Effect of electric field on physicochemical properties and resistant starch formation in ohmic heating processed corn starch

This research investigated the impact of ohmic heating (OH) on the physicochemical properties and resistant starch formation in native corn starch. Electric field strengths (EFS) of 50, 75, and 100 V/cm were applied to native starch, at a starch-water ratio of 1:1 w/v. The conductivity of the medium is a crucial factor in ohmic heating. In this study, the conductivity values at 120 °C were measured at 1.5 mS/m. The study revealed two distinct outcomes resulting from the application of different EFS. Firstly, a thermal effect induced gelatinization, resulting in a reduction in the enthalpy of corn starch, an increase in the water absorption index (WAI) and the water solubility index (WSI), and a decrease in peak viscosity. Secondly, a non-thermal effect of OH was observed, leading to the electrolysis of certain starch compounds and water. This electrolysis process generated radicals (-OH) that interacted with starch components, augmenting the percentage of resistant starch. This increase was associated with elevated levels of carbonyl and carboxyl groups at 75 and 100 V/cm.

Impact of thermal and nonthermal process intensification techniques on yield and quality of virgin coconut oil

Virgin coconut oil (VCO) is valued for its nutraceutical potential. The focus of this research was to assess the effect of selected thermal and nonthermal pre-treatments on the yield and quality of subsequently wet-extracted VCO. The fresh coconut cream was subjected to microwave heating (450 W, 2 min), ohmic heating (180 V, 5 min), ultrasonication (350 W, 10 min), or a pulsed electric field (40 kV cm-1, 12.32 min). The thick cream was separated, and VCO was obtained after a freeze-thaw process. The highest VCO yields (>93%) were observed in the cases of ultrasonicated and pulsed electric field-treated samples. A range of oil quality parameters, total phenolic content, and antioxidants were evaluated. Further, the fatty acid composition of all oils was studied. Observations from this research indicate that ultrasonication pre-treatment resulted in the best VCO yield and quality.

Electrothermal interfacial evaporation through carbon-nanostructured composite membranes

High energy demand required in membrane distillation (MD) process to heat feed water and maintain the necessary temperature gradient across the membrane presents a challenge to widespread adoption of MD. In response to this challenge, surface heating membrane distillation (SHMD) has emerged as a promising solution. SHMD can employ solar or electrical energy to directly heat the membrane and feed, eliminating the need for an external heat source to heat feed water. In this study, we explore electrothermally-driven interfacial evaporation using a multi-walled carbon nanotube (MWCNT)-based composite membrane and further envision its utilization for high-efficient SHMD. Upon application of voltage, the resistance of the MWCNT leads to the conversion of electrical energy into heat, which is then uniformly transferred to feeds. The MWCNT-based composite membrane exhibited an evaporative water flux of up to 2.34 kg m-2h-1 with an associated energy efficiency of 61% and demonstrated outstanding localized surface heating performance. The employed membranes exhibited no significant variations in either resistance or surface temperature, regardless of the direction of the applied electric field. Energy parameters from the electrothermal membranes showed quantitative agreement with values reported for various electrothermal MD systems, suggesting the potential of the composite membranes in energy-efficient and cost-effective localized heating MD applications.

Effects of ohmic heating with different voltages on the quality and microbial diversity of cow milk during thermal treatment and subsequent cold storage

Ohmic heating (OH), an innovative heating technology, presents potential applications in the pasteurization of liquid foods. Therefore, the study was conducted to evaluate the effect of OH at various voltage gradients (10 V/cm, 12.5 V/cm, and 15 V/cm) and water bath (WB) on microbial inactivation, physicochemical and sensory properties and microbial flora of pasteurized milk. Results indicated that OH with higher voltage could effectively inactivate microorganisms in milk, requiring less heating time and energy. Moreover, OH treatment at higher voltages could decelerate lipid oxidation and better maintain the sensory quality and essential amino acids content of milk. Additionally, all treatments significantly altered the microbial community, and during storage, the microbial community in milk treated with 10 V/cm and 12.5 V/cm OH remained relatively stable. OH treatments with voltage gradients exceeding 12.5 V/cm could effectively inactive microorganisms and maintain the quality attributes of milk.

Innovative date syrup processing with ohmic heating technology: Physiochemical characteristics, yield optimization, and sensory attributes

The present study aimed to investigate the application of the ohmic heating (OH) technique in the production of date syrup from the date fruit of the Sukkary variety at different electric field strengths (EFS) (9, 10, and 11 V/cm). The results were compared to the conventional heating method (CH). The response surface methodology was used to optimize yield. The results showed that the time to reach the boiling point of dates and water mixture using OH was less than the CH by 80% for extracting and 900% for evaporation. In addition, the productivity of date syrup using OH at EFS of 11 V/cm was higher than the CH by 86.11%. There is no significant effect between OH at EFS of 11 V/cm and CH in moisture content, refractive index, density, TSS, and viscosity. The optimum level of EFS was 11.5 V/cm, which gave a higher yield (64.93%). OH, save consumed power and cost. The OH gave the highest scores of sensory characteristics compared to CH. Total sugars, monosaccharides, and ketone monosaccharides were detected in the date syrup, and the result was positive, while the quintuple sugars and multiple sugars were negative for all treatments. The OH reduced the cost by 85.78% compared with CH.

