In-situ activity of α-amylase in the presence of controlled-frequency moderate electric fields

Electrical Fields in the Processing of Protein-Based Foods

Electric field-based technologies offer interesting perspectives which include controlled heat dissipation (via the ohmic heating effect) and the influence of electrical variables (e.g., electroporation). These factors collectively provide an opportunity to modify the functional and technological properties of numerous food proteins, including ones from emergent plant- and microbial-based sources. Currently, numerous scientific studies are underway, contributing to the emerging body of knowledge about the effects on protein properties. In this review, "Electric Field Processing" acknowledges the broader range of technologies that fall under the umbrella of using the direct passage of electrical current in food material, giving particular focus to the ones that are industrially implemented. The structural and biological effects of electric field processing (thermal and non-thermal) on protein fractions from various sources will be addressed. For a more comprehensive contextualization of the significance of these effects, both conventional and alternative protein sources, along with their respective ingredients, will be introduced initially.

Formation of amyloid fibrils from ovalbumin under Ohmic heating

Ohmic heating (OH) is an alternative sustainable heating technology that has demonstrated its potential to modify protein structures and aggregates. Furthermore, certain protein aggregates, namely amyloid fibrils (AF), are associated with an enhanced protein functionality, such as gelation. This study evaluates how Ohmic heating (OH) influences the formation of AF structures from ovalbumin source under two electric field strength levels, 8.5 to 10.5 and 24.0-31.0 V/cm, respectively. Hence, AF aggregate formation was assessed over holding times ranging from 30 to 1200 sunder various environmental conditions (3.45 and 67.95 mM NaCl, 80, 85 and 90 °C, pH = 7). AF were formed under all conditions. SDS-PAGE revealed that OH had a higher tendency to preserve native ovalbumin molecules. Furthermore, Congo Red and Thioflavin T stainings indicated that OH reduces the amount of AF structures. This finding was supported by FTIR measurements, which showed OH samples to contain lower amounts of beta-sheets. Field flow fractioning revealed smaller-sized aggregates or aggregate clusters occurred after OH treatment. In contrast, prolonged holding time or higher treatment temperatures increased ThT fluorescence, beta-sheet structures and aggregate as well as cluster sizes. Ionic strength was found to dominate the effects of electric field strength under different environmental conditions.

Tunning pectinase activity under the effects of electric fields in the enhanced clarification of wine must

Introduction

Pectinolytic enzymes are of great importance for the clarification process of “Vinho Verde” wine must, contributing to the reduction of haze development. During the last decade, a growing body of knowledge has been established about the effects of electric fields on the activation of important food enzymes. However, the influence of electrical parameters on catalytic activity is enzyme-dependent and should be evaluated on a case-by-case basis. This work describes, for the first time, the effects of electric fields and electrical frequency on the activity of pectinase (PEC) in the accelerated clarification of “Vinho Verde” must.

Method

Moderate electric fields (MEF) with intensities below 20 V/cm and at electrical frequencies ranging from 50 to 20 kHz were applied at temperatures between 15 and 35°C. Enzymatic activity was measured for 25 min, and the initial rate of reaction was determined by the coefficient of the linear plot of galacturonic acid (GAL) production as a function of time.

Results

The results show that electrical frequency can increase enzymatic activity depending on temperature conditions; at 20°C and with electrical frequencies of 2 and 20 kHz, enzymatic activity increased by up to 40 and 20%, respectively, when compared with the control sample (without the application of MEF). Temperature dependence was evaluated through the Arrhenius equation, showing that energy of activation (Ea) can be reduced from 9.2 to 6.6 kJ/mol at sub-optimal temperatures for PEC activity when MEF is applied.

Discussion

Electrical parameters, when combined with temperatures below 20°C, reduced pectin concentration in “Vinho Verde” wine must by up to 42% of its initial content. This emergent treatment can be integrated in relevant environmental conditions, presenting an opportunity to increase enzyme efficiency even in low-temperature conditions, which favors the winemaking process.

