Moderate Electric Field Treatment Research Articles

Production of iron-enriched kale leaves (Brassica oleracea L. var. acephala) utilizing combinations of novel food processing technologies

Despite its rich content, iron bioavailability from leafy greens is low relative to protoporphyrin-bound (e.g. heme) iron, richest in red meat. We hypothesized that combinations of novel food processing techniques, i.e., vacuum impregnation (VI), water-bath (WB), overnight immersion (IM) in an iron sulfate solution, and moderate electric field (MEF) could improve kale leaf iron content and produce protoporphyrin-bound iron derivatives in situ. Combination MEF treatments increased leaf iron concentrations ∼160x greater than control. A ferroprotoporphyrin IX isomer was detected in MEF and IM-treated kale, providing up to 0.75 mg protoporphyrin-bound iron/100 g kale leaf fresh weight (FW). IM and MEF treatments also significantly increased leaf total chlorophyll concentrations ∼3x greater than the control. The novel food processing techniques employed herein produced kale with significantly higher concentrations of free + heme-bound iron, as well as total chlorophyll, relative to other plant-based sources. Future testing will determine if this “iron-enhanced” kale delivers more iron, as compared to other iron-rich food sources.

Effects of electric field intensity regulation on protein aggregation behaviour and foaming property of soybean 7S globulin

In this study, the aggregation behaviour of soybean 7S globulin after moderate electric field (MEF) treatment was investigated, and the influence of the electric field and temperature field on the structure and foaming property of the aggregates were analysed and compared with conventional water bath (COV). The results showed that MEF treatment enhanced the properties of the aggregates. The properties of the treated aggregates were significantly better than those of native 7S globulin. At an electric field strength of 8 V/cm, the solubility, turbidity, and particle size increased from 95.81 % to 99.37 %, 0.097 to 0.189 and 61.97 nm to 113.21 nm, respectively, and the absolute value of potential decreased from 23.56 mV to 22.12 mV. The SDS-PAGE and size exclusion chromatography (SEC) results showed that the electric field had a positive effect on the aggregate formation of the Fourier-transform infrared spectroscopy (FTIR), fluorescence spectroscopy, surface hydrophobicity (H0) and total sulfhydryl (SHT) results indicated that the spatial structure of the protein was changed by MEF treatment. The protein β-sheet content was reduced, and the Try that was originally buried inside the molecule was exposed, resulting in an increase in H0 and a decrease in SHT. The foaming property of the 7S globulin aggregates was improved by MEF treatment.

Nonthermal inactivation effects on oxidative enzymes in grape juice influenced by moderate electric fields: Effect of constant exposure electrical treatments combined with temperature

Inactivation of polyphenol oxidase (PPO) and peroxidase (POD) enzymes in fresh grape juice was studied by subjecting the juice to moderate electric field (MEF) treatments of 82 and 87 V/cm field strengths. We used an electro-processing device that was built to minimize ohmic heating and enhance cooling during application of electric fields. Kinetic studies indicate that the MEF treatments increase the inactivation of both enzymes at 65 and 75 °C, compared to the corresponding control treatments without electric fields. The increase in the inactivation becomes statistically significant ( P ≤ 0.05) in the MEF treatment at 75 °C. Molecular motion simulations of PPO and POD enzymes correlate with the experimental results. The study results further indicate the efficacy of MEF treatments on the nonthermal inactivation of enzymes, which are held at or near their thermal inactivation threshold temperatures (≤80 °C for PPO and POD). • Moderate electric field (MEF) treatments inactivate enzymes (PPO, POD) in grapes. • The efficacy of MEFs increases with increasing field strength and temperature. • The thermal impact on grape juice can be reduced by applying MEF treatments. • Enzyme's thermal inactivation threshold temperature is useful in MEF studies. • Thermostability and electric field sensitivity of enzymes affect the inactivation.

