Pulsed electric field assisted sunflower oil pilot production: Impact on oil yield,extraction kinetics and chemical parameters

Sunflower oil pilot-production based on local raw materials assisted by pulsed electric field (PEF), which is produced in terms of oil yield, extraction kinetics and chemical parameters on pilot scale mill with continuous-flow material treatment developed in this work. PEF treatment with electric field strength 7 kV/cm and energy consumption of 6.1 kJ/kg on the sunflower seed increased the value of extraction yield by 2.3%, with respect to a control one. Extraction parameters obtained by pulsed electric field treatment showed that diffusion coefficient, micropore volume, and disintegration index were significantly higher than control ones (on 55.5%, 32.2% and 43% respectively). Furthermore, the use of PEF treatment had minor effects on the main chemical characteristics (acid and peroxide value etc.) and color parameters of the sunflower oil. On the basis of obtained results, it can be concluded that PEF could be a high potential industrial technology to improve enriched in human-health-related compounds of sunflower oil.Practical applicationsThe obtained results are relevant for specialists using PEF technologies and developing PEF equipment. The data will also be in demand when calculating the economic efficiency of PEF application on an industrial scale.     

Influence of Pulsed Electric Fields processing at high-intensity electric field strength on the relationship between anthocyanins composition and colour intensity of Merlot (Vitis vinifera L.) musts during cold maceration

Merlot grapes have high proportion of anthocyanins protected inside cell vacuoles but the thick skins limit their extractability. This study investigated the effect of a continuous Pulsed Electric Fields (PEF at 500 kg/h) system operated at high-intensity electric field strengths (>30 kV/cm) combined with energy inputs ranging from 4.7 to 49.4 kJ/L on anthocyanins extraction and colour intensity of Merlot musts during a 4-day cold maceration. Considerable amount of anthocyanins with different chemical features was extracted instantaneously due to PEF treatment at high-intensity electric field strength, in which the amount was higher than those extracted from non PEF-treated Merlot followed by 4 days maceration. During maceration, malvidin derivatives were the most significant anthocyanins contributing (r > 0.71, p < 0.05) to the changes in colour intensity of PEF-treated musts. This finding suggests that malvidin derivatives are good indicators to predict the efficiency of specific PEF process condition in reducing the length of cold maceration while achieving maximum colour intensity in the musts. This research is important either for the wine and beverage industries.Industrial relevance textPrevious PEF studies mainly investigated the effect of low-intensity electric field strength (<7 kV/cm) on various grapevine varieties, the current study investigated the effect of PEF on grapes at high-intensity electric field strength (>30 kV/cm) using Marx generator for the first time in the literature. Marx generator has a tendency to produce high-intensity electric field strength, up to 80 kV/cm, but the impact on plant materials intended for food application are not well studied. In this study, Merlot grapes were continuously treated with PEF at high-intensity electric field strength at a flow rate of 500 kg/h while many previous studies conducted trial at approximately 100–200 kg/h in conjunction with low-intensity electric field strength (<7 kV/cm). Therefore, it seems necessary to advance the current application of PEF for grape processing to high-intensity electric field strength in order to cope with or fit into the standard production rate (>200 kg/h) at the commercial scale. In this study, we have successfully showed that high-intensity electric field strengths (33.1 and 41.5 kV/cm) of PEF were efficient (i.e. instantaneous extraction) in extracting all types of anthocyanins with different chemical features from the thick-grape skins of Merlot. Therefore, grape juice with more elaborated anthocyanin composition and intense colour was produced at a large scale immediately after PEF. The extracted anthocyanins were found to be stable over time after PEF treatment in which the issues on anthocyanin stability and colour development have never been considered in many previous studies, but are important quality aspects that beverage industry desired.     

Evaluation of phenolic extraction during fermentation of red grapes treated by a continuous pulsed electric fields process at pilot-plant scale

The feasibility of processing red grapes by pulsed electric fields (PEF) at pilot-plant scale to improve the extraction of anthocyanins and phenols during the maceration-fermentation step of the winemaking process has been investigated. With this general purpose a colinear continuous treatment chamber was developed. The influence of field strength (2, 5 and 7 kV/cm) and grape variety (Cabernet Sauvignon, Syrah and Merlot) in the extraction kinetics was studied. Extraction curves were described by an exponential equation that permits to estimate the extraction rate (k) and the maximum extraction yield (Y_max). An increment of the electric field from 2 to 7 kV/cm increased the extraction rate of anthocyanins and total phenols for the three varieties investigated. The increment of Y_max due to the application of PEF was more remarkable in Cabernet Sauvignon than in Merlot and Syrah. The continuous PEF system presented in this work constitutes an important step for the application of PEF technology at commercial scale.     

