Effects of Pulsed Electric Field (PEF) Treatment on Enhancing Activity and Conformation of α-Amylase

Obtaining bioactive peptides by enhancing enzymatic hydrolysis of salmon by-product proteins through pulsed electric fields (PEF)

Pulsed Electric Fields (PEF) exhibit significant potential to modify proteins and enzymes, enhancing their enzymatic activity and increasing bioactive peptide production. This work aimed to enhance the obtention of bioactive peptides using PEF as a pre-treatment for enzymatic hydrolysis of salmon by-product proteins. Results show that PEF treatments at 15 and 20 kV/cm improved flavourzyme (FV) enzymatic activity by altering the protein's tertiary structure, decreasing its surface hydrophobicity and intrinsic fluorescence. PEF improved the hydrolysis process, especially when both FV and salmon protein were subjected to PEF, increasing the hydrolysis degree and peptide yield from 9.6 % up to 16.6 % and 10.6 % up to 18.7 %, respectively. PEF-assisted hydrolysis modified molecular weight distribution of the peptides obtained, increasing the amount of 3 and 5 kDa peptides. Optimal antioxidant and anti-ACE activities were achieved by applying PEF at FV and SPI at 50 Hz and 15 kV/cm. These findings suggest that PEF is a promising technology for producing bioactive peptides by increasing enzyme activity and improving the obtained peptide yield.

Improvement of lactose digestion by highland barley (Hordeum vulgare var. coeleste L.) β-glucan: Activation of lactase under simulated gastric/small intestinal digestive conditions

β-Galactosidase (lactase) plays a crucial role as a dietary supplement in managing lactose intolerance. Here, the catalytic activity of lactase was successfully activated for the first time through complexation with water-extractable β-glucans from highland barley (WHBG). Under simulated gastric/small intestinal digestive conditions, WHBG and lactase spontaneously formed complexes, resulting in a remarkable increase in catalytic activity up to 172.6 %. Structural analyses revealed that the incorporation of WHBG caused partial unfolding of lactase, thereby exposing its hydrophobic regions with active sites, and the electrostatic and hydrophobic interactions between the two played pivotal roles. Meanwhile, according to microstructure and particle size analyses, the dissociation of aggregates and the re-distribution of lactase molecules were also observed. Consequently, the enzyme-substrate contact was promoted, and the hydrolysis efficiency of complexed lactase in the digestion of lactose in milk was superior to that of native lactase. Notably, among WHBG30/50/70 obtained by continuous fractionation of WHBG with 30 %/50 %/70 % ethanol, WHBG70 exhibited the lowest molecular weights and size, and the highest negative ζ-potential, potentially contributing to its superior activation abilities on lactase. These findings challenge the traditional view of polysaccharides as enzyme inhibitors and highlight their potential for diverse applications.

Assessing the impact of pin-to-plate atmospheric cold plasma on activity, stability, kinetics, and conformation of α-amylase

α-amylase is responsible for shortening the shelf life of food by degrading starch and glycogen into maltose, disaccharides, and oligosaccharides. This study focuses on the effect of atmospheric cold plasma on the activity, stability, enzyme kinetics, and structural change for its application in α-amylase modifications. A reduction in the residual activity from 96.01 % at 170 V to 88.01 % at 230 V after 12 min of treatment was observed in plasma-treated α-amylase compared to the untreated α-amylase at pH 5, 40 °C, after 120 min of reaction time using 2 g 100 mL-1 starch. An increased Km with a reduction in Vmax, kcat, and kcat/Km was observed with increasing voltage and treatment time. An increase in free sulfhydryl content, a decrease in tryptophan fluorescence, an increase in α-helix and β-sheet content, a decrease in β-turn and random coil structures, an increase in surface hydrophobicity, and protein aggregation indicate the structural changes of α-amylase were mainly due to the oxidative effects of reactive plasma species. No change in amide I, II, and III groups suggested plasma treatment did not alter the primary structure of α-amylase. The alteration in secondary, and tertiary structure after plasma treatment resulted in a loss of α-amylase activity.

Efficient and easible biocatalysts: Strategies for enzyme improvement. A review

Owing to the environmental friendliness and vast advantages that enzymes offer in the biotechnology and industry fields, biocatalysts are a prolific investigation field. However, the low catalytic activity, stability, and specific selectivity of the enzyme limit the range of the reaction enzymes involved in. A comprehensive understanding of the protein structure and dynamics in terms of molecular details enables us to tackle these limitations effectively and enhance the catalytic activity by enzyme engineering or modifying the supports and solvents. Along with different strategies including computational, enzyme engineering based on DNA recombination, enzyme immobilization, additives, chemical modification, and physicochemical modification approaches can be promising for the wide spread of industrial enzyme usage. This is attributed to the successful application of biocatalysts in industrial and synthetic processes requires a system that exhibits stability, activity, and reusability in a continuous flow process, thereby reducing the production cost. The main goal of this review is to display relevant approaches for improving enzyme characteristics to overcome their industrial application.