Effects of moderate electric field on the structural properties and aggregation characteristics of soybean protein isolate

The effects of moderate electric field (MEF) at different intensities (4–10 V/cm) on the structural properties and aggregation characteristics of soybean protein isolate (SPI) during ohmic heating (OH) were investigated. Fourier-transform infrared spectroscopy, fluorescence spectroscopy, and analysis of surface hydrophobicity and total free sulfhydryl groups showed that MEF treatments at 4 and 6 V/cm facilitated the unfolding of the protein structure, thus exposing more hydrophobic residues and enhancing surface hydrophobicity. Protein aggregation increased with the increase in electric field intensity, as demonstrated by the turbidity and particle size measurements, size exclusion chromatography, and atomic force microscopy. MEF treatments at 8 and 10 V/cm induced the formation of large, soluble aggregates dominated by disulfide bonds and hydrophobic interactions. Rheological analysis showed that the MEF treatments at 4 and 6 V/cm improved the gelation capacity. These results contribute to improving the understanding of the changes in structure and aggregation properties of SPI during MEF treatment and create opportunities to modify protein structure by MEF technology. • The moderate electric field (MEF) changed SPI structure and induced aggregation. • Changes of structure and aggregates were affected by electric field intensity (EFI). • Lower EFI induced SPI unfolding to form smaller and uniformly distributed aggregates. • Higher EFI resulted in larger aggregates and higher degree of protein denaturation.

Changes in the structural and catalytic characteristics of α-amylase under moderate electric field

The study aimed to investigate the effect of moderate electric field (MEF) on the performance of α-amylase in corn starch hydrolysis. MEF (1–12.5 V/cm, 50–350 Hz) was performed on α-amylase and/or corn starch under different conditions (0–50 mM Ca 2+ ; 40–70 °C; 10–120 min). As a pretreatment, low-intensity MEF (2.5 V/cm) did not induce the hydrolysis of native and fully gelatinized starch but increased the enzyme activity by 23% due to slight unfolding of α-amylase. Although more extensive hydrolysis was observed for fully gelatinized starch when the hydrolysis was performed by MEF-pretreated α-amylase (reducing sugar: 38.5 g/L, the control; 48.6 g/L, 2.5 V/cm; 51.2 g/L, 2.5 V/cm + 10 mM Ca 2+ ) and MEF treatment in the presence of α-amylase (42.2 g/L, the control; 48.1 g/L, 2.5 V/cm; 51.3 g/L, 2.5 V/cm + 10 mM Ca 2+ ), a small increase occurred for native starch. Overall, the results proved that substrate structure dominated in the enzymatic hydrolysis of starch under MEF, providing a guide for applying electro-based techniques in starch modification. • Low-intensity moderate electric field (MEF) improved the activity of α-amylase. • Enhanced enzyme activity was attributed to the changed conformation structure. • Densely packed structure of starch dominated in MEF-assisted enzymatic hydrolysis. • Extensive hydrolysis occurred for fully gelatinized starch under MEF. • Minor hydrolysis happened for native starch under MEF.

Nonthermal inactivation of polyphenol oxidase in apple juice influenced by moderate electric fields: Effects of periodic on-off and constant exposure electrical treatments

Inactivation of polyphenol oxidase (PPO) in fresh apple juice was studied in moderate electric field (MEF) treatments at field strengths in the range of 85–110 V/cm. The apple juice was subjected to periodic on-off treatments at 50 °C and constant exposure MEF treatments at 50 and 65 °C using two different electro-processing devices, specially constructed for the purpose. PPO inactivation by the electric fields was determined with respect to the corresponding control (nofield) treatments. The application of periodic on-off treatments resulted in about 100% increase (P ≤ 0.05) of the thermal inactivation rate constant of PPO at 50 °C. A similar relative increase of the thermal inactivation rate constant was observed with the constant exposure MEF treatment at 50 °C. The electric field influence was improved significantly (P ≤ 0.05) in the constant exposure MEF treatment at 65 °C. Differences in electrical energy input among the MEF treatments were observed. Results indicate both the electric field strength and the treatment temperature play critical roles in enzyme inactivation by moderate electric fields. Industrial relevanceThis study shows polyphenol oxidase enzyme in fresh apple juice can be significantly inactivated by moderate electric fields applied at below thermal pasteurization temperatures. Therefore, moderate electric field treatment applications are beneficial for the minimally processed fruit and vegetable industry.