Minimization of thermal impact by application of electrode cooling in a co-linear PEF treatment chamber

A co-linear pulsed electric field (PEF) treatment chamber was analyzed and optimized considering electrical process conditions, temperature, and retention of heat-sensitive compounds during a continuous PEF treatment of peach juice. The applicability of a jacket heat-exchanger device surrounding the ground electrode was studied in order to provide active cooling and to avoid temperature peaks within the treatment chamber thus reducing the total thermal load to which the product is exposed. Simulation of the PEF process was performed using a finite element method prior to experimental verification. Inactivation of polyphenoloxydase (PPO) and peroxidase (POD) as well as the degradation of ascorbic acid (AA) in peach juice was quantified and used as indirect indicators for the temperature distribution. Peaks of product temperature within the treatment chamber were reduced, that is, from 98 to 75 °C and retention of the indicators PPO, POD, and AA increased by more than 10% after application of the active electrode cooling device. Practical Application: The co-linear PEF treatment chamber is widely used for continuous PEF treatment of liquid products and also suitable for industrial scale application; however, Joule heating in combination with nonuniform electric field distribution may lead to unwanted thermal effects. The proposed design showed potential to reduce the thermal load, to which the food is exposed, allowing the retention of heat-sensitive components. The design is applicable at laboratory or industrial scale to perform PEF trials avoiding temperature peaks, which is also the basis for obtaining inactivation kinetic models with minimized thermal impact on the kinetic variables.     

Effect of dimensions and geometry of co-field and co-linear pulsed electric field treatment chambers on electric field strength and energy utilisation

Approximations of the electric field strength and specific energy input of continuous pulsed electric field (PEF) systems often assume parallel plate configurations. However, it is known that actual electric field strengths and specific energy inputs can be significantly different from this simplistic approach. A systematic study of more than 150 dimensions and various insulator geometries of pilot-scale PEF treatment chambers with co-linear electrode configuration was performed. A reduction of the inner diameter of the insulator and its shape changes the distribution and (average) intensity of the electric field. Both, the average electric field strength of the PEF treatment zone and the actual specific energy input, were significantly lower than the expected values derived from dividing the applied voltage by the electrode gap. The difference between theoretical and actual values generally increased with increasing electrode radius and decreasing electrode gap. The relative ratios of theoretical electric field strength or specific energy input to actual (average) electric field strength or specific energy input showed a linear dependency on the ratio of electrode radius and gap. The determined relationships of specific energy input and treatment chamber dimensions and geometry were experimentally validated in four different PEF treatment chambers.     

An investigation on pulsed electric fields technology using new treatment chamber design

A pulsed electric field (PEF) system was designed and constructed using modern IGBT technology. The main focus of this work was to design a new PEF treatment chamber that operate at high electric field intensities with limited increase in liquid temperature and limited fouling of electrodes. Four multi-pass treatment chambers were designed consisting of two stainless steel mesh electrodes in each chamber, with the treated fluid flowing through the openings of the mesh electrodes. The two electrodes are electrically isolated from each other by an insulator element designed to form a small orifice where most of the electric field is concentrated. Dielectric breakdown inside the chambers was prevented by removing the electrodes far from the narrow gap. The effect of PEF treatment on the inactivation of gram-negative Escherichia coli ATCC 25922 suspended in simulated milk ultra-filtrate (SMUF) of 100%, 66.67% and 50% w/w was investigated. Treatments with the same electrical input power but with higher electric field strengths provided larger degree of killing. The effect of PEF treatment using suspensions at different flow rates and different pulse frequencies was also investigated. In general, the inactivation rate of E. coli increased with increasing electric field strength, treatment time and processing temperature. More than 6 log reductions in E. coli suspended in SMUF was achieved using electric field intensity in the range of (37.2–49.6 kV/cm) with a treatment temperature not exceeding 38 °C.Industrial relevanceThis paper presents an innovative pulsed electric field system for non-thermal pasteurisation of liquid food. The system design provides uniform distribution of electric field and minimum fouling of electrodes. This PEF system can be scaled up to any industrial size, making it attractive for industrial applications.     