Application of novel pretreatment technologies for intensification of drying performance and quality attributes of food commodities: a review

Drying is an energy-intensive process that can be reduced by the application of pretreatment prior to drying to enhance mass transfer and minimize energy consumption. This review summarizes the mechanistic aspects and applications of emerging pretreatment approaches, namely ohmic heating (OH), ultrasound (US), high pressure processing (HPP), and pulsed electric field (PEF), with emphasis on the enhancement of mass transfer and quality attributes of foods. Novel pretreatments significantly improved the drying efficiency by increasing mass transfer, cavitation, and microchannel formation within the cell structure. Various processing parameters have great influence on the drying performance and quality attributes of foods. Several studies have shown that novel pretreatments (individual and combined) can significantly save energy while improving the overall drying performance and retaining the quality attributes. This work would be useful for understanding the mechanisms of novel pretreatment technologies and their applications for future commercial research and development activities.

Combination of ohmic heating and subcritical water to recover amino acids from poultry slaughterhouse waste at a pilot-scale: new valorization technique

Considering the global need for waste valorization and enhancing resource efficiency, this study investigated the possibility of recovering amino acids from underutilized chicken heads and legs as poultry by-products. In this sense, a new combined technique was developed based on ohmic heating (OH) and subcritical water (SCW), i.e., OHSCW. Besides, the effects of OH at different electric field strengths (5.71, 7.14, and 8.57 V/cm) and times (15, 30, and 45 min) were compared with the control treatment (SCW equipped with conventional heating, without OH) at a temperature of 140 °C. The results showed that the come-up time using OHSCW, at electric field strengths of 7.14 and 8.57 V/cm, was less than the control method by 17 and 75%, respectively. The lowest specific energy consumption was 403.68 kJ/kg which was 59.22% less than the control method. The highest energy efficiency was 93.88% at the electric field strength of 8.57 V/cm which was superior to that of the control treatment, i.e., 47.13%. The amounts of total amino acids recovered by OHSCW, at an electric field strength of 8.57 V/cm, were higher than the control method by 70.48%. OHSCW at an electric field strength of 5.71 V/cm yielded the maximum recovery efficiency of amino acids (79.40%) while recovery efficiency in control treatment was 15.48%. Besides, the results of Amino acid Analyzer (AAA) showed that the recovered amino acids include asparagine, serine, glutamine, glycine, threonine, histidine, cysteine, alanine, aspartic, tryptophan, arginine, tyrosine, valine, methionine, isoleucine, leucine, and phenylalanine.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05556-4.

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. .

Optimization of process conditions for effective ohmic heating of greater lizardfish () sausage via response surface methodology

In current research, the optimization of ohmic heating on greater lizardfish (Saurida tumbil) sausage variables was carried out using response surface methodology-central composite design (RSM-CCD). The effect of process variables including voltage gradient (15-60 V/cm), time (1-15 min), and temperature (60-90^°C) on the microbial properties, pH, peroxide value, water holding capacity (WHC), and cooking loss of the sausages was evaluated. The results showed that the characteristics of the sausages were dependent on the ohmic heating conditions and these properties can be modulated. As per the results, the voltage gradient and temperature has a significant effect on the total plate count (p < 0.05). The increase in voltage gradient was the most effective on pH (5.63-6.91). The interaction terms of all items had a significant effect (p < 0.05) on the peroxide value of the fish sausages. Higher amount of temperature and process time were resulted in the more cooking loss. Increasing the voltage gradient was more effective on WHC compared to the temperature. Finally, the process was optimized and the optimized condition was achieved by setting the voltage gradient at 30 V/cm, process time at 4 min, and temperature at 66°C. Also, it was compared with conventional heating. The results were shown that the differences between the mean values of all responses were statistically significant (p < 0.05) except for pH. Therefore, ohmic method was carried out faster, with lower temperature and obtaining the highest WHC and lowest total plate count, peroxide value, cooking loss, and optimized pH. Generally, this study suggested that the ohmic heating can be used as a rapid and homogeneous cooking method for the preparation of sausages from greater lizardfish as a commercial low-valued fish.

Continuous pressurized extraction versus electric fields-assisted extraction of cyanobacterial pigments

Cyanobacteria pigments, in special carotenoids and phycobiliproteins, are usually used in industry as raw extracts, although there is still no standard methodology for their extraction. For the co-extraction of carotenoids and phycobiliproteins from the marine cyanobacterium Cyanobium sp., a continuous pressurized solvent extraction (CPSE) system and an electric fields-assisted extraction system based in ohmic heating were optimized using Central Composite Designs, with three factors each: time (t), temperature (T) and, flow (f) for CPSE; and time, temperature and frequency (F) for ohmic heating. The content of pigments and the antioxidant capacity of extracts were evaluated. All tested factors seem to influence the extraction of pigments in different ways: a high temperature (70 °C) had a positive impact on the extraction rate in both methods, while the influence of time depended on the extraction principle. Flow and frequency affected directly the extraction efficiency and these methods are indeed suitable for cyanobacterial pigments extraction, achieving good extraction results. Optimal conditions for co-extraction of carotenoids and phycobiliproteins in CPSE were T = 70 °C, t = 20 min and f = 1.5 mL min^-1, and for ohmic heating they were T = 70 °C, t = 5 min and F = 20 kHz. Both, CPSE and ohmic heating systems allowed obtaining better extraction yields when compared with a previously optimized extraction method (homogenization), used here as a reference. However, ohmic heating was the best methodology for pigments co-extraction from Cyanobium sp.

