Effect Of Moderate Electric Fields Research Articles

Effects of moderate electric fields on the structural and gelling properties of soybean protein isolate gel induced by glucono-δ-lactone

To investigate the effects of moderate electric fields (MEF) treatment on the gelling properties of soybean protein isolate (SPI) gels induced by glucono-δ-lactone (GDL), SPI was treated by applying different electric field intensities (EFI) before GDL-induced gelation. The structure of SPI (4% and 6%, w/v) was characterized via particle size distribution, ζ-potential, fluorescence spectra, and total free sulfhydryl content. The effects of MEF treatment on the acidification pH, rheological properties, water-holding capacity (WHC), textural properties, intermolecular forces, and microstructure of GDL-induced SPI gels were investigated. The results revealed that the SPI gels treated with EFI 4 V/cm aggregated faster during acidification, with higher storage modulus, stronger gel texture, and better deformation resistance. The WHC of the gel was enhanced, and the gel network was finer and more uniform. The results suggested that MEF treatment can improve the characteristics of vegetable protein gels.

Effect of electron-electron interaction on polarization process of exciton and biexciton in conjugated polymers

Abstract By using the one-dimensional tight-binding model modified to include electron-electric field interaction and electron-electron interaction, we theoretically explore the polarization process of exciton and biexciton in cis-polyacetylene. The dynamical simulation is performed by adopting the non-adiabatic evolution approach. The results show that under the effect of moderate electric field, when the strength of electron-electron interaction is weak, the singlet exciton is stable but its polarization presents obvious oscillation. With the enhancement of interaction, it is dissociated into polaron pair, the spin-flip of which could be observed through modulating the interaction strength. For the triplet exciton, the strong electron-electron interaction restrains its normal polarization, but it is still stable. In case of biexciton, the strong electron-electron interaction not only dissociate it, but also flip its charge distribution. We also calculate the yield of the possible states formed after the dissociation of exciton and biexciton.

Effect of Moderate Electric Fields on the Physical and Chemical Characteristics of Cheese Emulsions.

Cheese powder is a multifunctional ingredient that is produced by spray drying a hot cheese emulsion called cheese feed. Feed stability is achieved by manipulating calcium equilibrium using emulsifying salts. However, the increased demand for 'green' products created a need for alternative production methods. Therefore, this study investigated the impact of ohmic heating (OH) on Cheddar cheese, mineral balance, and the resulting cheese feed characteristics compared with a conventional method. A full factorial design was implemented to determine the optimal OH parameters for calcium solubilization. Electric field exposure and temperature had a positive correlation with mineral solubilization, where temperature had the greatest impact. Structural differences in pre-treated cheeses (TC) were analyzed using thermorheological and microscopic techniques. Obtained feeds were analyzed for particle size, stability, and viscosity. OH-treatment caused a weaker cheese structure, indicating the potential removal of calcium phosphate complexes. Lower component retention of OH_TC was attributed to the electroporation effect of OH treatment. Microscopic images revealed structural changes, with OH_TC displaying a more porous structure. Depending on the pre-treatment method, component recovery, viscosity, particle size distribution, and colloidal stability of the obtained feeds showed differences. Our findings show the potential of OH in mineral solubilization; however, further improvements are needed for industrial application.

Effect of moderate electric field on rheological properties, cell wall components, and microstructure of apple tissue

Effect of moderate electric field on rheological properties, cell wall components, and microstructure of apple tissue

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.

Intensifying the moderate electric field-induced modification of maize starch by 1-butyl-3-methylimidazolium chloride

This study aimed to improve the effect of moderate electric field (MEF) treatment on the structural and physicochemical properties of maize starch by adding 1-butyl-3-methylimidazolium chloride ([bmim]Cl). Starch (20%, w/v) was mixed with [bmim]Cl solution (0, 30%, 50%, and 70%, w/w), and then electro-treated (5 V/cm, 50 Hz) at 60 °C for 10 min. As the [bmim]Cl concentration increased, the electro-induced disintegration of starch granules was enhanced due to the intensified Joule heat and decreased pH of reaction bulk. After electro-treated in 70% w/w [bmim]Cl, a transparent solution of starch was observed and the recovered starch tended to dissolve rather than swell in water. Compared with water-bath heating, MEF caused more destruction in the granular and crystal structure, increased the particle size, decreased the pasting viscosity, and reduced the gelatinization enthalpy and thermostability of starch. The obtained results could provide guidance for the application of electro-based techniques in starch modification.