Coupled electrical-fluid model of pulsed electric field treatment in a model food system

A coupled electrical-fluid model of a pulsed electric field (PEF) treatment is presented. The modeling of PEF food treatment to date has been limited to a separate study of the electric field distribution and the product flow. A model was developed that couples the electric field and fluid dynamics analysis. The main feature of the model is that parameters vital for the process control, i.e. the product flow and heating and the electric field distribution in a PEF chamber, can be determined self-consistently. Comparison between model predictions and experimental measurements were made for a laboratory scale, co-field treatment chamber configuration of a continuous flow-through PEF unit. The predicted product temperatures downstream of the treatment chamber were in good agreement with the observed temperature for a range of conditions considered. This work is a first step towards developing a reliable tool for the optimization of the PEF treatment chamber geometry.     

Impact of Electric Pulse Treatment on Selective Extraction of Intracellular Compounds from Saccharomyces cerevisiae Yeasts

Treatments by high-voltage electrical discharges (HVED, needle-plate electrode geometry, U?=?40 kV, t _p?≈?0.5 μs) and pulsed electric field (PEF, plate–plate electrode geometry, E?=?5–40 kV/cm, t _p?≈?8.3 μs) were evaluated as tools for selective extraction of different intracellular components from the wine Saccharomyces cerevisiae (bayanus) yeasts in a 0.5% (w/w) aqueous suspension. The pulses in the form of damped oscillations and exponential decay were applied in HVED and PEF modes of treatment, respectively. The extraction efficiency results obtained using HVED and PEF techniques were compared with those for high-pressure homogenization technique. The HVED and PEF treatments always resulted in incomplete damage of yeast cells, though efficiency of HVED was higher than that of PEF. The high selectivity of extraction of ionic substances, proteins, and nucleic acids was demonstrated; e.g., electric pulse treatments at E?=?40 kV/cm and N?=?500 allowed extraction of ≈80% and ≈70% of ionic substances, ≈4% and ≈1% of proteins and ≈30% and ≈16% of nucleic acids in cases of HVED and PEF modes, respectively.     

Pulsed electric field‐assisted extraction of valuable compounds from microorganisms

Microorganisms (bacteria, yeast, and microalgae) are a promising resource for products of high value such as nutrients, pigments, and enzymes. The majority of these compounds of interest remain inside the cell, thus making it necessary to extract and purify them before use. This review presents the challenges and opportunities in the production of these compounds, the microbial structure and the location of target compounds in the cells, the different procedures proposed for improving extraction of these compounds, and pulsed electric field (PEF)‐assisted extraction as alternative to these procedures. PEF is a nonthermal technology that produces a precise action on the cytoplasmic membrane improving the selective release of intracellular compounds while avoiding undesirable consequences of heating on the characteristics and purity of the extracts. PEF pretreatment with low energetic requirements allows for high extraction yields. However, PEF parameters should be tailored to each microbial cell, according to their structure, size, and other factors affecting efficiency. Furthermore, the recent discovery of the triggering effect of enzymatic activity during cell incubation after electroporation opens up the possibility of new implementations of PEF for the recovery of compounds that are bounded or assembled in structures. Similarly, PEF parameters and suspension storage conditions need to be optimized to reach the desired effect. PEF can be applied in continuous flow and is adaptable to industrial equipment, making it feasible for scale‐up to large processing capacities.     

高压脉冲电场同轴处理室的仿真优化

高压脉冲电场杀菌技术是一种新型非热杀菌技术,处理室用来装载待处理物料并在处理室内直接施加脉冲电场。针对自主设计的一种电极间距可调、处理室内腔体可更换的新型中试规模的同轴处理室,使用COMSOL软件建立脉冲电场杀菌系统三场耦合的数学模型模拟处理室内的电场强度、流料特性及温度分布,为同轴处理室的结构优化提供依据。仿真结果表明正电极内圆边缘处的电场强度不均匀,对正电极倒圆角后的处理室更为适用。     

Inactivation of L. plantarum in a PEF microreactor: The effect of pulse width and temperature on the inactivation

This article describes the inactivation of Lactobacillus plantarum by pulsed electric fields (PEF) in a microfluidic reactor. The microreactor has the specific advantage that the field intensity can be extremely high with accurate control and measurement of the pulse shape, combined with good temperature controllability. It is demonstrated that the temperature increase due to the ohmic heating of the fluid during treatment is marginal, thereby making this an excellent device for decoupling the temperature and electric field effects of PEF. Flow cytometry measurements showed that the electroporation of cells by PEF is a gradual effect. Reducing the pulsewidth at equal energy inputs did not show a change in inactivation. Higher temperatures showed higher inactivation rates. The effect of the temperature and the electric field strength could be described by a model that combines an Arrhenius equation for temperature dependency with either a Huelsheger or an activation energy based model for electric field dependency.Industrial relevanceThe product temperature is increasing during pulsed electric field treatment due to ohmic heating. Up to now, it was not possible to distinguish between the electric and heat effects that take place in the reactor. With the presented PEF microreactor, it was possible to make this distinction, which can help in the development of new, optimized PEF reactors.     