Novel inactivation methods of Doenjang (fermented soybean paste) by high pressure and ohmic heating

The changes of the total cell number in doenjang (Korean traditional fermented soybean paste) by conventional conduction heating, high pressure non-thermal treatment, and ohmic heating were compared. A total of (10¹-10²) CFU/g cells were decreased by heating at (100-105) °C for 10 min. The inactivation rate was improved when heated to a temperature higher than 110 °C, but the taste, color of doenjang were severely changed. Inactivation by high pressure at (200-800) MPa was not achieved, because the total cell did not reach a reduction of 10¹ CFU/g. The total bacterial counts of 10³ CFU/g were decreased during ohmic heating at 15 V and 60 Hz for 10 min, and showed the most effective inactivation. Therefore, application of the ohmic heating in doenjang with high viscosity can kill target microorganisms related to quality deterioration, and rapid and uniform ohmic heating leads to reduction in sensory quality damage.

Comparative transcriptomic study of Escherichia coli O157:H7 in response to ohmic heating and conventional heating

In this study, the high-throughput Illumina HiSeq 2000 mRNA sequencing technique was used to investigate the transcriptome response of Escherichia coli O157:H7 exposed to ohmic heating (OH) and water bath heating (WB). Compared to untreated samples, a total of 293, 516, and 498 genes showed differential expression after HVOH (high voltage short time ohmic heating), LVOH (low voltage long time ohmic heating), and WB, respectively. Therefore, LVOH had the potential to cause comparable effects on the transcriptome of E. coli O157:H7 as compared to WB, but not HVOH. These results indicated that additional non-thermal effects were not reflected on transcriptome of E. coli O157:H7 using both HVOH and LVOH, in particular the HVOH. Most of differentially expressed genes involved in information storage and processing, and cellular processes and signaling showed up-regulation whereas most of genes related to the metabolism were down-regulated after HVOH, LVOH, and WB. In addition, more attention needs to be paid to the up-regulation of a large number of virulence genes, which might increase the ability of surviving E. coli O157:H7 to infect host cells after HVOH, LVOH, and WB. This transcriptomic study on the response of E. coli O157:H7 to OH protomes the understanding of inactivation mechanism of OH on the molecular level and opens the door to future studies for OH.

Production of grape pekmez by Ohmic heating-assisted vacuum evaporation

Pekmez is a concentrated syrup-like food conventionally produced by vacuum evaporation process from sugar-rich fruits. In this study, the applicability of grape pekmez production by ohmic heating assisted vacuum evaporation (ΩVE) method was investigated. Conventional vacuum evaporation (CVE) and ΩVE methods were compared in terms of physicochemical properties, HMF (5-hydroxymethylfurfural) contents, rheological properties, and energy consumptions. ΩVE was run at four different voltage gradients (17.5, 20, 22.5, and 25 V/cm). Total process times for grape pekmez production were determined as 57, 28.5, 32, 39, and 50 minutes for CVE, ΩVE (25 V/cm), ΩVE (22.5 V/cm), ΩVE (20 V/cm) and ΩVE (17.5 V/cm), respectively. Energy consumption of CVE method was higher than ΩVE method for all voltage gradients. Energy efficiency increased as the voltage gradient increased. There was no significant difference between CVE and ΩVE methods for HMF contents. The results show that the ΩVE method could be an alternative to the CVE process for grape pekmez production.

and the formation of bioactive compounds in infant formula

The effect of ohmic heating (OH) (50, 55, and 60 °C, 6 V/cm) on the inactivation kinetics (Weibull model) and morphological changes (scanning electron microscopy and flow cytometry) of Salmonella spp. in infant formula (IF) was evaluated. In addition, thermal load indicators (hydroxymethylfurfural and whey protein nitrogen index, HMF, and WPNI) and bioactive compounds (DPPH, total phenolics, ACE, α-amylase, and α-glucosidase inhibitory activities) were also studied. OH presented a more intense inactivation rate than conventional heating, resulting in a reduction of about 5 log CFU per mL at 60 °C in only 2.91 min, being also noted a greater cell membrane deformation, higher formation of bioactive compounds, and lower values for the thermal load parameters. Overall, OH contributed to retaining the nutritional value and improve food safety in IF processing.

