Influence Of Pulsed Electric Field Research Articles

Drying Kinetics of Apple Tissue Treated by Pulsed Electric Field

The aim of this work was to study the influence of pulsed electric field (PEF) on the drying kinetics of apple tissue. Therefore, mathematical models that are commonly used in the literature were applied to describe the process. PEF treatment of the samples was carried out at an intensity of E = 5–10 kV/cm and 10–50 pulse numbers. Subsequently, the apples were convectively dried at 70°C and air velocity of 2 m/s. Based on electrical conductivity measurement, the cell disintegration index Z p was computed. Midilli et al.'s(Drying Technology, Vol. 20, pp. 1503–1513, 2001) model was evaluated as the most adequate to describe the moisture transfer in PEF-treated and intact samples. PEF pretreatment induced a reduction in drying time of up to 12% when 10 kV/cm and 50 pulses were applied. For instance, after 60 min of drying, the dimensionless moisture ratio for PEF-treated (10 kV/cm, 50 pulses) samples was 0.18 compared to 0.26 for the untreated apples. The effective moisture diffusivity, calculated on the basis of the Fick's second law, was 1.04 × 10−9 m/s for intact samples and from 1.09 × 10−9 to 1.25 × 10−9 m2/s for PEF-treated samples at 10 pulses at 5 kV/cm and 50 pulses at 10 kV/cm, respectively.

Improving the pressing extraction of polyphenols of orange peel by pulsed electric fields

Abstract The influence of pulsed electric field (PEF) treatment on the extraction by pressing of total polyphenols and flavonoids (naringin and hesperin) from orange peel was investigated. A treatment time of 60 μs (20 pulses of 3 μs) achieved the highest cell disintegration index ( Zp ) at the different electric field strengths tested. After 30 min of pressurization at 5 bars, the total polyphenol extraction yield (TPEY) increased 20%, 129%, 153% and 159% for orange peel PEF treated at 1, 3, 5 and 7 kV/cm, respectively. A PEF treatment of 5 kV/cm to the orange peels increased the quantity of naringin and hesperidin in the extract of 100 g of orange peels from 1 to 3.1 mg/100 g of fresh weigh (fw) orange peel and from 1.3 to 4.6 mg100 g fw orange peel respectively. Compared to the untreated sample, PEF treatments of 1, 3, 5 and 7 kV/cm increased the antioxidant activity of the extract 51%, 94%, 148% and 192%, respectively. The results of this investigation demonstrate the potential of PEF as a gentle technology to improve the extraction by pressing of polyphenols from fresh orange peel. This procedure enhances the antioxidant capacity of the extracts, reduces extraction times and does not require using organic solvents. Industrial relevance Processing of orange fruits to obtain fresh juice or citrus-based drinks generates very large amounts of byproduct wastes, such as peels that are a rich source of polyphenols mainly flavonoids. Extraction of these compounds from orange peels is a crucial step for use of these compounds in the food and pharmaceutical industries as antioxidants. PEF-assisted extraction by pressing of polyphenols from fresh orange peels stands as an economical and environmentally friendly alternative to conventional extraction methods which require the product to be dried, use large amounts of organic solvents and need long extraction times.

Pulsed-electric-field-assisted extraction of anthocyanins from purple-fleshed potato

The influence of pulsed electric field (PEF) treatment on the anthocyanin extraction yield (AEY) from purple-fleshed potato (PFP) at different extraction times (60–480min) and temperatures (10–40°C) using water and ethanol (48% and 96%) as solvents has been investigated. Response surface methodology was used to determine optimal PEF treatment and optimise anthocyanin extraction. A PEF treatment of 3.4kV/cm and 105μs (35 pulses of 3μs) resulted in the highest cell disintegration index (Zp=1) at the lowest specific energy requirements (8.92kJ/kg). This PEF treatment increased the AEY, the effect being higher at lower extraction temperature with water as solvent. After 480min at 40°C, the AEY obtained for the untreated sample using 96% ethanol as the solvent (63.9mg/100g fw) was similar to that obtained in the PEF-treated sample using water (65.8mg/100g fw). Therefore, PEF was possible with water, a more environmental-friendly solvent than ethanol, without decreasing the AEY from PFP.

