditions, such as current density (which is influenced by the medium conductivity), the sort of medium (phosphate buffered saline (PBS) vs. yeast malt broth (YMB) and a combined treatment of PEF with the addition of preservatives. When the S. cerevisiae were suspended in PBS, increasing the current density from 0.02 to 3.3 A cm⁻² (corresponding to a total specific energy of 22.04 to 614.59 kJ kg⁻¹) led to an increase of S. cerevisiae eradication. At 3.3 A cm⁻², a total S. cerevisiae eradication was observed. However, when the S. cerevisiae in PBS was treated with the highest current density of 3.3 A cm⁻², followed by dilution in a rich YMB medium, a phenomenon of cell membrane resealing was observed by flow cytometry (FCM) and CFU analysis. The viability of S. cerevisiae was also examined when the culture was exposed to repeating PEF treatments (up to four cycles) with and without the addition of preservatives. This experiment was performed when the S. cerevisiae were suspended in YMB containing tartaric acid (pH 3.4) and ethanol to a final concentration of 10% (v/v), which mimics wine. It was shown that one PEF treatment cycle led to a reduction of 1.35 log10, compared to 2.24 log10 when four cycles were applied. However, no synergic effect was observed when the preservatives, free SO₂, and sorbic acid were added. This study shows the important and necessary knowledge about yeast eradication and membrane recovery processes after PEF treatment, in particular for application in the liquid food industry.

Pulsed Electric Field Treatment Promotes Lipid Extraction on Fresh Oleaginous Yeast Saitozyma podzolica DSM 27192

This study reports on the use of pulsed electric field (PEF) as a pre-treatment step to enhance lipid extraction yield using extraction with ethanol-hexane blend on fresh oleaginous yeast Saitozyma podzolica. The yeasts were cultivated on nitrogen-depleted condition and had a lipid content of 26.4 ± 4.6% of dry weight. PEF-treatment was applied on the yeast suspension either directly after harvesting (unwashed route) or after a washing step (washed route) which induced a reduction of conductivity by a factor eight. In both cases, cell concentration was 20 g of biomass per liter of suspension. In the unwashed route, the lipid extraction efficiency increased from 7% (untreated) to 54% thanks to PEF-treatment. In case an additional washing step was added after PEF-treatment, up to 81% of the lipid content could be recovered. The washed route was even more efficient since lipid extraction yields increased from 26% (untreated) to 99% of total lipid. The energy input for the PEF-treatment never exceeded 150 kJ per liter of initial suspension. The best lipid recovery scenario was obtained using pulses of 1 μs, an electric field of 40 kV/cm and it required slightly less than 11 MJ/kg_LIPID. This amount of energy can be further reduced by at least a factor five by optimizing the treatment and especially by increasing the concentration of the treated biomass. The process can be easily up-scaled and does not require any expensive handling of the biomass such as freezing or freeze-drying. These findings demonstrate the potential benefit of PEF-treatment in the downstream processing of oleaginous yeast. From a basic research point of view, the influence of conductivity on PEF energy requirements and extraction yields was examined, and results suggest a higher efficiency of PEF-treatment in terms of energy when treatment is performed at lower conductivity.

Non-thermal pasteurization of lipid emulsions by combined supercritical carbon dioxide and high-power ultrasound treatment

Supercritical carbon dioxide (SC-CO₂) is a novel method for food pasteurization, but there is still room for improvement in terms of the process shortening and its use in products with high oil content. This study addressed the effect of high power ultrasound (HPU) on the intensification of the SC-CO₂ inactivation of E. coli and B. diminuta in soybean oil-in-water emulsions. Inactivation kinetics were obtained at different pressures (100 and 350 bar), temperatures (35 and 50 °C) and oil contents (0, 10, 20 and 30%) and were satisfactorily described using the Weibull model. The experimental results showed that for SC-CO₂ treatments, the higher the pressure or the temperature, the higher the level of inactivation. Ultrasound greatly intensified the inactivation capacity of SC-CO₂, shortening the process time by approximately 1 order of magnitude (from 50 to 90 min to 5-10 min depending on the microorganism and process conditions). Pressure and temperature also had a significant (p < 0.05) effect on SC-CO₂ + HPU inactivation for both bacteria, although the effect was less intense than in the SC-CO₂ treatments. E. coli was found to be more resistant than B. diminuta in SC-CO₂ treatments, while no differences were found when HPU was applied. HPU decreased the protective effect of oil in the inactivation and similar microbial reductions were obtained regardless of the oil content in the emulsion. Therefore, HPU intensification of SC-CO₂ treatments is a promising alternative to the thermal pasteurization of lipid emulsions with heat sensitive compounds.