Effect of pre-gelatinization on α-amylase-catalyzed hydrolysis of corn starch under moderate electric field

This study aimed to explore the roles of starch structure in α-amylase-catalyzed hydrolysis under moderate electric field (MEF). Corn starch was gelatinized by controlling the temperature procedure of rapid viscos-analysis, and then the pre-gelatinized starch (3.0 g) was treated by MEF (2.5 and 5 V/cm) in the presence of α-amylase (1.5 mL). Only a slight hydrolysis occurred for native starch, showing minor increases in reducing sugar content (RSC, ∼0.19 mg/mL), slight changes in granular and semicrystalline structure, and decreases in thermostability (the maximum decomposition temperature (T_max) decreased from 322 to 300 °C). The densely-packed semicrystalline within starch granules was destroyed by pre-gelatinization, thus enhancing the hydrolysis and further decreasing the thermostability, presenting RSC values of 0.63-0.92 mg/mL and T_max of 291-292 °C. Moreover, some special crystals were formed by IEF-induced orientation of hydrolyzed starch chains. Overall, these results confirmed that the semicrystalline structure of starch dominated in MEF-assisted hydrolysis, which could provide guidance for the application of electro-based techniques in starch modification.

Response to "Non-thermal microwave effects: Conceptual and methodological problems"

The objective of this response letter is to expose the reader of Food Chemistry to the most recent advances and discussions about non-thermal effects of microwaves on microorganisms and enzymes. Although these effects showed to be too subtle for any practical use in food processing, experimental and molecular dynamics studies bring evidences that electric fields at low frequencies or with high intensity can have non-thermal effects, such as activity changes in enzymes during ohmic processing or electroporation of cells in pulsed electric field processing. This brief review broadens the scope of this controversial topic to show that innovative experiments and simulations are collaborating with the advance of emerging electro technologies in food processing. .

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.

Electric field effects on proteins - Novel perspectives on food and potential health implications

Electric fields (EF) technologies have been establishing a solid position in emergent food processing and have seen as serious alternatives to traditional thermal processing. During the last decades, research has been devoted to elucidation of technological and safety issues but also fundamental aspects related with interaction of electric fields (EF) with important macromolecules, such as proteins. Proteins are building blocks for the development of functional networks that can encompass health benefits (i.e. nutritional and bioactive properties) but may be also linked with adverse effects such as neurodegenerative diseases (amyloid fibrils) and immunological responses. The biological function of a protein depends on its tridimensional structure/conformation, and latest research evidences that EF can promote disturbances on protein conformation, change their unfolding mechanisms, aggregation and interaction patterns. This review aims at bringing together these recent findings as well as providing novel perspectives about how EF can shape the behavior of proteins towards the development of innovative foods, aiming at consumers' health and wellbeing.

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.

Ohmic heating as a promising technique for extraction of herbal essential oils: Understanding mechanisms, recent findings, and associated challenges

The applicability of ohmic heating, as a volumetric heating technique, has been explored in various sectors of the food industry. The use of ohmic heating for essential oil extraction is among its emerging applications. This chapter overviews the recent progress in this area of research, discusses the mechanisms involved in ohmic-based essential oil extraction processes, explains the effective process parameters, highlights their benefits, and explains the considerations to address the obstacles to industrial implementation. Ohmic-assisted hydrodistillation (OAHD) and ohmic-accelerated steam distillation (OASD) systems were proposed as alternatives to conventional hydrodistillation and steam distillation, respectively. These techniques have successfully extracted essential oils from several aromatic plants (e.g., thyme, peppermint, citronella, and lavender). Both OAHD and OASD possess a number of benefits, such as reducing the extraction time and energy consumption, compared to classical extraction methods. However, these techniques are in their infancy and further economic and upscaling studies are required for their industrial adaptation.