Pulsed Electric Fields Effects on Proteins: Extraction, Structural Modification, and Enhancing Enzymatic Activity

Pulsed electric field (PEF) is an innovative physical method for food processing characterized by low energy consumption and short processing time. This technology represents a sustainable procedure to extend food shelf-life, enhance mass transfer, or modify food structure. The main mechanism of action of PEF for food processing is the increment of the permeability of the cell membranes by electroporation. However, it has also been shown that PEF may modify the technological and functional properties of proteins. Generating a high-intensity electric field necessitates the flow of an electric current that may have side effects such as electrochemical reactions and temperature increments due to the Joule effect that may affect food components such as proteins. This article presents a critical review of the knowledge on the extraction of proteins assisted by PEF and the impact of these treatments on protein composition, structure, and functionality. The required research for understanding what happens to a protein when it is under the action of a high-intensity electric field and to know if the mechanism of action of PEF on proteins is different from thermal or electrochemical effects is underlying.

Distinctive activation of β-galactosidase by carboxymethylated β-glucan in vitro and mechanism study: Critical role of hydrophobic and electrostatic interactions

β-galactosidase (lactase) is commercially important as a dietary supplement to alleviate the symptoms of lactose intolerance. This work investigated a unique activation of CMP (carboxymethylated (1 → 3)-β-d-glucan) on lactase and its mechanism by comparing it with carboxymethyl chitosan (CMCS), an inhibitor of lactase. The results illustrated that the secondary and tertiary structures of lactase were altered and its active sites exposed after complexation with CMP, and dissociation of lactase aggregates was also observed. These changes favored better accessibility of the substrate to the active sites of lactase, resulting in a maximum increase of 60.5 % in lactase activity. Furthermore, the hydrophobic and electrostatic interactions with lactase caused by the carboxymethyl group of CMP were shown to be crucial for its activation ability. Thus, the improvement of lactase activity and stability by CMP shown here is important for the development of new products in the food and pharmaceutical industries.

Impact of non-thermal techniques on enzyme modifications for their applications in food

The present review elaborates on the details of the enzyme, its structure, specificity, and the mechanism of action of selected enzymes as well as structural changes and loss or gain of activity after non-thermal treatments for food-based applications. Enzymes are biological catalysts found in various systems such as plants, animals, and microorganisms. Most of the enzymes have their optimum pH, temperature, and substrate or group of substrates. The conformational modification of enzymes either increases or decreases the rate of reaction at different pH, and temperature conditions. Enzymes are modified by different techniques to enhance the activity of enzymes for their commercial applications mainly due to the high cost of enzymes, stability, and difficulties that occur during the use of enzymes in different conditions. On the opposite, enzyme inactivation provides its application to extend the shelf life of fruits and vegetables by denaturation and partial inactivation of enzymes. Hence, the activation and inactivation of enzymes are studied by non-thermal techniques in both the model and the food system. The highly reactive species generated during non-thermal techniques cause chemical and structural modification. The enzyme modifications depend on the type and source of the enzyme, type of technique, and the parameters used.

Structure-based modification of a-amylase by conventional and emerging technologies: Comparative study on the secondary structure, activity, thermal stability and amylolysis efficiency

α-Amylase is an endo-enzyme that catalyzes the hydrolysis of starch into shorter oligosaccharides. α-Amylase plays a crucial role in various industries. Manipulated α-amylases are of particular interest due to their remarkable amylolysis efficiency and thermostability for large-scale biotechnological processes. The retained catalytic activity of enzymes is decreased according to extreme pH, temperature, pressure, and chemical reagents. Broad industrial applications of α-amylases need special properties such as stability against temperature, pH, and chelators, and also attain reusability, desirable enzymatic activity, efficiency, and selectivity. Considering the biotechnological importance of α-amylase, its high stability is the most critical challenge for its economic viability. Therefore, improving its functionality and stability recently gained much interest. To achieve this purpose, various emerging technologies in combination with conventional methods on α-Amylases with different sources have been conducted. The present review is an attempt to summarize the effect of various conventional methods and emerging technologies employed to date on α-amylase secondary structure, thermal stability, and performance.