Temperature and presence of ethanol affect accumulation of intracellular trehalose in Lactobacillus plantarum WCFS1 upon pulsed electric field treatment

Pulsed electric field (PEF) treatment can be used to increase intracellular small molecule concentrations in bacteria, which can lead to enhanced robustness of these cells during further processing. In this study we investigated the effects of the PEF treatment temperature and the presence of 8% (v/v) ethanol in the PEF medium on cell survival, membrane fluidity and intracellular trehalose concentrations of Lactobacillus plantarum WCFS1. A moderate PEF treatment temperature of 21 °C resulted in a high cell survival combined with higher intracellular trehalose concentrations compared to a treatment at 10 and 35 °C. Interestingly, highest intracellular trehalose concentrations were observed upon supplementing the PEF medium with 8% ethanol, which resulted in more than a doubling in intracellular trehalose concentrations, while culture survival was retained. Overall, this study shows that treatment temperature and PEF medium optimization are important directions for improving molecule uptake upon PEF processing.

Understanding the occurrence of tailing in survival curves of Salmonella Typhimurium treated by pulsed electric fields

This study aimed to gain more in-depth knowledge of the mechanisms involved in microbial inactivation by pulsed electric fields (PEF) to understand the tailing observed in survival curves of Salmonella Typhimurium (STCC 878). The comparison of the inactivation achieved by the application of one train of pulses with those obtained with pulses applied in two trains shows that the tail of the survival curves was a consequence of a transient increment of the microbial resistance to the effect of the electric field in a proportion of the cells. After some time following the application of the first pulse train, cells became again sensitive to the second train, and tailing tended to disappear. The required time was highly dependent on the characteristics of the incubation medium. Similar effects were observed when the treatments were validated on whole milk and orange juice. This study has demonstrated by the first time on microbial cells the benefits of splitting the delivered PEF treatment in two trains with a period of delay between them. Therefore, this insight opens up the possibility of developing new strategies to achieve the required inactivation levels to guarantee food safety by moderate PEF treatments.

Evaluation of pulsed electric fields technology for the improvement of subsequent carotenoid extraction from dried Rhodotorula glutinis yeast

This research aims to evaluate whether the electroporation of Rhodotorula glutinis fresh biomass improved the subsequent extraction of carotenoids from dry biomass using supercritical CO2 and traditional solvent extraction. Supercritical CO2 extraction yields were low after all treatments assayed. Similarly, solvent extraction of carotenoids from untreated or PEF treated cells that were immediately freeze-dried after the pre-treatment was neither effective (extraction yield < 20% total content). Conversely, PEF-treatment and subsequent intermediate incubation in aqueous buffer for 24 h, followed by freeze-drying and extraction, led to a large improvement with the three solvents assayed (acetone, hexane, ethanol). Ethanol was the most efficient, reaching an extraction yield of 80% of total carotenoid, which represents a recovery of 267 µg/gdw. Torularhodin esters constituted the main carotenoid found in the extracts. This is of great interest, as ethanol is eco-friendly solvent and potential applications of torularhodin range from food to medical purposes.

Kinetic Modeling and Numerical Simulation as Tools to Scale Microalgae Cell Membrane Permeabilization by Means of Pulsed Electric Fields (PEF) From Lab to Pilot Plants

Pulsed Electric Fields (PEF) is a promising technology for the gentle and energy efficient disruption of microalgae cells such as Chlorella vulgaris. The technology is based on the exposure of cells to a high voltage electric field, which causes the permeabilization of the cell membrane. Due to the dependency of the effective treatment conditions on the specific design of the treatment chamber, it is difficult to compare data obtained in different chambers or at different scales, e.g., lab or pilot scale. This problem can be overcome by the help of numerical simulation since it enables the accessibility to the local treatment conditions (electric field strength, temperature, flow field) inside a treatment chamber. To date, no kinetic models for the cell membrane permeabilization of microalgae are available what makes it difficult to decide if and in what extent local treatment conditions have an impact on the permeabilization. Therefore, a kinetic model for the perforation of microalgae cells of the species Chlorella vulgaris was developed in the present work. The model describes the fraction of perforated cells as a function of the electric field strength, the temperature and the treatment time by using data which were obtained in a milliliter scale batchwise treatment chamber. Thereafter, the model was implemented in a CFD simulation of a pilot-scale continuous treatment chamber with colinear electrode arrangement. The numerical results were compared to experimental measurements of cell permeabilization in a similar continuous treatment chamber. The predicted values and the experimental data agree reasonably well what demonstrates the validity of the proposed model. Therefore, it can be applied to any possible treatment chamber geometry and can be used as a tool for scaling cell permeabilization of microalgae by means of PEF from lab to pilot scale. The present work provides the first contribution showing the applicability of kinetic modeling and numerical simulation for designing PEF processes for the purpose of biorefining microalgae biomass. This can help to develop new processes and to reduce the costs for the development of new treatment chamber designs.

