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

The application of pulsed electric field (PEF) technology as a non-thermal cell membrane permeabilization treatment, was widely demonstrated widely to be effective in microbial inactivation studies, as well as to increase the rates of heat and mass transfer phenomena in food and biotechnological processes (drying, osmotic treatment, freezing, extraction, and diffusion). Nevertheless, most published papers on the topic do not provide enough information for other researchers to assess results properly. A general rule/guidance in reporting experimental data and most of all exposure conditions, would be to report details to the extent that other researchers will be able to repeat, judge and evaluate experiments and data obtained. This is what is described in the present recommendation paper. Industrial relevance: Pulsed electric field (PEF) treatment is a promising technology that has received considerable attention in food and biotechnology related applications food and biotechnology related applications of PEF include: i) “cold” pasteurization of liquid foods and disinfection of wastewater by microbial inactivation ii) PEF-assisted processing (drying, extraction or expression

Quantification of metal release from stainless steel electrodes during conventional and pulsed ohmic heating

Electrochemical reactions at the electrode-solution interface of an ohmic heater can be avoided or significantly limited by choosing appropriate processing conditions in relation to the food properties. In the present work the effect of the electrical parameters (electric field strength and frequency of the applied current signal) and product factors (halides concentration, electrical conductivity and pH) on metal release from stainless steel (type AISI 316 L) electrodes of a batch ohmic heater was investigated. In each experiment, the concentrations of the main constituents of stainless steel (iron, chromium and nickel) released in the heating medium were detected by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Atomic Absorption Spectrophotometry (AAS). Results showed that the rate of metal release from the electrodes to the heating medium depends on frequency and applied field strength. However, the use of ohmic heating at a higher frequency than conventional (50 Hz) can significantly (p ≤ 0.05) reduce the flux of metal ions from stainless steel electrodes. Moreover, it was also demonstrated that electrochemical phenomena occurring at the electrode-solution interface strongly depend on the composition, pH and electrical conductivity of the heating medium. Industrial relevance: The magnitude of electrode material released into the heating medium during ohmic processing depends on many factors, whose effects should be known in order to define optimal treatment conditions, electrode material and food properties able to avoid or minimize the undesired phenomenon of contamination of the food product, electrode-fouling and electrode corrosion. This paper contributes to clarifying the effects of electric field strength applied as well as electrical conductivity, pH, and presence of halides in the heating medium on electrode corrosion or release of electrode materials during high frequency (25 kHz, bipolar square wave) pulsed power OH in comparison with conventional (50 Hz sine wave) OH. Interestingly, the use of sufficiently large frequencies may avoid or reduce the extent of electrochemical reactions at the electrode interface, minimizing corrosion and leakage of metals to the heating medium, even when electrode material of low cost and electrochemically active like stainless steel is used

Ultrasound-assisted green solvent extraction of high-added value compounds from microalgae Nannochloropsis spp.

The aim of this work was to investigate ultrasound (US)-assisted green solvent extraction of valuable compounds from the microalgae Nannochloropsis spp. Individual green solvents (water, ethanol (EtOH), dimethyl sulfoxide (DMSO)) and binary mixture of solvents (water-DMSO and water-EtOH) were used for the extraction procedures. Maximum total phenolic compounds yield (Yp 0.33) was obtained after US pre-treatment (W = 400 W, 15 min), being almost 5-folds higher compared to that found for the untreated samples and aqueous extraction (Yp 0.06). The highest yield of total chlorophylls (Yc 0.043) was obtained after US (W = 400 W, 7.5 min), being more than 9-folds higher than those obtained for the untreated samples and aqueous extraction (Yc 0.004). The recovery efficiency decreased as DMSO > EtOH > H2O. The optimal conditions to recover phenolic compounds and chlorophylls from microalgae were obtained after US pre-treatment (400 W, 5 min), binary mixtures of solvents (water-DMSO and water-EtOH) at 25–30%, and microalgae concentration of 10%

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

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

Selective extraction of intracellular components from the microalga Chlorella vulgaris by combined pulsed electric field–temperature treatment

The synergistic effect of temperature (25–65 C) and total specific energy input (0.55–1.11 kWh kgDW 1 ) by pulsed electric field (PEF) on the release of intracellular components from the microalgae Chlorella vulgaris was studied. The combination of PEF with temperatures from 25 to 55 C resulted in a conductivity increase of 75% as a result of cell membrane permeabilization. In this range of temperatures, 25–39% carbohydrates and 3–5% proteins release occurred and only for carbohydrate release a synergistic effect was observed at 55 C. Above 55 C spontaneous cell lysis occurred without PEF. Combined PEF–temperature treatment does not sufficiently disintegrate the algal cells to release both carbohydrates and proteins at yields comparable to the benchmark bead milling (40–45% protein, 48–58% carbohydrates)

Innovative alternative technologies to extract carotenoids from microalgae and seaweeds