Hygienization of mixed animal by-product using pulsed electric field in a continuous treatment system: Synergistic effect with ohmic heating on the inactivation of indicator bacteria

Thermal hygienization of waste animal by-products (ABP) before anaerobic digestion is imposed by EU regulations in order to minimize its sanitary risk during digestate land application. This process is energy and time consuming. The present paper deals with the hygienization of ABP using pulsed electric field (PEF) in a continuous system. Enterococcus faecalis ATCC 19433 and Escherichia coli ATCC 25922 were tested as indicator bacteria characterizing the microbial inactivation efficiency. Four electric field strengths (15, 20, 25 and 30 kV∙cm^-1) were applied to the continuous treatment chamber where circulated the ABP suspension. Synergistic effect of PEF and ohmic heating (T_ave = 41 °C) and single effect of PEF (T_ave = 28 °C) on bacterial inactivation were investigated. With the effect of ohmic heating, PEF treatment at 25 and 30 kV∙cm^-1 for 0.9 ms could obtain 5-log10 reduction of Ent. faecalis. This efficiency complies with the EU criteria to validate an alternative hygienization process. The time estimated by Weibull model for 5-log10 reduction of both indicator bacteria (5-D value) was significantly reduced by 2-24.5 times when the synergistic effect of PEF and ohmic heating was present. The increase in electric field strength from 25 kV∙cm^-1 to 30 kV∙cm^-1 did not amount to a further inactivation. PEF process coupling ohmic heating at 25 kV∙cm^-1 was the most efficient for ABP hygienization among the four electric field strengths studied.

Pilot-scale ohmic heating-assisted extraction of wheat bran bioactive compounds: Effects of the extract on corn oil stability

Recent studies introduced ohmic heating-assisted extraction (OHAE) as a promising emerging technology at laboratory-scales. The objectives of the present study were, first, to investigate the applicability of OHAE at pilot-scale for extraction of bioactive compounds from wheat bran immersed in a polar solvent (salted water containing 0.1% NaCl) at the electric field strengths (EFS) of 4.28, 7.90, and 15.71 V/cm and, second, to evaluate the effects of the wheat extracts on the corn oil stability during 30 days of storage at 45 °C. The results showed that OHAE saved 63% of energy consumption compared with the conventional extraction method. Also, the scaled-up OHAE unit yielded extracts with high quantities of bioactive compounds (110-460 ppm total phenolics) and higher antioxidant activities (antioxidant effectiveness of 56-84%) than those of the extract obtained through the conventional extraction method, i.e., 95 ppm total phenolics with antioxidant effectiveness of 51%. Increasing the EFS increased total phenolics and antioxidant effectiveness of extracts. The incorporation of 250 ppm of the extract obtained at the highest EFS effectively postponed the oxidation of corn oil during one month of storage (peroxide value of 7 vs. 19 meq/kg compared with the control sample) and extended the half-life of oil from 11 to 26 days. Besides, mathematical models proposed in this study well-predicted the oxidation stability of the oil samples mixed with the extract.

A study on the energy and exergy of Ohmic heating (OH) process of sour orange juice using an artificial neural network (ANN) and response surface methodology (RSM)

The nonmodern statistical methods are often unusable for modeling complex and nonlinear calculations. Therefore, the present research modeled and investigated the energy and exergy of the ohmic heating process using an artificial neural network and response surface method (RSM). The radial basis function (RBF) and the multi-layer perceptron (MLP) networks were used for modeling using sigmoid, linear, and hyperbolic tangent activation functions. The input consisted of voltage gradient; weight loss percentage, duration ohmic, Input flow, Power consumption, electrical conductivity and system performance coefficient and the output included the energy efficiency, exergy efficiency, exergy loss, and improvement potential. The response surface method was also used to predict the data. According to the result, the best prediction amount for energy and exergy efficiencies, exergy loss and improvement potential were in RBF network by sigmoid activation function and after this network, RSM had the best amount for energy efficiency, Also for exergy efficiencies, exergy loss and improvement potential obtained acceptable results in MLP network by a linear activation function. The worst amount was at MLP network by tangent hyperbolic. In general, the neural network can have more ability than the response surface method.

Dulce de leche submitted to ohmic heating treatment: Consumer sensory profile using preferred attribute elicitation (PAE) and temporal check-all-that-apply (TCATA)

This study aimed to evaluate the effects of the application of ohmic heating (OH) to milk (0, 2, 4, 6, 8, or 10 V cm^-1, 72-75 °C/15 s) on the sensory profiling of dulce de leche (DL) evaluated using preferred attribute elicitation (PAE) and temporal Check-all-that-apply (TCATA) methodologies. In addition a consumer test was also performed. OH-DL samples presented increased scores for all the sensory attributes evaluated. Low or intermediate strength electric fields contributed to increase bitter taste and decrease DL aroma and sweet taste of the products, without impact on the overall liking. When high strength electric fields were applied, higher brightness, fluidity and DL flavor scores were observed, as well as, lower intensities in consistency and sandiness scores, resulting in increased acceptance by consumers. From TCATA data, it could be observed that the perception of all sensory attributes increased as well as increased the strength of the electric fields. Overall, the adoption of electric fields with higher strength in ohmic heating during DL processing is advised, since they improved the intensity and perception of desirable intrinsic DL sensory attributes as well as improved DL overall liking.

Transportation of heat generation/absorption and radiative heat flux in homogeneous-heterogeneous catalytic reactions of non-Newtonian fluid (Oldroyd-B model)

BACKGROUND

This study addresses the three-dimensional (3D) stagnation point flow of non-Newtonian material (Oldroyd-B) with magnetohydrodynamics. Furthermore, Ohmic heating and radiative flux are used in the modeling of energy expression. The surface is convectively heated. Equal strengths of diffusions for homogeneous and heterogeneous reactions are counted. Results are computed and presented graphically. Heat transfer rate is numerically discussed through table.