Influence of moderate electric field on sodium caseinate structure and its techno-functionality

This study aimed to evaluate the effect of moderate electric field (MEF) treatment, as a non-thermal technology, on the structure and techno-functionality of sodium caseinate. Colloidal dispersions of caseinate were subjected to different MEF processing conditions (2.56 V cm −1 for 1 and 2 h, 38.46 V cm −1 for 5 and 20 s) and their structural, physical, emulsifying and film-forming characteristics were assessed. The Fourier transform infrared (FTIR) analysis of the caseinate showed higher β-structures and a reduction in random coil conformation after MEF. The MEF-treated dispersions exhibited smaller particle size and developed emulsions with higher physical stability. The process increased the tensile strength (by 6.52–27.37%) and stretchability (by 12.17–54.30%) of caseinate film. A higher glass transition temperature in MEF-processed caseinate films was confirmed by modulated differential scanning calorimetry (MDSC) profiles. The scanning electron microscope (SEM) images showed a more uniform microstructure in treated caseinate films. The results suggest that MEF may be efficiently applied for mild modification of the structure of caseinate resulting in its property improvement. • Moderate electric field (MEF) treatment was applied to sodium caseinate. • MEF presented significant actions on the caseinate structure. • Non-thermal effects of MEF enhanced caseinate techno-functionality. • Treated caseinate yielded emulsions with higher stability and smaller droplet size. • MEF-subjected caseinate films possessed higher mechanical strength and stretchability.

Effect of moderate electric fields on the structural and gelation properties of pea protein isolate

This study aimed to evaluate the effects of moderate electric fields (MEF) inherent in ohmic heating (OH) on the structural and gelling properties of pea protein isolate (PPI). Results showed that OH treatment, especially at high electric field strengths and low frequencies, contributed to the unfolding of protein structures and the formation of smaller aggregates. The OH treatment also increased the surface hydrophobicity (H0) of PPI and reduced the content of free sulfhydryl groups (SH) due to the formation of SS bonds, resulting in the better mechanical properties of PPI gels. The OH-treated gels had the highest water holding capacity and uniform three-dimensional network structure. The OH-treated gels were less hardness, gumminess and chewiness. The OH treatment reduced the storage modulus (G') and loss modulus (G") of the gels. The OH might be an effective technology for fine-tuning legume protein structure and producing protein gels.

Effect of moderate electric field on the quality, microstructure and oil absorption behavior of potato strips during deep-fat frying

Effect of moderate electric field (MEF) on oil distribution and microstructure of fried potato strips was analyzed in this study. MEF with 400 V/m of electric fields strength and 40 KHZ of frequency significantly decreased the matrix oil content from 26.56% to 17.44% ( p = 0.001) and increased the moisture content of potato strips from 51.60% to 54.02% ( p = 0.015) compared with potato strips with intact cell structure, probably due to the electroporation. MEF significantly reduced the L* and b* values and significantly increased P -hardness from 129.76 g to 142.93 g ( p = 0.024). Low-field nuclear magnetic resonance (LF-NMR) found that more oil is distributed on the surface of samples, and scanning electron microscopy (SEM) showed the microstructure of samples was improved with MEF. A similar pattern was observed in potato strips without intact cell structure with MEF. All results suggest the application of MEF in frying industry is helpful. • MEF could significantly reduce the oil absorption of fried potato strips. • The texture and color of fried potato strips was significantly changed by MEF. • The microstructure of fried potato strips was significantly improved by MEF.