Improving the Extraction of Juice and Bioactive Compounds from Blueberry Fruits and Their By-products by Application of Moderate Electric Field (mef)

The influence of Moderate Electric Field (MEF) pre-treatment of blueberry fruits on the yield and quality of the expressed juice as well as the subsequent extraction yield of bioactive compounds from berry by-products (press cake left after MEF-assisted pressing), was investigated. Thermal MEF pre-treatments were performed under different combinations of electric field strengths (E=18-55 V.cm-1) and final heating temperature (Tf=25-80 °C) before applying a pressure of 1.32 bar for 5 min. For the sake of comparison, the effect of conventional heating (CH) (Tf=25-80 °C), was also investigated. Results showed that the Zp values increased with increasing the field strength and heating temperature. However, at the same final heating temperature, MEF treatment achieved higher Zp values (up to 0.66) than CH (up to 0.45). Coherently, thermal MEF pre-treatment (36.4 V.cm-1, 60 °C) significantly increased the juice yield, which also showed higher TPC, TAC, and AA, as compared with either untreated or CH-treated samples. Moreover, compared to the untreated and CH-treated samples, higher amounts of total phenolics, total anthocyanins and antioxidant activity were detected in the press cake extracts. These results were explained by the combined non-thermal and thermal effect of MEF on the cell disintegration and extraction efficiency.

Effect of moderate electric field on structural and thermo-physical properties of sunflower protein and sodium caseinate

Moderate electric field (MEF) was employed to sunflower protein isolate (SPI) and sodium caseinate (CAS) to change their structural and thermo-physical properties with a non-thermal approach. MEF treatment significantly reduced the average particle size with noticeable changes in the uniformity of SPI and CAS solutions. A maximum of 10% reduction in the surface tension was observed for 0.2% w/w SPI sample by applying 150 V for 20 s. This effect was less pronounced for CAS samples and for the protein concentration of 2% w/w. FTIR spectra provided an increased α-helix content for SPI inducing a bulkier, loosened and more hydrophilic structure which is unlikely for CAS. Intrinsic Fluorescence Spectroscopy revealed that MEF treatments changed the tertiary structures of SPI and CAS. Denaturation temperatures and enthalpies of the SPI and CAS samples were decreased by MEF treatments.

Moderate electric field pasteurization of milk in a continuous flow unit: Effects of process parameters, energy consumption, and shelf-life determination

This study presents a new non-thermal moderate electric field (MEF) process for milk pasteurization. To evaluate the applicability of this process, fresh milk was treated by MEF at electrical field strength (EFS) of 8.33, 14.58, and 20.80 V/cm and mass flow rates (MFR) of 0.018, 0.042 and 0.077 kg/s to compare the microbiological quality, alkaline phosphatase activity, chemical composition, and some physical properties of the product with those of conventionally pasteurized (15 s at 72 °C) and raw milk. The changes in the total count of bacteria (TCB) and titratable acidity of samples were observed during 18 days of storage at 5 °C for shelf-life estimation. The results showed that MEF reduced energy consumption by 63% in comparison with thermal pasteurization. Also, MEF treatment inactivated coliforms (100%), Staphylococcus aureus (100%), psychrophiles (100%), yeasts and molds (100%), and alkaline phosphatase (100%) while keeping the processing temperature below 22 °C. Also, TCB of sample was reduced by increasing the EFS from 8.33 to 20.8 V/cm and decreasing the MFR from 0.0774 to 0.0185 kg/s. The longest shelf-life of MEF samples, i.e., 15 days, was observed at EFS of 20.80 V/cm and MFR of 0.018 kg/s which was better than that of thermal pasteurization samples, i.e., 9 days.