The influence of pulsed electric field on hematological parameters in rat

The aim of the present study is to investigate whether or not pulsed electric field (PEF) affects some hematological parameters in rats. Sixteen healthy male Wistar rats weighting 150-200 g were used and were randomly divided into two groups. Exposure group (n = 8) was exposed to a PEF (10 kV m⁻¹ for 1 h d⁻¹) for 10 consecutive days. The control group rats (n = 8) were not exposed to PEF. The following hematological parameters were measured in both the groups: white blood cells (WBCs), red blood cells (RBCs), hemoglobin (Hb), hematocrit (Ht) and platelets (PLTs). Some of the hematological parameters under investigation were similar in both the groups. Exposure group, exposed for 1 h d⁻¹ during 10 consecutive days, induced a significant increase in the rates of WBC (p < 0.05), RBC (p < 0.05), Hb (p < 0.05), Ht (p < 0.05) and PLTs (p < 0.05) in blood when compared with control. These results suggest that PEFs affect the hematological parameters in rat. Results of the parameters are statistically significant.

Acid Tolerance of &amp;lt;i&amp;gt;Lactobacillus acidophilus&amp;lt;/i&amp;gt; LA-K as Influenced by Various Pulsed Electric Field Conditions

Pulsed electric field (PEF) processing involves the application of pulses of voltage for less than one second to fluid foods placed between two electrodes. Lactobacillus acidophilus is an important probiotic bacterium used for the production of fermented dairy products. Acid tolerance is an important probiotic characteristic. The influence of PEF on acid tolerance of Lactobacillus acidophilus is not known. Objective of this study was to elucidate the influence of certain PEF conditions on the acid tolerance of Lactobacillus acidophilus LA-K. Freshly thawed Lactobacillus acidophilus LA-K was suspended in sterile peptone 0.1% w/v distilled water and treated in a pilot plant PEF system. The treatments were pulse width (3, 6 and 9 μs), pulse period (10,000; 20,000 and 30,000 μs) and voltage (5, 15 and 25 kV/cm). Control was run through PEF system at 60 mL/min without receiving any pulsed electric field condition. Data were analyzed using the PROC GLM of the Statistical Analysis Systems (SAS). Differences of least square means were used to determine significant differences at P Lactobacillus acidophilus LA-K lowered by increasing pulse widths and voltages but lowering pulse periods.

Influence of pulsed electric field on growths of soil bacteria and pepper plant

DC 20 volt of electricity was charged to the electrodes placed around hot pepper plants to induce electrical redox reaction. Anode and cathode were periodically exchanged at intervals of 30 seconds to develop a pulsed electric field (PEF), by which the ORP of the soil around the pepper plant roots were fluctuated from 17 to −13 volts. Mean viable cell number of the intrinsic bacteria in five different positions was variable from 77,000 to 396,000 around electrodes and 339,000 to 680,000 around plants in the PEF, and 538,000 to 927,000 around plants in the conventional field. The mean viable cell number of the extrinsic bacteria (R. solanacearum) in five different positions was variable from 15,000 to 47,000 around electrode and 152,000 to 374,000 around plant in the PEF, and 294,000 to 607,000 around plants in the conventional field. Mean 3.93 and 5.67 of hot pepper plants were infected with bacterial wilt every two days by passive and active infection, respectively, in the conventional field. Mean 1.25 and 2.5 of hot pepper plants were infected with bacterial wilt every two days by passive and active infection, respectively, in the PEF. Mean sprouting number of seeds in the PEF and conventional field and was 45.0 and 48.2, respectively. Mean dry weight of hot pepper plants was 3.15 g and 2.51 g in the PEF and conventional field, respectively. The TGGE band pattern in the PEF was not very different in comparison with that in the conventional field (B and D) based on the band number, which corresponds to the bacterial diversity. This study suggests that the PEF would be functioning as an environmental factor to inhibit bacterial growth rather than to be a physical agent to destroy bacterial cells.