METHOD

Here the nonlinear differential system first converted into ordinary differential equation through implementation of appropriate similarity variables. The obtained ordinary system is tackled through homotopy technique for convergent solutions. The outcomes are presented through different graphs and discussed in section six.

OUTCOMES

The remarkable results of the present communication which is obtained from the semi analytical method i.e., "homotopy method" is summarized as (i) Opposite impact is noticed for velocity components i.e., (f'(ξ), g(ξ)) for rising fluid parameter and rotation parameter. (ii) The temperature is direct relation with Biot number and radiative variable. (iii) Heat transfer rate is more versus Biot number and radiation variable. (iv) The concentration field shows opposite impact versus homogeneous and heterogeneous parameters.

Comparison of different ultrasound assisted extraction techniques for pectin from tomato processing waste

Concept of waste to wealth is a hot topic with research ongoing globally to reduce carbon footprint. In an effort to follow up this cause present study focused on tomato industry waste specifically the peel of tomatoes for extraction of pectin. Pectin extraction was performed using five different extraction techniques (Ultrasound assisted extraction (UAE); microwave assisted extraction (MAE); ohmic heating assisted extraction (O_HAE); ultrasound assisted microwave extraction (UAME) and ultrasound assisted ohmic heating extraction (UAO_HE) at different power levels to study its extraction and degradation kinetics and in turn to optimize the extraction process. The extracted pectin yield ranged from 9.30% for O_HAE to 25.42% for MAE. Also, there was very less difference in the yield of MAE and UAME extracted pectin, but at the cost of major difference in degree of esterification 59.76 ± 0.70 and 73.33 ± 1.76%, respectively. In addition, all the pectin extracted under optimized conditions was having acceptable purity, [Galacturonic acid (GalA) content ranged from 675.8 ± 11.31 to 913.3 ± 20.50 g/kg of pectin]. FTIR analysis confirmed the presence of functional groups in the finger print region of identification for polysaccharide in all the extracted pectin. According to obtained results, UAME can be considered as better green extraction technology in terms of extraction yield as well as in quality of pectin compared to the other treatments used. Therefore, results suggest that UAME can be used as an efficient pectin extraction method from tomato processing waste.

Ohmic heating as an innovative approach for the production of keratin films

Ohmic heating is a thermal processing method based on the application of electric fields directly into a semi-conductive medium. In this study, we explored for the first time the use of ohmic heating to obtain keratin films. The properties of the films prepared by ohmic heating and conventional heating were evaluated and compared under similar thermal profiles. A lower increase in free thiols' concentration was obtained for the keratin solutions and keratin films submitted to ohmic heating (16% increase for the keratin solution extracted from virgin hair, pH 9, submitted to ohmic heating and 23% when submitted to conventional heating). Significant differences in the swelling results were observed for the films prepared with keratin extracted from virgin hair, with a swelling decrease in about 55% for the films prepared by ohmic heating. Generally, the keratin films obtained by ohmic heating showed distinct properties comparatively to the films produced by conventional methods. The application of a fusion protein on the keratin films demonstrated their capacity to be used as substitutes to hair fibers when evaluating the potential of new cosmetic products. This work suggests that ohmic heating show potential to tailor keratin films properties depending on an intended application or functionality.

Label free-based proteomic analysis of Escherichia coli O157:H7 subjected to ohmic heating

To investigate the inactivation mechanism of ohmic heating (OH) on Escherichia coli O157:H7 at the same inactivation levels, a label-free quantitative proteomic approach was employed in this study. Quantification of 2633 proteins was obtained with high confidence. Compared to untreated samples (CT), a total of 169, 84, and 26 proteins showed significantly differential abundance after high voltage OH (HVOH, 10 V/cm), low voltage OH (LVOH, 5 V/cm), and water bath heating (WB), respectively. Glyoxylate and dicarboxylate metabolism, ABC transporters, biosynthesis of amino acids, glycerophospholipid metabolism, and ribosome pathway were the main KEGG pathways mediated by OH, but only ribosome pathway was greatly affected by WB. The significant differences in proteome changes of E. coli O157:H7 among HVOH, LVOH, and WB treatments, especially the greater number of differential proteins in HVOH, indicated that OH might exert additional effects on proteome of E. coli O157:H7 due to the electric current, particularly in HVOH with higher electric field. This result enriched our understanding of molecular changes of E. coli O157:H7 induced by OH and provided data reference for further research into the inactivation mechanism of OH.

Ohmic cooking of instant rice cake soup: energy efficiency and textural qualities

The potential of ohmic heating was investigated to cook instant rice cakes according to electric field strengths (9, 12, 15, 18 V/cm) and cooking times (60, 80, 100, 120 s). Customized ohmic heating system was equipped with ohmic cell, electrodes, thermocouple, proportional-integral-differential controller and data acquisition system. Heating rate significantly increased when electric field strengths increased. Heating rate was 12.1 °C/min at 9 V/cm, and was increased to 38.8 °C/min at 18 V/cm. The energy efficiency was evaluated in terms of system performance coefficient (SPC) energy efficiency. The best SPC energy efficiency was 0.65 at an electrical field strength of 18 V/cm. An electric field strength of 15 V/cm and an 80 s cooking time resulted in the most preferable hardness (7.73 N). Ohmic heating would be applicable to cook instant rice cakes, resulting in good energy efficiency and textural qualities.