Marine microalgae and seaweeds (microalgae) represent a sustainable source of various bioactive natural carotenoids, including β-carotene, lutein, astaxanthin, zeaxanthin, violaxanthin and fucoxanthin. Recently, the large-scale production of carotenoids from algal sources has gained significant interest with respect to commercial and industrial applications for health, nutrition, and cosmetic applications. Although conventional processing technologies, based on solvent extraction, offer a simple approach to isolating carotenoids, they suffer several, inherent limitations, including low efficiency (extraction yield), selectivity (purity), high solvent consumption, and long treatment times, which have led to advancements in the search for innovative extraction technologies. This comprehensive review summarizes the recent trends in the extraction of carotenoids from microalgae and seaweeds through the assistance of different innovative techniques, such as pulsed electric fields, liquid pressurization, supercritical fluids, subcritical fluids, microwaves, ultrasounds, and high-pressure homogenization. In particular, the review critically analyzes technologies, characteristics, advantages, and shortcomings of the different innovative processes, highlighting the differences in terms of yield, selectivity, and economic and environmental sustainability

PEF treatment for the valorization of agri-food byproducts

Cell membrane acts as a physical barrier when removing the intracellular substances (water, juices and solutes) from food tissues in common unit operations of food industry such as drying and extraction. The permeabilization of the cell membrane by means of food tissue pre-treatments may positively affect the mass transport rates, and, thus, higher yield and shorter residence time in the processing plants can be obtained. However, the conventional pre-treatments of the raw material utilized to increase the extraction yield, namely grinding, heating, addition of chemicals/enzymes, have a negative impact on the quality of the solutions and extracts (e.g., purity, turbidity, color, flavor and nutrient content). Pulsed electric fields (PEF) treatments has been proved to bea promising mild and more efficient physical method alternative to conventional cell disintegration techniques. The exposure of food tissue to an electric field of moderate intensity (0.5-10 kV/cm) and relatively low energy (1-10 kJ/kg), applied in the form of repetitive very short voltage pulses, typically from few μs up to 1 ms, induces thepermeabilization of cell membranes by electroporation, facilitating the release of liquids and valuable compounds from the inner parts of the cells. PEF pretreatment may exert a selective permeabilization of the membranes (tonoplast and plasma membrane), while the cell wall remains intact. Consequently, the yield and the purity of the extractsare improved. Moreover, since PEF is a non-thermal technology, the reduction of the impact on the thermo-sensitive and thermo-labile compounds in the extracts is avoided. Interestingly, PEF treatment can be used to recover valuable compounds from food wastes and by-products,which have been matter of concern by the agri-food industry due to their environmental impact. The compounds that can be recovered show great potential industrial applications as natural colorants (anthocyainins, carotenoids, betanines, etc.) or nutraceuticals(polyphenols). In this paper a brief description of the basic mechanisms of electroporation of plant tissues is presented and the experimental results on the recovery of valuable compounds from fruit and vegetable by-products are presented. The influence of PEF processing parameters on extraction effectiveness is also discussed

Preface

Heat remains the dominant microbial/enzyme inactivation technique used in food preservation though its impact on food quality is often at odds with increased consumer demand for minimally processed (MP) products. Traditional heat processes are very successful for microbial and enzyme inactivation but can also cause undesirable protein denaturation, non-enzymatic browning and loss of vitamins/volatile flavour compounds in some food matrices. As a result, the use of traditional heat processes on MP products (which have characteristics such as higher quality and natural) cannot be reduced by compensating with other traditional chemical preservation strategies as these products are also preferred to be additive and preservative free. However, more recently, alternative preservation technologies have been developed (e.g. high hydrostatic pressure (HPP), high voltage pulsed electrical fields (PEF), ultrasound (US), ultraviolet light (UV) and high intensity light pulses (HILP)). These also have the capability to inactive microorganisms and enzymes, but do so by non-thermal means and therefore their use potentially aligns with the MP ethos. Of these technologies, there have been numerous volumes written on HPP, PEF, US and UV but this is the first book which focuses primarily on the use of high intensity light in food processing. It begins by describing UV light but then distinguishes UV from HILP (which is encompasses a much broader light spectrum). It subsequently gives the reader an insight into the generation of HILP, the application of HILP to foods with reference to its impact on microbial inactivation, quality and nutritional parameters. It also explores the efficacy of this technology for microbial inactivation in combination with other technologies in a hurdle approach while also considering the regulatory issues associated with the use of new preservation technologies. Other non-preservation applications are also considered including a comprehensive chapter on the use of this technology in medical environments. The book is targeted at professional food technologists working in the food industry, academic staff members responsible for the delivery of food preservation operations courses and upper-level undergraduates and masters-level students taking degrees in Food Technology or Food Science. The authors are all highly regarded in the field of HILP and have made a significant contribution to knowledge on this field with numerous publications in this technology