High-voltage pulsed electric field laboratory device with asymmetric voltage multiplier for marine macroalgae electroporation

Optimization of protocols is required for each specific type of biomass processed by electroporation of the cell membrane with high voltage pulsed electric fields (PEF). Such optimization requires convenient and adaptable laboratory systems, which will enable determination of both electrical and mechanical parameters for successful electroporation and fractionation. In this work, we report on a laboratory PEF system consisting of a high voltage generator with a novel asymmetric voltage multiplying architecture and a treatment chamber with sliding electrodes. The system allows applying pulses of up to 4 kV and 1 kA with a pulse duration between 1 μs and 100 μs. The allowable energy dissipated per pulse on electroporated biomass is determined by the conditions for cooling the biomass in the electroporation cell. The device was tested on highly conductive green macroalgae from Ulva sp., a promising but challenging feedstock for the biorefinery. Successful electroporation was confirmed with bioimpedance measurements.Industrial relevanceSeaweed biomass is an emerging feedstock for biorefineries with already 30 million tons per year of global industrial production. However, most of the biomass produced today is lost. Pulsed electric field (PEF) extraction could allow saving energy on biomass drying, deashing and it could allow extracting various organic compounds. However, the parameters needed to seaweed biomass treatment with PEF are not known and will differ from species to species. Furthermore, very high salt content challenges most of the available laboratory PEF devices, limiting the ability for parameters optimization in the lab. The developed laboratory scale PEF system coupled to bioimpedance measurement provides a necessary set of tools and methods for PEF parameters optimization required for process scale-up.     

PEF-dependency on polyphenol extraction during maceration/fermentation of Grenache grapes

Application to different electric field strengths (E) and specific energies (W) with the pulsed electric fields (PEF) technology on the rate of extraction of phenolic compounds during maceration/fermentation of Grenache grapes was studied. A response surface model between the total polyphenol index extraction rate (TPI) and the E and W of the PEF treatments was established, which permitted the determination of PEF processing conditions to achieve a certain TPI. To achieve a TPI of 50, treatments ranged from high intensity and short time (8 kV·cm⁻¹ and 45 μs) to low intensity and long time (1 kV·cm⁻¹ and 2800 μs) applying an optimum W of 4 kJ·kg⁻¹ in all cases. The application of these PEF treatments reduced maceration time by a rate of 25 to 37% with respect to the untreated grape. Quality characteristics (color intensity, tannins, and total anthocyanins) were neither affected after fermentation nor after 12 months aging in bottles.     

Modelling the inactivation of Escherichia coli ATCC 25922 using pulsed electric field

Microbial tests were conducted to determine the effect of pulsed electric field treatment on microbial inactivation of gram negative Escherichia coli ATCC 25922 suspended in simulated milk ultra filtrate (SMUF). Kinetic analysis of microbial inactivation due to combined pulsed electric field (PEF) and thermal treatments of E. coli was investigated. A generalized correlation for the inactivation rate constant as a function of both electric field intensity and treatment temperature was derived. Comparison between experimental and theoretical variation of E. coli concentration with time after PEF treatment in a complete recirculation mode was conducted using the inactivation kinetics developed from the single pass measurements.

Industrial relevance

PEF technology has a tremendous potential to replace thermal pasteurisation for products which are sensitive to temperature. In this work a pulsed electric field process was mathematically modelled and a generalized correlation for the inactivation rate constant as a function of electric field intensity and treatment temperature was derived. The correlation is needed for the design of industrial PEF systems.     

Winery Trial on Application of Pulsed Electric Fields for Improving Vinification of Garnacha Grapes

The potential of pulsed electric fields (PEF) to improve polyphenol extraction during winemaking was investigated in a winery trial. Four thousand five hundred kilograms of Garnacha grapes were treated with PEF (4.3 kV/cm, 60 μs) at a flow of 1,900 kg/h using a collinear treatment chamber. Wine obtained from PEF-treated grapes with a maceration time of 7 days was compared with wines obtained from untreated and PEF-treated grapes with the current maceration time (14 days) used by the winery. After 7 days of maceration, the color intensity, anthocyanin content, and polyphenol index in the tank containing grapes treated by PEF were 12.5, 25, and 23.5 % higher, respectively, than in the tank containing untreated grapes. However, after 14 days of maceration, no significant differences were observed between the control wine and the wine obtained from grapes treated by PEF for these three indices. An HPLC analysis indicated that the concentrations of major individual phenolic compounds were similar among the three wines at bottling. A sensory analysis revealed that the wine obtained from PEF-treated grapes macerated for 7 days was significantly preferable to the other two wines.     