Mechanistic view of skin electroporation - models and dosimetry for successful applications: an expert review

Introduction: Skin electroporation is a promising treatment for transdermal drug delivery, gene electrotransfer, skin rejuvenation, electrochemotherapy, and wound disinfection. Although a considerable amount of in vitro and in vivo studies exists, the translation to clinics is not as fast as one would hope. We hypothesize the reason lies in the inadequate dosimetry, i.e. electrode configurations, pulse parameters, and pulse generators used. We suggest adequate dosimetry can be determined by mathematical modeling which would allow comparison of protocols and facilitate translation into clinics.Areas covered: We introduce the mechanisms and applications of skin electroporation, present existing mathematical models and compare the influence of different model parameters. We review electrodes and pulse generators, prototypes, as well as commercially available models.Expert opinion: The reasons for slow translation of skin electroporation treatments into clinics lie in uncontrolled and inadequate dosimetry, poor reporting rendering comparisons between studies difficult, and significant differences in animal and human skin morphology often dismissed in reports. Mathematical models enable comparison of studies, however, when the parameters of the pulses and electrode configuration are not adequately reported, as is often the case, comparisons are difficult, if not impossible. For each skin electroporation treatment, systematic studies determining optimal parameters should be performed and treatment parameters standardized.

Effect of pulsed electric fields and high pressure on improved recovery of high-added-value compounds from olive pomace

Olive pomace is considered a solid by-product and a rich source of valuable compounds such as polyphenols, flavonoids with antioxidant properties, and proteins. Nonthermal technologies, which cause alterations to cell permeability, are being explored to assist conventional recovery techniques. The aim of this study was to assess the effect of pulsed electric fields (PEF) and high pressure (HP) on improved recovery yield of the high-added-value compounds or to shorten the extraction time of these compounds. Olive pomace (Tsounati cv) was pretreated with PEF (1.0 to 6.5 kV/cm, 0.9 to 51.1 kJ/kg, and 15 µs pulse width) or HP (200 to 600 MPa and 0 to 40 min). Evaluation of the intracellular compounds extracted via solid-liquid extraction (50% ethanol-water solution) was performed. More intense PEF and HP conditions resulted in a significant increase of the phenolic concentration up to 91.6% and 71.8%, respectively. The increased antioxidant capacity of each extract was correlated to phenolic compound concentration. The protein concentration that was achieved with PEF pretreatment was doubled; however, HP-pretreated extracts reached 88.1% higher yield than untreated for pressures up to 200 MPa. HP and PEF pretreatment decreased extraction completion time t₉₈ (needed time to recover the equal amount of phenolics and proteins of untreated after 60 min of conventional extraction) to 12 min and lower than 1 min, respectively. To conclude, both pretreatments are effective in improving the conventional extraction process for increased yield recovery of high-added-value compounds from olive pomace.

Pretreatment of microalgal biomass for efficient biohydrogen production - Recent insights and future perspectives

Biohydrogen is a plausible alternative fuel solution for the contemporary issues regarding global warming and the steadily increasing greenhouse gas emissions, because of its high energy content and carbon-free combustion properties. Hydrogen does not exist in its natural state and the current hydrogen production technologies (steam methane reforming, water splitting) are energy-intensive, accompanied by a huge carbon footprint. Dark fermentative hydrogen production by anaerobic hydrogen-producing bacteria is a green, sustainable and emission-free pathway for hydrogen production. Microalgal biomass is considered as the third generation biofuel feedstock and is receiving academic and industrial research attention for its carbon sequestration abilities. This review discusses in detail about the pretreatment methods that could be adapted for microalgal biomass for effective biohydrogen production. Microalgal cell wall structure and the associated polymeric carbohydrates that offer certain recalcitrance are critically analyzed and future research perspectives are presented.

Influence of Pulsed Electric Field on Accumulation of Calcium in Lactobacillus rhamnosus B 442

Calcium is an element that performs many important functions in the human body. A study was conducted on the use of a pulsed electric field (PEF) to enrich cells of Lactobacillus rhamnosus B 442 in calcium ions. The highest concentration of calcium ions in bacterial cells (7.30 mg/g d.m.) was obtained at ion concentration of 200 µg/ml of medium and with the use of the following PEF parameters: field strength 3.0 kV/cm, exposure time 10 min, pulse width 75 ms and 20 h of culturing after which bacteria were treated with the field. Cell biomass varied in the range from 0.09 g/g d.m. to 0.252 g/g d.m., and the total number of bacteria ranged from 10¹⁰ CFU/ml to 10¹² CFU/ml. Microscope photographs prove that calcium ions were situated within the cells of the bacteria, and electroporation contributed to an increase in the effectiveness of the ion bioaccumulation process. Samples containing calcium and subjected to electroporation displayed intensive fluorescence. The significance of this research was the possibility of using probiotic bacteria enriched with calcium ions for the production of functional food in subsequent studies.