Effect of moderate electric field on glucoamylase-catalyzed hydrolysis of corn starch: Roles of electrophoretic and polarization effects

This study aimed to investigate the effect of moderate electric field (MEF, 0–10 V/cm, 50 Hz) on the glucoamylase-catalyzed hydrolysis of corn starch. The underlying mechanism was explored by monitoring changes in the hydrolysis rate, glucoamylase activity, substrate structure, temperature profiles, and hydrolysate properties. The results suggested that the hydrolysis rate highly depended on the MEF intensity. Low-intensity MEF (0–5 V/cm) increased glucoamylase activity by 7.1–22.4% by inducing mild electrophoretic and polarization effects, which resulted in the formation of porous starch. Although high-intensity MEF accelerated the thermal inactivation of glucoamylase, it completely destroyed starch granules due to the extensive ohmic heating; hence, a significant improvement in the hydrolysis efficiency and dramatic decreases in the pasting viscosity, gelatinization enthalpy, and thermo-stability were observed. Overall, this study clarified the mechanism of MEF-assisted enzymatic hydrolysis, which might contribute to expanding the applications of electric field-based techniques in starch modification.

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.

Effects of Moderate Electric Fields on the Post-harvest Preservation of Chestnuts

Ohmic heating (OH) was evaluated as a post-harvest technology to improve chestnuts’ shelf-life (Castanea sativa Mill.) by controlling molds and insect larvae proliferation. Chestnuts were processed by OH at 35, 45, and 55 °C and compared with untreated fruits and the conventional hydrothermal technology (HT - 50 °C for 45 min), which is the process currently used by the chestnut industry. Shelf-life studies were carried out at different atmospheric conditions for 60 days: (i) 25 °C and 40% relative humidity (RH); (ii) 5 °C and 70% RH. The results show that the OH conducted at 55 °C (OH-55 °C), combined with storage at 5 °C, was more effective in controlling molds and larvae growth than the other treatments. Moreover, under these conditions, chestnuts’ shelf-life could be extended for 60 days without substantial changes in the fruits’ color and texture. After the OH-55 °C treatment, lower losses of some nutrients and vitamin C were registered compared to HT. This study demonstrates for the first time that OH has the potential to be used by the chestnut industry for the post-harvest disinfestation of this fruit.

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.

Effects of moderate electric fields on cold-set gelation of whey proteins – From molecular interactions to functional properties

Whey protein gelation and final gel properties are dependent of the gel forming solution characteristics (e.g. protein concentration, pH, ionic strength), and physical variables involved in the method used for gel preparation. Ohmic heating (OH) is an emerging technology in food processing and its application in heat-induced gelation of whey proteins has demonstrated its capacity to influence the physicochemical properties of protein gels. In this work, we studied the OH process and its inherent moderate electric field (MEF) variables - i.e. electric field (EF) strength and frequency - in order to establish their influence in protein aggregation and gelation during WPI cold-set gels formation. The presence of the EF during OH, particularly at higher EF strengths conjugated with lower frequencies, contributed to the formation of smaller aggregates with lower content of reactive thiol groups and lower viscosity. The cold-set gels produced from the aggregates’ suspension presented distinctive properties, influenced by the EF variables. – i.e. higher EF strength and lower frequency. EF treatments give rise to more fine-stranded gels with lower disulphide crosslinking but higher number of hydrophobic interactions and hydrogen bonds. The EF effects during the treatments resulted in weaker, more elastic gels with higher water retention and swelling capacity. These results open novel perspectives for the use of OH as a tool for fine-tuning protein gel networks aiming at enhanced functionality for various applications (e.g. use as texturizer or encapsulating agents).