Influence of Supercritical Carbon Dioxide on the Activity and Conformational Changes of α-Amylase, Lipase, and Peroxidase in the Solid State Using White Wheat Flour as an Example

Green technologies using renewable and alternative sources, including supercritical carbon dioxide (sc-CO2), are becoming a priority for researchers in a variety of fields, including the control of enzyme activity which, among other applications, is extremely important in the food industry. Namely, extending shelf life of e.g., flour could be reached by tuning the present enzymes activity. In this study, the effect of different sc-CO2 conditions such as temperature (35-50 °C), pressure (200 bar and 300 bar), and exposure time (1-6 h) on the inactivation and structural changes of α-amylase, lipase, and horseradish peroxidase (POD) from white wheat flour and native enzymes was investigated. The total protein (TPC) content and residual activities of the enzymes were determined by standard spectrophotometric methods, while the changes in the secondary structures of the enzymes were determined by circular dichroism spectrometry (CD). The present work is therefore concerned for the first time with the study of the stability and structural changes of the enzyme molecules dominant in white wheat flour under sc-CO2 conditions at different pressures and temperatures. In addition, the changes in aggregation or dissociation of the enzyme molecules were investigated based on the changes in particle size distribution and ζ-potential. The results of the activity assays showed a decrease in the activity of native POD and lipase under optimal exposure conditions (6 h and 50 °C; and 1 h and 50 °C) by 22% and 16%, respectively. In contrast, no significant changes were observed in α-amylase activity. Consequently, analysis of the CD spectra of POD and lipase confirmed a significant effect on secondary structure damage (changes in α-helix, β-sheet, and β-turn content), whereas the secondary structure of α-amylase retained its original configuration. Moreover, the changes in particle size distribution and ζ-potential showed a significant effect of sc-CO2 treatment on the aggregation and dissociation of the selected enzymes. The results of this study confirm that sc-CO2 technology can be effectively used as an environmentally friendly technology to control the activity of major flour enzymes by altering their structures.

Investigation into the chemical modification of α-amylase using octenyl succinic anhydride: enzyme characterisation and stability studies

The present study describes the chemical modification of α-amylase using succinic anhydride (SA), phthalic anhydride (PA) and a novel modifier viz. 2-octenyl succinic anhydride (2-OSA). SA-, PA- and 2-OSA-α-amylases displayed a 50%, 91% and 46% increase in stability at pH 9, respectively; as compared to unmodified α-amylase. PA-α-amylase showed a significant increase in Ea and ΔH_a^#, and a concomitant decrease in ΔS_a^#. The modified α-amylases exhibited improved thermostability as reflected by significant reductions in K_d and ΔS_d^#, and increments in t_1/2, D-, E_d, ΔH_d^# and ΔG_d^# values. The modified α-amylases displayed variable stabilities in the presence of different surfactants, inhibitors, metal ions and organic solvents. Interestingly, the chemical modification was found to confer resistance against inactivation by Hg²⁺ on α-amylase. The conformational changes in modified α-amylases were investigated using intrinsic tryptophan fluorescence, ANS (extrinsic) tryptophan fluorescence, and dynamic fluorescence quenching. Both intrinsic and extrinsic tryptophan fluorescence spectra showed increased fluorescence intensity for the modified α-amylases. Chemical modification was found to induce a certain degree of structural rigidity to α-amylase, as shown by dynamic fluorescence quenching. Analysis of the CD spectra by the K2d method using the DichroWeb online tool indicated evident changes in the α-helix, β-sheet and random coil fractions of the α-amylase secondary structure, following chemical modification using anhydrides. PA-α-amylase exhibited the highest productivity in terms of hydrolysis of starch at 60 °C over a period of 5 h indicating potential in varied biotechnological applications.

Effect of pulsed electric field on soybean isoflavone glycosides hydrolysis by β-glucosidase: Investigation on enzyme characteristics and assisted reaction

This work aimed to investigate how pulsed electric field (PEF) technology as an alternative to enhance the enzymatic hydrolysis of soybean isoflavone glycosides (SIG). To achieve it, the effect of PEF treatment on the activity, kinetics, thermodynamics and structure of β-glucosidase (β-GLU) were evaluated. The parameters for PEF-assisted hydrolysis of soybean isoflavone glycosides were optimized by response surface methodology. The results showed that PEF treatment increased the relative activity and catalytic efficiency of β-GLU with moderate electric field intensity. Furthermore, PEF treatment induced the secondary and tertiary structural change of β-GLU, the α-helix content increased by 4.23% and the β-fold content decreased by 3.70%. The optimum conditions for PEF treatment were established as the highest yield of isoflavone aglycones achieved 94.58%. Therefore, these results indicated that PEF treatment could be used as an efficient process to improve the β-GLU properties, converting soybean isoflavone glycoside to their aglycones form.