Application of image analysis technique to determine cleaning of ohmic heating system for milk

Cleaning of equipment is one of the major areas of concern in food industry. Image analysis technique was used to assess the cleaning effectiveness and optimize the CIP protocol for ohmic heating setup. Process parameters selected for optimization of cleaning were caustic concentration (1.0, 1.5, 2.0 and 2.5%), caustic temperature (70, 75, 80 and 85 °C), acid concentration (0.00, 0.25, 0.5 and 0.75%), and acid temperature (40, 50, 60 and 70 °C). Time for caustic treatment was varied from 5 to 20 min at an interval of 5 min, while time acid treatment was kept at a constant of 10 min. Taguchi orthogonal array design was used generate different combinations of acid and alkali concentration and temperature. Images of ohmic heating plates were taken before and after the cleaning procedure. MATLAB program was developed to analyze and extract Gray-Level Co-occurrence (GLCM) matrix properties from the image. Optimized combination was selected based on the highest value of desirability factor among all the experimental set of trials. Treatment with 1.5% caustic concentration at 70 °C for 5 min followed by 0.5% nitric acid concentration at 60 °C was found optimum effective CIP of the heating plates used in ohmic heating setup. GLCM properties correlation, cluster prominence, cluster shade, entropy, homogeneity and inverse difference moment normalized were found suitable for analysis of cleaning effectiveness and optimization of the CIP protocol.

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.

Impact of ohmicsonication treatment on pectinmethylesterase in not-from-concentrate orange juice

The present study investigates the application of ohmicsonication (OS) as a new hurdle technology for pasteurization of Not-from-concentrate orange juice (NFCOJ). OS process parameters to inactivate pectinmethylesterase (PME) activity in NFCOJ were optimized using response surface methodology. The influence of Sonication (S), Thermosonication (TS), Ohmic heating (OH) and OS on inactivation of PME were compared to conventional heat (CH) treatment. Their effects on physical, chemical and microbiological contents were included. In comparison to fresh orange juice, the inactivation of PME was 96%, 95%, 89%, 90% and 29% for OS, OH, TS, CH and S treatments, respectively. Highest cloud value was obtained for OS (1.240 A) treatment. OS treatment gave a lower vitamin C loss compared to TS, OH and CH treatments. A significant increase in the total phenolic content were obtained in the following order OS > TS > OH > CH. OS treated juice also contained the lowest value of hydroxymethyl furfural (0.90 mg/L) compared to OH (0.95 mg/L), TS (1.37 mg/L) and CH (2.72 mg/L) treated samples. Overall, the results indicated that OS can be integrated as a substitute to pasteurization of NFCOJ.

Mechanisms of enhanced bacterial endospore inactivation during sterilization by ohmic heating

During ohmic heating, the electric field may additionally inactivate bacterial endospores. However, the exact mechanism of action is unclear. Thus, a mechanistic study was carried out, investigating the possible target of electric fields inside the spore. Bacillus subtilis spores were heated by conventional and ohmic heating in a capillary system under almost identical thermal conditions. Wild-type (PS533) spores were used, as well as isogenic mutants lacking certain components known for their contribution to spores' heat resistance: small-acid soluble proteins (SASP) protecting DNA (PS578); the coat covering the spore (PS3328); and the spore germination enzyme SleB (FB122(+)). Treatment-dependent release of the spore core's depot of dipicolinic acid (DPA) was further evaluated. Up to 2.4 log₁₀ additional inactivation of PS533 could be achieved by ohmic heating, compared to conventional heating. The difference varied for the mutants, with a decreasing difference indicating a decreased effect of the electric field and vice versa. In particular, mutant spores lacking SASPs showed a behavior more similar to thermal inactivation alone. The combination of heat and electric field was shown to be necessary for enhanced spore inactivation. Thus, it is hypothesized that either the heat treatment makes the spore susceptible to the electric field, or vice versa.

Processing raspberry-flavored whey drink using ohmic heating: Physical, thermal and microstructural considerations

The effect of ohmic heating processing (10, 100, 1000 Hz - 25 V;45, 60, 80 V - 60 Hz until 65 °C-30 min) on physical (color, rheology, particle size diameter), thermal (differential scanning calorimetry, DSC), physicochemical (time domain nuclear magnetic resonance, TD-NMR) and microstructural (optical microscopy) properties of raspberry-flavored whey drink was investigated. The samples were submitted to an ohmic system and conventional pasteurization (65 °C-30 min). Both processing led to increases in the color parameters (C*, h* and ∆E*) in the first 30 min. For the treatments, 10 Hz-25 V and 1000 Hz-25 V, more viscous, and consequently increased D[4,3] and D[3,2] values were observed, and similar results were obtained for the DSC behavior. The microstructure confirmed aggregation of cell structure in those configurations (10 Hz and 1000 Hz-25 V). OH, parameters for both ohmic configurations have an impact in all the evaluated parameters for raspberry-flavored whey drink, which can be interesting for the dairy industry.