Influence of pulsed electric field energy on the damage degree in alfalfa tissue

The objectives of this study were to investigate the influence of pulsed electric field (PEF) parameters on the damage degree of alfalfa mash, and to determine the relationship between the maximum damage degree and the energy used. Alfalfa mash was treated with PEF at various electric field strengths of 1.25, 1.90, and 2.50 kV/cm. The capacitance of the discharge capacitor was varied from 0.5 to 1.5 μF in steps of 0.5 μF. The pulse number was increased gradually to the point where the impedance became constant. There was no significant increase in the rate of damage beyond 0.5 kJ applied energy. The rate of change of the damage degree at 0.5 kJ was highest when the capacitance was 1.5 μF for all the voltages. Increase in the electric field strength led to decrease in energy needed to obtain the maximum damage degree. To achieve an efficient result for alfalfa juice extraction, the capacitance of the discharge capacitor should preferably be 1 μF or more. In order to minimize energy consumption for a given damage degree in alfalfa, it is desirable to have the highest energy per pulse and fewer number of pulses.

Effect of Pulsed Electric Field and Osmotic Dehydration Pretreatment on the Convective Drying of Carrot Tissue

The influence of pulsed electric field (PEF) and subsequent centrifugal osmotic dehydration (OD) on the convective drying behavior of carrot is investigated. The PEF was carried out at an intensity of E = 0.60 kV/cm and a treatment duration of t PEF = 50 ms. The following centrifugal OD was performed in a sucrose solution of 65% (w/w) at 40°C for 0, 1, 2, or 4 h under 2400 × g. The drying was performed after the centrifugal OD for temperatures 40–60°C and at constant air rate (6 m3/h). With the increase of OD duration the air drying time is reduced spectacularly. The dimensionless moisture ratio Xr = 0.1 is reached for PEF-untreated carrots after 370 min of air drying at 60°C in absence of centrifugal OD against 90 min of air drying after the 240 min of centrifugal OD. The PEF treatment reduces additionally the air drying time. The total time of dehydration operations can be shortened when OD time is optimized. For instance, the minimal time required to dehydrate untreated carrots until Xr = 0.1 is 260 min (120 min of OD at 40°C and 140 min of drying at 60°C). It is reduced to 230 min with PEF-treated carrots. The moisture effective diffusivity D eff is calculated for the convective air drying based on Fick's law. The centrifugal OD pretreatment increases drastically the value of D eff . For instance, 4 h of centrifugal OD permitted increasing the value of D eff from 0.93 · 10−9 to 3.85 · 10−9 m2/s for untreated carrots and from 1.17 · 10−9 to 5.10 · 10−9 m2/s for PEF-treated carrots.

Application of relaxation periods during electrodialysis of a casein solution: Impact on anion-exchange membrane fouling

Electrodialysis (ED) is a membrane process used on a large scale. However, one of the common problems is fouling of ion-exchange membranes stacked in the cell. The use of pulsed power, consisting in applying a constant current density during a fixed time of application ( T on) followed by a pause duration ( T off), was demonstrated recently as an effective fouling mitigation method for electrodialysis. Up until now, no work has investigated the potential of electrodialysis using pulsed electric field on protein fouling. The aim of the present work was to study the influence of pulsed electric field (PEF) with a low frequency square shaped periodic signal ( T on = 10 s– T off = 10 s, T on = 10 s– T off = 40 s) in comparison with dc current during electrodialysis of a casein solution at different current densities (10, 20 and 30 mA/cm 2) on membrane fouling. It appeared from these results that PEF, under certain conditions of pulse, would avoid fouling on anion-exchange membranes. For 10 s–40 s pulsed electric field conditions, no fouling was observed with any density, while for 10 s–10 s PEF conditions, fouling appeared only at current density over 10 mA/cm 2. dc current, whatever the current density conditions, led to a fouling on the diluate side of the AEM. Furthermore, when fouling occurred, magnitude layer thickness and dry weight increased with the applied current density. The nature of the fouling was identified as 97% protein. The protein fouling would be due to the dissociation of water molecules and/or heat increase at the anion-exchange membrane interface. The relaxation time of the pulse would limit both phenomena on the membrane.

Influence of pulsed electric field on various enzyme activities

Effects of high-voltage pulsed electric field (PEF) on native or thermal denatured enzyme activities were studied. When PEF was applied to various native enzymes, 105–120% of initial enzyme activities were observed after PEF treatment. It was suggested that an activation of enzyme would be possible by PEF treatment. We attempted a refolding of thermal denatured enzyme by using PEF. When PEF was applied to denatured peroxidase, enzyme refolding was accelerated in PEF and 60% of initial activity was observed after 12 kV/cm and 30 s of PEF treatment although spontaneous refolding of this enzyme resulted in 40% of initial activity. On the other hand, when PEF was applied to thermal denatured lactate dehydrogenase (LDH), further PEF-induced inactivation was observed. It was suggested that the influence of PEF is dependent on the type of enzyme.