Preparation of porous starch by α-amylase-catalyzed hydrolysis under a moderate electric field

Enzymatically-catalytic conversion of starch-based industrial waste into porous materials was enhanced by a moderate electric field (MEF). Changes in the hydrolysis rate, α-amylase activity and starch structure during MEF treatment (0–20 V, 0–400 Hz, room temperature and 0–2 h) were monitored and the hydrolyzed products were characterized by scanning electron microscopy, X-ray diffraction and water/oil adsorption analyses. The results showed that MEF enhanced enzymatic hydrolysis mainly by destroying starch structure, rather than by altering α-amylase activity. The average number of pores of hydrolyzed starch increased when voltage increased from 2 to 15 V, but a further increase of voltage caused the gelatinization of starch, thus making it unfavorable for the preparation of porous materials. The crystallinity of electrically-treated porous starches was decreased by 2.87–5.06%. The water and oil adsorption capacity of the porous starches was much higher than that of their native counterpart. Overall, this study extends the applications of electric field-based techniques in an enzymatic modification of biomaterials.

Moderate Electric Field Treatment Enhances Enzymatic Hydrolysis of Cellulose at Below-Optimal Temperatures

Saccharification of cellulosic biomass for the fermentation of transportation fuels faces several challenges. Cellulose is highly stable, and even with enzymatic assistance, decomposition of cellulose is slow. Additionally, the enzymes are expensive and sensitive to thermal and mechanical inactivation. In this work, we studied the effects of moderate electric field (MEF, in the range from 1 to 1000 V per cm) treatments on the effectiveness of enzymatic saccharification. MEF treatments were applied to determine their effects on enzyme activity. We considered the effects of field strength, frequency, application regime and temperature. It was found that the enzyme responded to alterations in the frequency of the waveform, with 50 to 60 Hz maximizing the effects of the field, although the effects of field strength and application regime were more significant. It was found that the electric field could have a positive, negative, or negligible effect depending on the field strength. Most notably, when MEF treatments were applied over a range of temperatures, it was found that MEF treatment significantly improved enzyme activity at lower temperatures, leading to the observation that MEF treatment imitates a temperature increase. Calculations simulating the electrophoretic motion of the enzymes verified that the magnitude of motion associated with the MEF treatments was qualitatively similar to the change in molecular motion associated with temperature increases.

Effect of moderate electric field pretreatment in combination with ozonation on inactivation of Escherichia coli K12 in intact shell eggs

A currently investigated decontamination process for intact shell eggs involves mild water bath heat treatment followed by ozonation. We investigated the effect of a Moderate Electric Field (MEF) applied during water bath pretreatment on the survival of Escherichia coli K12 (a common Salmonella surrogate for heat processing), inoculated in the albumen. Results showed the addition of an electric field significantly improved (p < 0.05) the decontamination process lowering population by an extra 0.94 log CFU/g compared to the conventional heating process when plated on Sorbitol MacConkey Agar (SMAC), despite the temperatures during the MEF process being slightly lower than the conventional process. Follow-up studies suggest that small currents do flow through the eggs during MEF treatment, explaining the additional lethal effect. Our results suggest that temperatures for egg treatment could be reduced during a MEF inactivation process, resulting in potential quality improvement.

Application of a moderate electric field for the potential acceleration of the salting process of Atlantic salmon (Salmo salar)

AbstractThe aim of this research was to investigate the acceleration of brine‐salting process of salmon when coupling it with moderate electric field (MEF). Salmon samples were cut into cylinder shape (0.025 ± 0.001 m diameter and 0.025 ± 0.001 m height), and then brined at two salt concentrations (6 or 24%) until equilibrium is reached. Processing time, salt concentration throughout time, moisture content, color, and hardness of salmon samples were determined. The results showed that the effective diffusion coefficients (De) of salt within salmon tissue, were in the range 3.28 × 10−10 to 4.22 × 10−10 m2/s for both standard process and coupled with MEF, without significant differences (p &gt; .05). Even though De had no significant differences for both processes, processing time for MEF treatments were significantly shorter, due to differences in the equilibrium salt concentration. Also, MEF did not affect quality parameters when compared with standard process. In addition, MEF treatments showed an increased salt concentration in the final product.Practical applicationsOne of the most attractive technologies to add value to Atlantic salmon is the cold smoking process. For this purpose, salting is considered as the main step during cold smoking of Atlantic salmon to extend its shelf‐life. However, salmon salting using a brining solution take many hours until reaching an adequate salt concentration (between 2.0 and 3.9% or 3.5 and 6% in the water phase). The moderate electric field (MEF) technology will allow to reduce the salting processing time up to 80% using a very low electric field (around 2 V/cm) and without affecting the final quality of the product, compared with the traditional method. This technology shows potential for a successful implementation in the seafood industry without requiring a high investment cost.