Effect of moderate electric field on peroxidase activity, phenolic compounds and color during ohmic heating of sugarcane juice

The influence of moderate electric field was evaluated during thermal treatment of sugarcane juice. Conventional and ohmic heating (OH) experiments at temperatures of 60 and 80°C were conducted to investigate the effect of frequency (0–10⁵ Hz), waveform (sine, square, and triangle) and voltage gradient (0–16.7 V/cm) on inactivation of peroxidase (POD), phenolic compounds stability and color changes. Enzyme activity was significantly (p < .05) affected by OH; the nonthermal effects promoted POD activation at 60°C (mainly at 10 Hz) and inactivation at 80°C (mainly at 100 kHz). It was not found variation of phenolic compounds with the different operational conditions applied. Moreover, the color of the juice was modified using low frequency (possibly due to electrochemical reactions) and different waveforms. Overall, OH is suitable for POD inactivation at 80°C with the usual process parameters (sine wave and 60 Hz) or higher frequencies. PRACTICAL APPLICATIONS: Sugarcane juice is a popular energy drink, nonalcoholic, with sweet and pleasant taste. It is commercialized predominantly in the informal marketplace because its processing and marketing are limited due to its rapid deterioration. The objective of this work is to provide an alternative technology for sugarcane juice processing, ensuring safety, and lower impact on nutritional compounds, allowing its commercialization in formal markets. Ohmic heating (OH) is a faster heating technology, appropriate for pasteurization of heat‐sensitive products. The study of the effect of the process variables (temperatures, electric field frequency, waveform, and electric field strength) on enzyme inactivation, degradation of total phenolic compounds, and color stability is important to support modeling and optimization, making OH a viable technology for sugarcane juice pasteurization.

Influence of moderate electric fields in β-lactoglobulin thermal unfolding and interactions

In this study, the effects of moderate electric fields during thermal denaturation of β-lactoglobulin were examined through an in situ circular dichroism approach, complemented by intrinsic extrinsic fluorescence analysis. Results have shown that the effects of electric fields in protein unfolding were linearly dependent on the applied electric field intensity (V/cm) and increased by the use of low electric frequencies – i.e. 50 to 200 Hz. These electric effects caused significant changes on β-lactoglobulin melting temperature, unfolded conformation and subsequent intermolecular interactions, revealed by the increase of surface hydrophobicity (ANS affinity) and higher conservation of retinol binding. The obtained data provides a clear evidence that moderate electric fields contribute to distinct folding/unfolding of β-lactoglobulin, resulting in structural modifications. These findings are relevant for (bio)-technological applications involving electric fields processing, bringing new insights for the development of innovative strategies to control protein function and tune production of functional protein systems.

Electric field effects on β-lactoglobulin thermal unfolding as a function of pH – Impact on protein functionality

Abstract The presence of moderate electric fields (MEF) during ohmic heating (OH) treatment of whey protein systems have demonstrated potential to change physicochemical and functional properties, like aggregation rate and extension or viscoelastic behaviour. However, the specific action of MEF upon the molecular structure of proteins, particularly during thermal processing has yet to be clarified. The effects of MEF in pure fractions of β-lactoglobulin (β-lg) under non-aggregating conditions (low concentration and ionic strength), were investigated in this work. Protein samples were identically heat-treated through conventional and OH methods and at different pH values. β-lg's structural features were characterized by evaluation of secondary structure distribution and local conformational changes using techniques such as circular dichroism, intrinsic and extrinsic fluorescence and free thiol groups reactivity. It was confirmed that MEF affects β-lg upon thermal unfolding, resulting in distinctive structural features, surface hydrophobicity and SH reactivity. The mechanism of action is probably related with the molecular motion induced by the oscillating electric field and is more pronounced at neutral pH, where β-lg is more susceptible to thermal structural changes. These results contribute to a better understanding of OH processing and its effects in food matrices reinforce the possibility of using MEF as a toll to change protein functionality. Industrial relevance Ohmic heating is an emerging technology and is being established as reference method for processing protein-rich food such as dairy and egg products. Non-thermal effects of the applied electric fields during ohmic heating have been addressed but few works deal with their real impact in structural and molecular properties of food proteins with high biological value. In this work demonstrated that the presence of an electric field during ohmic heating processing influences structural aspects of beta-lactoglobulin. This knowledge plays an important role on process design (i.e. pasteurization binomials and fouling control) and product quality because these proteins play an essential role in food's nutritional and organoleptic properties, as well as on functionality, allergenicity and stability aspects.