Second Law Analysis of Unsteady MHD Viscous Flow over a Horizontal Stretching Sheet Heated Non-Uniformly in the Presence of Ohmic Heating: Utilization of Gear-Generalized Differential Quadrature Method

In this article, the entropy generation characteristics of a laminar unsteady MHD boundary layer flow are analysed numerically for an incompressible, electrically conducting and dissipative fluid. The Ohmic heating and energy dissipation effects are added to the energy equation. The modelled dimensional transport equations are altered into dimensionless self-similar partial differential equations (PDEs) through suitable transformations. The reduced momentum and energy equations are then worked out numerically by employing a new hybrid method called the Gear-Generalized Differential Quadrature Method (GGDQM). The obtained numerical results are incorporated in the calculation of the Bejan number and dimensionless entropy generation. Quantities of physical interest, like velocity, temperature, shear stress and heat transfer rate, are illustrated graphically as well as in tabular form. Impacts of involved parameters are examined and discussed thoroughly in this investigation. Exact and GGDQM solutions are compared for special cases of initial unsteady flow and final steady state flow. Furthermore, a good harmony is observed between the results of GGDQM and those given previously by the Spectral Relaxation Method (SRM), Spectral Quasilinearization Method (SQLM) and Spectral Perturbation Method (SPM).

Effect of Ohmic heating on functionality of sodium caseinate - A relationship with protein gelation

Sodium caseinate (NaCAS) is widely used in the food industry to provide nutritional and functional benefits. This work deals with the effects of applying moderate electric fields (MEF) of different intensity - ranging from 2 V·cm^-1 to 17 V·cm^-1 - on the physical and functional properties of NaCAS solutions during Ohmic heating (OH) at 95 °C. Self-standing gels were produced regardless the heating technique applied (i.e. conventional or OH), and these gels were much more prone to physical rupture when compared with the ones produced from unheated NaCAS. Interestingly, OH treatment formed gels with lower values of strain at rupture and water holding capacity than unheated samples; this pattern was not observed for gels obtained through the conventional heating treatment (at 0 V·cm^-1). These effects may be linked with disturbances of the distribution of random coil structures and enhanced solubility of NaCAS at its isoelectric point, reducing aggregation and impairing the development of a more compact protein network. Results show that OH presents potential to be used as volumetric heating tool for NaCAS solubilization and for the production of distinctive acidified systems.

Changes on the phytochemicals profile of instant corn flours obtained by traditional nixtamalization and ohmic heating process

We studied the changes in the phytochemicals profile of two instant corn flours produced by different process: traditional nixtamalization process (TN) and by ohmic heating process (OH). The highest total phenolics content was found in the OH flours (OHF), which showed predominance of bound phenolics and free flavonoids compared with the TN flours (TNF). Ferulic acid measured by HPLC-DAD was the most abundant compound in its bound form in the OHF, but decreased by 57% in TNF. The insoluble fiber content was preserved by the OHF (17.49%) and the soluble fiber increased ∼65% compared with TNF. These data suggest that instant corn flours processed by OH preserves the phenolic profile and antioxidant profile similarly than flours processed by TN; furthermore, water waste was reduced significantly, and no effluents were produced in the ohmic heating process.

Application of ohmic heating for concentration of milk

The concentration of milk through evaporation is the most commonly employed unit operation for the production of a wide array of traditional and industrial dairy products. Major problems associated with thermal evaporation are a loss of aroma, flavor and color change. Ohmic heating (OH) has an immense potential for rapid and uniform heating of liquid, semi-solid and particulate foods, yielding microbiologically safe and high-quality product. The effect of ohmic heating on physico-chemical, rheological, sensorial and microbial properties during concentration of cow milk, buffalo milk and mixed milk (50:50) was studied and compared to conventional evaporation. OH significantly increased free fatty acids (FFA), apparent viscosity, hydroxymethylfurfural (HMF) content, instrumental color values i.e. redness (a*) and yellowness (b*) values. However, pH value and whiteness (L*) of the concentrated milk decreased significantly. OH caused a drastic reduction in microbiological counts and treated milk can be kept for a longer period.

Influence of sucrose concentration on electric conductivity of banana pulp during ohmic heating

Ohmic heating is a substitutive rapid heating method for food products. In this study, banana pulp with different concentrations of sugar is ohmically heated and the influence of sucrose concentration on electrical conductivity was investigated. The electrical conductivity, pH, total soluble solids, acidity, ascorbic acid content before and after ohmic heat treatment were also analysed. As the sucrose concentration increased, heating time at various voltage gradients 13.33, 20 and 26.66 V/cm increased, and the electrical conductivity decreased. As the voltage gradient increased, the pH and TSS of treated pulp with different sugar concentration increased followed by decrease in colour and acidity.

Inactivation of Microorganisms in Foods by Ohmic Heating: A Review

Ohmic heating (OH) is an alternative food processing technology for effectively inactivating microorganisms that depends on the heat that has been generated when electrical current passes directly through food material. The advantages of OH for microbial inactivation include shorter heating time, more uniform heat distribution inside food, reduced nutrition losses, and higher energy efficiency. This review presents some published information regarding the inactivation of microorganisms by OH, including the major factors that influence the inactivation effectiveness of OH, the inactivation of vegetative cells and spores in foods by OH, the inactivation mechanisms of OH, and the challenges and prospects of OH for food processing. This information will improve the understanding of OH for inactivation of microorganisms and promote the application of OH in the food industry.