Application of magnetic field (MF) as an effective method to improve the activity of immobilized Candida antarctica lipase B (CALB)

The process of immobilized enzyme and the change mechanism of enzyme in magnetic field.

Molecular dynamics evidence for nonthermal effects of electric fields on pectin methylesterase activity

Experimental studies relevant to the nonthermal effects of electric fields on biological systems are emerging. However, these effects are poorly understood at the molecular level. The present study investigates pectin methylesterase, a cell wall modifying enzyme in plants, exposed to various electric field strengths. Molecular dynamics (MD) of the enzyme were studied with and without (thermal-only) electric field applications. The measurements were interpreted on the basis of equivalent energy input to gain insights into the effect of electric field treatment time at a constant temperature (50 °C). Results reveal that electric fields exert nonthermal effects on both local and global protein structure. In 1 μs simulations, the results show significant (P ≤ 0.05) shrinkage of the catalytic domain and shortening of enzyme-water hydrogen bond lifetime by a 50 V cm-1 electric field. Unwinding of the helical segments, altered intra- and intermolecular hydrogen bond patterns, and increased hydration are also caused by the 50 V cm-1 electric field. This study serves to understand the electric field influence on the functional role of proteins.

Electro-opening of a microtubule lattice in silico

Modulation of the structure and function of biomaterials is essential for advancing bio-nanotechnology and biomedicine. Microtubules (MTs) are self-assembled protein polymers that are essential for fundamental cellular processes and key model compounds for the design of active bio-nanomaterials. In this in silico study, a 0.5 μs-long all-atom molecular dynamics simulation of a complete MT with approximately 1.2 million atoms in the system indicated that a nanosecond-scale intense electric field can induce the longitudinal opening of the cylindrical shell of the MT lattice, modifying the structure of the MT. This effect is field-strength- and temperature-dependent and occurs on the cathode side. A model was formulated to explain the opening on the cathode side, which resulted from an electric-field-induced imbalance between electric torque on tubulin dipoles and cohesive forces between tubulin heterodimers. Our results open new avenues for electromagnetic modulation of biological and artificial materials through action on noncovalent molecular interactions.

Effect of metal salts on α-amylase-catalyzed hydrolysis of broken rice under a moderate electric field

This study aimed to evaluate the effects of metal salts on α-amylase-catalyzed hydrolysis of broken rice under a moderate electric field (MEF) by monitoring changes in hydrolysis efficiency, temperature, α-amylase activity, starch-metal ion interaction, and the structural and physicochemical properties of hydrolysates. Results showed that metal salts affected the hydrolysis mainly by altering α-amylase activity rather than by inducing thermal effect or interacting with starch. Reducing sugar content reached 125.0 g/L, while α-amylase activity increased by 18.16% when treated with 0.12 mmol/L Ca²⁺. Holes on hydrolysates treated with Ca²⁺ and Mg²⁺ were larger than those treated with Mn²⁺ and Cu²⁺. No M-O bond was formed after the hydrolysis. The crystallinity was slightly increased with the hydrolysis and the values for Ca²⁺- and Mg²⁺-treated samples were larger. The water and oil absorption capacity of the hydrolysate treated with Ca²⁺ was the highest. This study extended the knowledge of the roles of metal ions on MEF-assisted enzymatic hydrolysis and will contribute to the development of an innovative technology for starch modification.

Ultrasound enhanced the binding ability of chitinase onto chitin: From an AFM insight

In order to evaluate the effect of ultrasound to chitinase from a molecular level, atomic force microscopy (AFM) was employed to investigate the interaction force of chitinase binding onto chitin surface. In the measurement of force-distance curve, a series of pull-off events were discovered using the immobilized AFM tips with chitinase either treated by ultrasound or not, whereas no interaction peak was observed by the AFM tips without chitinase, indicating that the obtained adhesion forces were coming from the binding functions between chitinase and chitin. Through the analysis of these force curves, at the loading velocity of 0.3 μm/s, the maximum binding force of the chitinase treated by ultrasound for 20 min onto chitin was measured to be 105.33 ± 23.51 pN, while the untreated onto chitin was 71.05 ± 12.73 pN, suggesting the stronger binding force between ultrasonic treated chitinase and chitin substrate. Therefore, AFM has provided a useful method to directly and quantitatively characterize the interactions between chitinase and chitin, and successfully proved that ultrasound could activate chitinase by enhancing the binding ability of chitinase onto chitin.