Pulsed electric field enhanced drying of potato tissue

The influence of pulsed electric field (PEF) treatment on convective drying of potato tissue was investigated. The drying experiments for potato disks were done in the interval of drying temperatures 30–70 °C. The effects of pre-treatment before drying and PEF treatment in the course of the drying are discussed. The temperature dependencies of moisture effective diffusion coefficient D eff for intact, PEF-treated and freeze-thawed potato tissues are compared. It is shown that D eff is a function of the conductivity disintegration index Z σ . The moisture effective diffusion coefficient D eff is sensitive to the pre-treatment procedure, and the highest values of D eff are always observed for freeze-thawed pretreated samples. The data show that thermal pre-treatment of samples at high temperatures ( T = 70 °C) has practically no beneficial effect on the drying rate, though the same thermal pre-treatment at mild temperatures ( T = 50 °C) increases the moisture effective diffusion coefficient D eff and gives an effect that is comparable with that for the PEF pre-treated samples.

Constant Rate Expressing of Juice from Biological Tissue Enhanced by Pulsed Electric Field

Pulsed electric field (PEF) is an innovative technology, which can be successfully combined with solid/liquid expressing of juice from biological materials. The fresh juicy plants contain the juice in closed cells. The application of PEF ensures the electropermeabilization of cellular membranes, which facilitates the expulsion of liquid from the interior of cells. This article describes the influence of PEF on the kinetics of juice extraction from the layer of sugar beet particles expressed at a constant rate. Experimental study was carried out using a laboratory filter-press cell connected to a PEF treatment system. The PEF was applied by two different modes: as a pretreatment operation before pressing and as a treatment during pressing. The application of PEF to nonpressurized cake leads to increase of energy consumption and higher applied voltage. The PEF treatment of excessively pressurized cakes enhances the juice yield; however, the expressing of juice is significantly delayed. The best result is obtained when the sugar beet tissue is treated with PEF at 1.5–5 bars. The influence of PEF parameters on the juice yield was also studied. The intensity of PEF was varied from 0 to 1000 V/cm and the number of pulses was varied between 0 and 1000. It was established that the optimal parameters of PEF after the cake pressurization at 5 bar were in the next range: intensity of PEF E = 500 V/cm and duration of PEF application 0.03–0.05 s.

Pulsed electric field treatment of apple tissue during compression for juice extraction

The influence of pulsed electric field (PEF) simultaneous to pressure treatment on juice expression from fine-cut apple raw material has been investigated. Dependencies of specific conductivity σ, juice yield Y, instantaneous flow rate v and qualitative juice characteristics at different modes of PEF treatment are discussed. Three main compression phases were observed in a case of mechanical expression. A unified approach is proposed for juice yield data analysis allowing a reduction in data scattering caused by differences in the quality of samples. Simultaneous application of pressure and PEF treatment revealed a passive form of PEF-induced cell plasmolysis. Pressure provokes the damage of defect cells, enhances diffusion migration of moisture and depresses the cell resealing processes. PEF application at the moment when the press-cake's specific electrical conductivity reaches a minimum and the pressure achieves its constant value seemed to be the most optimal. It has been found that a combination of pressing and PEF treatment gives the optimum results and enhances the yield of juice significantly and improves its quality.

Decomposition of nucleic acid molecules in pulsed electric field and its release from recombinantEscherichia coli

The influence of pulsed electric field (PEF) on chromosomal DNA, plasmid DNA, and RNA molecules was studied. It was confirmed that chromosomal DNA and RNA were decomposed to smaller size or disappeared in PEF because of observations on agarose gel electrophoresis of nucleic acid molecules before and after PEF treatment. However, supercoiled form of plasmid DNA was relatively stable in electric conditions when other nucleic acid molecules containing liner and opened circle forms of plasmid DNA were decomposed. We also studied a release of nucleic acid molecules from recombinantE. coli in PEF to improve a method of plasmid DNA preparation. Although some kinds of nucleic acid molecules were released by PEF treatment, a purification of plasmid DNA was impossible at any condition used in this study. The extraction of nucleic acid molecules by using PEF could be performed within 1 min, that was shorter period than that of ordinary method.