Critical Issues Pertaining to Application of Pulsed Electric Fields in Microbial Control and Quality of Processed Fruit Juices

Pasteurisation of fruit juices is normally carried out by thermal means. Heat treatment is an efficient technology for pasteurisation, but may also cause impairment of nutritive and sensory attributes. High-voltage pulsed electric field (PEF) treatment is a promising non-thermal processing method for pasteurisation of liquid foods. Sensory quality of fruit juices is important for consumers. PEF lends itself to be employed as an alternative to produce fruit juices of high quality and safe for consumption, and yet its practical application has been really limited. This paper reviews research carried out recently about the potential use of PEF to different fruit juices, aimed at employing the technology at industrial scale in order to search for wider commercialisation.     

高压脉冲电场处理对初榨橄榄油得率和品质的影响

为开发一种能提高初榨橄榄油(VOO)得率、对品质无不利影响且适用于工业化生产的新工艺,以甘肃陇南产区莱星、鄂植8号品种油橄榄鲜果为原料,采用高压脉冲电场(PEF)处理辅助传统工艺提取VOO,通过与传统提取工艺比较,研究PEF处理对VOO得率、理化性质、总多酚含量和脂肪酸组成及相对含量的影响。结果表明：与传统提取工艺相比,采用PEF处理VOO得率平均增幅为15.38%,果渣含油率平均降幅为22.28%,对VOO的色泽、酸值、过氧化值、总多酚含量和脂肪酸组成及相对含量等总体无显著性影响。研究认为,在VOO传统提取工艺的基础上,鲜果破碎之后增加PEF处理环节,可显著提高VOO得率,而且对VOO品质无不利影响,该技术在VOO工业化生产中有良好的应用潜力。     

Pilot scale inulin extraction from chicory roots assisted by pulsed electric fields

A pilot study for the pulsed electric fields (PEF) assisted countercurrent diffusion of inulin from chicory roots is presented. The influence of PEF parameters (electric field intensity E = 600 V cm^?1, treatment duration t_PEF = 10–50 ms) and diffusion temperature (varied between 30 and 80 °C) on soluble matter extraction kinetics, inulin content of juice, and pulp exhaustion are investigated. The draft (liquid to solid mass ratio) was fixed at 140%, similar to the industrial conditions. PEF treatment facilitates extraction of inulin at conventional diffusion temperature (70–80 °C), and diffusion temperature can even be reduced by 10–15 °C with comparable juice inulin concentration. Less energy consumption can be achieved by reducing PEF treatment duration to 10 ms, which is observed sufficient for effective extraction.     

Impact of air bubbles in a dielectric liquid when subjected to high field strengths

The dielectric breakdown of gas bubbles entrapped in liquid food flowing through the cavity of a pulsed electric field treatment chamber has been a limiting factor in this non-thermal food preservation technology. Prediction of electric field enhancement due to gas bubbles is an important tool in the design, modification, and optimization of the treatment chamber's electrode geometry and pressurization. Simulation of the electrostatic characteristics of a coaxial treatment chamber with specified voltage of 25 kV, filled with dielectric material with conductivity of 0.6 S/m containing gas bubbles, evidenced a significant perturbation in the electric field. The magnitude of electric fields generated inside the bubbles was almost two times higher than in the homogeneous food. Without pressurization (atmospheric conditions), the dielectric breakdown strength of the gas-filled bubbles was exceeded, thus indicating the risk of arcing. A system pressurization of approximately 8 atm could be sufficient to limit arcing when small gas bubbles (∼1 mm) are present. The presence of gas bubbles caused the field magnitude to decrease significantly near the boundary of the bubble, thus threatening the uniformity of the PEF treatment across the chamber gap. This perturbation in the electric field was more significant when more than one bubble was present or when smaller gaps were used. The dielectric breakdown threshold at a given pressure is more likely to be exceeded by bigger bubbles (>1 mm) entrapped in a fluid processed in smaller treatment chamber gaps (3 mm), than by smaller bubbles (<0.5 mm) in bigger gaps (5 mm). Simulations like those used in this research can be conducted to evaluate and optimize process homogeneity and safety, by studying the effects of different treatment chamber configurations, gaps, food products, number of gas-filled bubbles, or other suspended elements in the food.