Review of the application of pulsed electric fields (PEF) technology for food processing in China

With the improvement of living standards, growing consumer demand for high-quality and natural foods has led to the development of new mild processes to enhance or replace conventional thermal and chemical methods for food processing. Pulsed electric fields (PEF) is an emerging and promising non-thermal food processing technology, which is ongoing from laboratory and pilot plant level to the industrial level. Chinese researchers have made tremendous advances in the potential applications of PEF for processing a wide range of food commodities over the last few years, which contributes to the current understanding and development of PEF technology. The objective of this paper is to conduct a systematic review on the achievements of PEF technology used for food processing in China and the corresponding processing principles. Research on the applicability of PEF in food processing suggests that PEF can be used alone or in combination with other methods, not only to inactivate microorganisms and extract active constituents, but also to modify biomacromolecules, enhance chemical reactions and accelerate the aging of fermented foods, which are mainly related to permeabilization of biomembranes, occurrence of electrochemical and electrolytic reactions, polarization and realignment of molecules, and reduction of activation energy of chemical reactions induced by PEF treatments. In addition, some of the most important challenges for the successful implementation of large-scale industrial applications of PEF technology in the food industry are discussed. The results bring out the benefits of both researchers and the industry.

Electro-chemo-mechanical model to investigate multi-pulse electric-field-driven integrin clustering

The effect of pulsed electric fields (PEFs) on transmembrane proteins is not fully understood; how do chemo-mechanical cues in the microenvironment mediate the electric field sensing by these proteins? To answer this key gap in knowledge, we have developed a kinetic Monte Carlo statistical model of the integrin proteins that integrates three components of the morphogenetic field (i.e., chemical, mechanical, and electrical cues). Specifically, the model incorporates the mechanical stiffness of the cell membrane, the ligand density of the extracellular environment, the glycocalyx stiffness, thermal Brownian motion, and electric field induced diffusion. The effects of both steady-state electric fields and transient PEF pulse trains on integrin clustering are studied. Our results reveal that electric-field-driven integrin clustering is mediated by membrane stiffness and ligand density. In addition, we explore the effects of PEF pulse-train parameters (amplitude, polarity, and pulse-width) on integrin clustering. In summary, we demonstrate a computational methodology to incorporate experimental data and simulate integrin clustering when exposed to PEFs for time-scales comparable to experiments (seconds-minutes). Thus, we propose a blueprint for understanding PEF/electric field effects on protein induced signaling and highlight key impediments to incorporating experimental values into computational models such as the kinetic Monte Carlo method.

Impacts of short-term germination on the chemical compositions, technological characteristics and nutritional quality of yellow pea and faba bean flours

In the present study, yellow pea (CDC Amarillo) and faba bean (CDC Snowdrop) seeds were soaked overnight and then germinated in the dark at ambient temperature for 24, 48 and 72 h. During the short-term germination, germination percentages higher than 96.6% were achieved and progressive growth of radicles was observed for both varieties. The soaked and germinated seeds were dried at 55 °C and milled into flours, and their chemical compositions, physicochemical properties and in vitro starch and protein digestibility were systematically examined. Overall, soaking and germination did not noticeably alter the chemical compositions of each flour. The most obvious changes in the physicochemical properties were found in the pasting, emulsifying and foaming properties of the pulse flours. Soaking and 24-h germination greatly enhanced the pasting viscosities of the flours; as the germination proceeded, their viscosities gradually decreased, resulting from the degradation of starch by endogenous amylase(s) during pasting. Germination progressively improved the emulsion activity and stability, foaming capacity and foam stability of both pulse flours. In addition, germination enhanced the in vitro digestibility of starch and protein of the flours; however, the treatment did not improve their in vitro protein digestibility corrected amino acid scores (IV-PDCAAS). Short-term germination of 24-72 h has been demonstrated to be an effective approach to generating pulse flours possessing diverse functional properties and enhanced digestibility of macronutrients.

Ultrasound promotes enzymatic reactions by acting on different targets: Enzymes, substrates and enzymatic reaction systems

With the extensive application of enzyme-catalyzed reactions in numerous fields, improving enzymatic efficiency has attracted wide attention for reducing operating costs and increasing output. There are three targets throughout enzymatic reactions: the enzyme, substrate, and mixed reaction system. Ultrasound has been known to accelerate enzymatic reactions by acting on different targets. It can modify both enzyme and substrate macromolecules, which is helpful for enhancing enzyme activity and product yields. The synergistic effect of ultrasound and enzymes is widely reported to increase catalytic rates. The present review discusses the positive effect induced by ultrasound throughout the enzymatic process, including ultrasonic modification of enzymes, ultrasound assisted immobilization, ultrasonic pretreatment of substrates, and ultrasound assisted enzymatic reactions.