Effect of moderate electric field on the properties of gelatin capsule residue-based films

This work focused on the development of edible films based on gelatin capsule residue by ohmic heating. The effect of the electric field strength (9.5 V cm−1 and 19 V cm−1) on the mechanical, thermal, physicochemical and morphological properties of films was investigated and compared to films produced by the conventional heating method. Results demonstrated that the application of 9.5 V cm−1 during ohmic heating was able to improve tensile strength from 2.66 MPa to 6.62 MPa in comparison to the conventional method, whereas the film developed using 19 V cm−1 reached a value of 3.26 MPa. Young's Modulus was also significantly increased, while an opposite effect was observed for elongation at break. Modulated differential scanning calorimetry analysis revealed that all samples had two transition temperatures. Electrically treated film (9.5 V cm−1) presented increased crystallinity and thermal stability. Thickness, morphology and water-related properties were not affected by the application of electric field. Films produced by ohmic heating, especially when 9.5 V cm−1 was applied, presented improved mechanical and thermal properties, with increased crystallinity.

Effect of moderate electric fields in the properties of starch and chitosan films reinforced with microcrystalline cellulose

Microcrystalline cellulose (MCC) can provide improved properties when the aim is the development of biodegradable packaging materials. In this work the physicochemical properties of polysaccharide-based films (chitosan and starch) with the incorporation of MCC and the application of moderate electric field (MEF) and ultrasonic bath (UB) as treatments, were evaluated. For each treatment, the thickness, moisture content, solubility, water vapor permeability, contact angle, mechanical properties, along with its color and opacity were determined. The surface morphologies of the films were assessed by scanning electron microscopy (SEM). X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) were also performed. It was observed that the addition of different concentrations of MCC as well as the application of MEF are responsible for changes in the properties of the films, being this effect dependent on the polysaccharide used. Chitosan-based films were slightly yellow, transparent and presented a more homogeneous structure. The use of MEF was efficient in decreasing the permeability to water vapor in chitosan based films without MCC, as well as in production of films with a more hydrophobic surface. The addition of MCC promoted more opaque, rigid, less flexible and less hydrophobic films. Starch-based films were whitish, with a more heterogeneous structure and the application of MEF generated more hydrophilic films with lower tensile strength and Young’s modulus. The films with MCC were more opaque, less flexible and less hydrophilic than the films without MCC. The composites presented good thermal properties, which increases their applicability as packaging materials. Therefore, the incorporation of MCC into polysaccharide-based films as well as the application of MEF can be an approach to change the properties of films.

Development of iron-rich whey protein hydrogels following application of ohmic heating – Effects of moderate electric fields

The influence that ohmic heating technology and its associated moderate electric fields (MEF) have upon production of whey protein isolate cold-set gels mediated by iron addition was investigated. Results have shown that combining heating treatments (90°C, 5min) with different MEF intensities let hydrogels with distinctive micro and macro properties – i.e. particle size distribution, physical stability, rheological behavior and microstructure. Resulting hydrogels were characterized (at nano-scale) by an intensity-weighted mean particle diameter of 145nm, a volume mean of 240nm. Optimal conditions for production of stable whey protein gels were attained when ohmic heating treatment at a MEF of 3V∙cm−1 was combined with a cold gelation step using 33mmol∙L−1 of Fe2+. The consistency index of hydrogels correlated negatively to MEF intensity, but a shear thickening behavior was observed when MEF intensity was increased up to 10V∙cm−1. According to transmission electron microscopy, ohmic heating gave rise to a more homogenous and compact fine-stranded whey protein-iron microstructure. Ohmic heating appears to be a promising technique, suitable to tailor properties of whey protein gels and with potential for development of innovative functional foods.