Extraction from Food and Natural Products by Moderate Electric Field: Mechanisms, Benefits, and Potential Industrial Applications.

Several extraction techniques have been proposed recently as the food industry is seeking alternatives to tedious classical methods. Moderate electric field (MEF) extraction at low and high temperatures offers several advantages such as enhancing product quantity and quality as well as saving time and energy. This method has gained interest as a preferred extraction technique among researchers. This review is devoted to introducing the principles, mechanisms, and recent progress in the MEF extraction technique. The parameters influencing MEF treatment are also discussed and performances are compared to conventional extraction methods. Considerations for industrial development of MEF as well as its drawbacks are also discussed. MEF extraction is applicable to a wide range of food materials and offers several benefits such as reducing extraction time and energy and also enhancing the extract's quality and yield. Optimizing process parameters, such as treatment time and temperature, electric field intensity, and frequency, along with raw material selection and preparation can boost the performance of a MEF system. Further investigations on safety and sustainability of this novel technique are required prior to commercial applications.

Effects of controlled-frequency moderate electric fields on pectin methylesterase and polygalacturonase activities in tomato homogenate

The effect of controlled-frequency moderate electric field treatments on pectin methylesterase and polygalcturonase activities in tomato homogenate was investigated by subjecting identically treated control and electrically-treated samples to the same temperature history. Additionally, a model was developed for the motion of the enzyme molecules subjected to an electric field. Results show that the application of electric fields at a low field strength (0.4V/cm) constant temperature (65°C) has a statistically significant effect on pectin methylesterase activity, typically at or lower than 60Hz. At higher frequencies, the effects are negligible. Molecular motion simulations suggest that the efficacy at low frequencies may be due to the amplitude of motion being of the order of the intermolecular distance for water. Higher frequencies result in small overall displacements due to rapid reversals in the direction of motion.

Influence of moderate electric fields on gelation of whey protein isolate

Proteins are one of the food constituents most affected by heating, and some of the changes involve their unfolding, denaturation and gelation. Ohmic heating has often been claimed to improve the quality of foodstuffs due to its uniform heating and (putative) presence of a moderate electric field (MEF). However, this is still subject to discussion, so it is important to determine the effect of ohmic heating and of its MEF upon food constituents. Hence, the aim of this work was to evaluate the effects of MEF on denaturation, aggregation and viscoelastic properties of whey protein isolate (WPI), and compare them with those obtained via conventional heating under identical treatment conditions (up to 30 min at 85 °C). Results have shown that MEF interferes with whey protein unfolding and aggregation pathways at relatively high temperatures. MEF treatments have resulted in WPI solutions possessing more 8 and 10% of native β-Lactoglobulin and α-Lactalbumin, respectively, after 30 s of heating at 85 °C, when compared with a conventional heating method. Protein aggregates from MEF-treated WPI solutions presented a maximum increase in size of 78 nm, whereas conventional heating produced an increase of 86 nm. Unlike in conventional heating, aggregation of whey proteins during MEF was not sufficiently strong to form a true elastic gel network, since decreases in both storage and loss modulus were observed following MEF treatment. Our results suggest that MEF may provide a novel method for production of a whey protein matrix with distinctive gel-forming properties.

Changes in permeability of moderate electric field (MEF) treated vegetable tissue over time

Abstract A microscopic examination of beet tissue given a moderate electric field treatment shows that some cells lose their membrane selectivity while others remain intact. Raw, thawed, or precooked potato cylinders were chilled, and then warmed to 25 °C by either allowing them to equilibrate or by MEF treatment. The conductivity from 100 Hz to 20 kHz and apparent dielectric constant from 100 Hz to 5 kHz was initially not significantly different between raw-untreated samples and raw-MEF treated samples, but over 24 h, that of the raw-MEF treated samples increased while that of the raw-untreated samples remained constant. No such distinct pattern emerged from the thawed or precooked samples. The apparent dielectric constant of raw-MEF treated potato above 5 kHz was not significantly different from raw-untreated potato and higher than thawed and precooked potato. None of the samples showed marked changes in dielectric constant at 5–20 kHz over the 24 hour period. Apparently, even mild electrical treatments permeabilize vegetable tissue, permitting enhanced diffusion. This work has implications in improving nonthermal permeabilization processes for eukaryotic cells, which can be used in fruit and vegetable drying and juice extraction operations.

Effect of moderate electric field frequency and growth stage on the cell membrane permeability of Lactobacillus acidophilus

Changes in growth kinetics and metabolic activity of microorganisms under the presence of a moderate electric field (MEF) have been hypothesized as being due to temporary permeabilization of cell membranes. We investigated herein the effects of frequency and growth stage on cell membrane permeabilization of Lactobacillus acidophilus OSU 133 during MEF fermentation. Cells were stained with two fluorescent nucleic acid stains: the green, nonselective, cell membrane permeable SYTO 9, and the red, cell membrane impermeable propidium iodide (PI). Fluorescence exhibition post-treatment was assessed using fluorescence microscopy. Total plate counting was done to determine whether or not the permeabilized population represented live cells. Fermentation treatments investigated were conventional (control) and MEF (2 V/cm, 45, 60, 1,000, 10,000 Hz) at 30 degrees C. Studies were conducted at 45 Hz for lag, exponential, and stationary phases of growth. Low frequency MEF treated cells exhibited significantly greater numbers of red cell counts than conventional treatments; further, no significant differences existed in viable counts between MEF and conventional treatments, suggesting that the red counts represent permeabilized live cells. MEF treatments at the early stage of bacterial growth at 45 Hz exhibited the maximum permeabilization followed by treatments at 60 Hz. MEF treated samples at frequencies higher than 60 Hz did not exhibit red fluorescence. Cells at lag phase showed the greatest susceptibility to permeabilization followed by those at exponential phase. No evidence of electroporation was observed during the stationary phase. To our knowledge, these observations provide the first evidence that cell membrane permeabilization occurs under the presence of electric fields as low as those under MEF.

Moderate Electric Field Treatment of Sugarbeet Tissues

The effects of thermal and moderate electric field (MEF) treatment on the damage of sugarbeet tissue were discussed. The activation energy ΔUT was estimated as 170 kJ mol−1 using the temperature dependences of the characteristic thermal damage time within the temperature interval 50–70 °C. The temperature dependences of electrical conductivity were measured for the maximally damaged and intact sugarbeet tissues; these data were used for estimation of the conductivity disintegration index at different MEF treatments. The results evidenced that the electrically stimulated damage of a sugarbeet tissue occurs even at a rather small electric field strength E of 20 V cm−1 if treatment time is large enough (t≈1 h). The energy consumption caused by MEF-treatment is mainly related to temperature elevation inside the tissue and noticeably decreases with increasing electric field strength E. MEF-treatment experiments in the aqueous media reveal the dependence of damage efficiency on sample orientation with respect to the external electric field.

Extraction Using Moderate Electric Fields

ABSTRACT: During moderate electric field (MEF) processing, a voltage applied across a food material may affect the permeability of cell membranes. It is known that high electric fields can cause either reversible or irreversible rupture of cell membranes. In this research, the effect of MEF processing on permeability was studied. Effects of frequency and electric field strength were investigated. Cellular structure was investigated by transmission electron microscopy (TEM). Fermented black tea leaves and fresh or dry mint leaves were placed in tea bags or cut in 1 cm2 squares, depending on the experiment, and immersed in an aqueous fluid medium. Control samples were heated on a hot plate. MEF treatments were conducted by applying a voltage across electrodes immersed in opposite sides of the beaker. Control and MEF‐treated fresh mint leaf samples heated to 50°C were analyzed by TEM. MEF processing significantly increased the extraction yield for fresh mint leaves because of additional electric field effects during heating. Dried mint leaves and fermented black tea leaves were not affected by the treatment type. Low frequency resulted in higher extraction rates for fresh mint leaves. The electric field strength study showed that electrical breakdown is achieved even at low electric field strengths. MEF treatment shows potential to be used as an alternative to conventional heating for extraction from cellular materials.