Optimization of ohmic heating parameters for polyphenoloxidase inactivation in not-from-concentrate elstar apple juice using RSM

In this study, optimization of ohmic heating (OH) process parameters (temperature and voltage gradient) to inactivate polyphenoloxidase (PPO) of not-from-concentrate (NFC) apple juice was conducted. Response surface methodology was used for optimization of OH parameters, where the voltage gradient and temperature on the PPO activity in the NFC apple juice was evaluated. Then the optimized condition was used to produce the NFC apple juice and the quality parameters were evaluated and compared to NFC apple juice prepared by conventional heating (CH). The studied parameters were: PPO activity, total phenolic, total carotenoids, ascorbic acid, cloud value, color as well as physical properties (i.e., TSS, acidity, electric conductivity and viscosity). The reduction of PPO activities was 97 and 91% for OH (at 40 V/cm and 80 °C) and CH (at 90 °C and 60 s), respectively. The reduction of the ascorbic acid was 66.8% for OH significantly lower than the 80% for CH treated samples. The total extracted phenolic content was increased by 5.4 and 2.5% with OH and CH treatments, respectively. The decrease in the concentration of total carotenoids for OH (13.17%) was significantly lower than for CH (34.23%). The color values (L*, a*, b* and ΔE) were only significantly increased in the OH treatment. OH is a potential mild thermal treatment in the production of apple juice with improved functional properties instead of conventional methods.

Electric field-based technologies for valorization of bioresources

This review provides an overview of recent research on electrotechnologies applied to the valorization of bioresources. Following a comprehensive summary of the current status of the application of well-known electric-based processing technologies, such as pulsed electric fields (PEF) and high voltage electrical discharges (HVED), the application of moderate electric fields (MEF) as an extraction or valorization technology will be considered in detail. MEF, known by its improved energy efficiency and claimed electroporation effects (allowing enhanced extraction yields), may also originate high heating rates - ohmic heating (OH) effect - allowing thermal stabilization of waste stream for other added-value applications. MEF is a simple technology that mostly makes use of green solvents (mainly water) and that can be used on functionalization of compounds of biological origin broadening their application range. The substantial increase of MEF-based plants installed in industries worldwide suggests its straightforward application for waste recovery.

Convective thermal and concentration transfer effects in hydromagnetic peristaltic transport with Ohmic heating

The primary theme of this communication is to employ convective condition of mass transfer in the theory of peristalsis. The magnetohydrodynamic (MHD) peristaltic transport of viscous liquid in an asymmetric channel was considered for this purpose. Effects of Ohmic heating and Soret and Dufour are presented. The governing mathematical model was expressed in terms of closed form solution expressions. Attention has been focused to the analysis of temperature and concentration distributions. The graphical results are presented to visualize the impact of sundry quantities on temperature and concentration. It is visualized that the liquid temperature was enhanced with the enhancing values of Soret-Dufour parameters. The liquid temperature was reduced when the values of Biot number were larger. It is also examined that mass transfer Biot number for one wall has no impact on transfer rate. Different mass transfer Biot numbers generate a non-uniform concentration profile throughout the channel cross section.

2-Furoylmethyl amino acids as indicators of Maillard reaction during the elaboration of black garlic

This study reports the formation of 2-furomethyl-amino acids (2-FM-AA) as indicators of Maillard reaction (MR) in black garlic elaboration, followed by the determination of furosine by ion-pair RP-HPLC-UV. The method was assessed for accuracy, repeatability and detection and quantitation limits indicating its adequacy. Traditional procedure of black garlic obtainment and the inclusion of convective drying (CDP) and ohmic heating (OHP) were assayed. For comparison purposes, three commercial black garlic samples were used. Together with furosine (2-FM-lysine), 2-furoylmethyl-γ-aminobutyric acid and 2-FM-arginine were detected. Levels of furosine were higher in CDP (46.6-110.1mg/100g protein) than in OHP (13.7-42.0mg/100g protein) samples, probably due to the most severe processing conditions used in the former. These results highlight the suitability of 2-FM-AA as chemical indicators to monitor the process of black garlic elaboration in order to obtain high quality products.

Investigation of optimum ohmic heating conditions for inactivation of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes in apple juice

BACKGROUND

Control of foodborne pathogens is an important issue for the fruit juice industry and ohmic heating treatment has been considered as one of the promising antimicrobial interventions. However, to date, evaluation of the relationship between inactivation of foodborne pathogens and system performance efficiency based on differing soluble solids content of apple juice during ohmic heating treatment has not been well studied. This study aims to investigate effective voltage gradients of an ohmic heating system and corresponding sugar concentrations (°Brix) of apple juice for inactivating major foodborne pathogens (E. coli O157:H7, S. Typhimurium, and L. monocytogenes) while maintaining higher system performance efficiency.

RESULTS

Voltage gradients of 30, 40, 50, and 60 V/cm were applied to 72, 48, 36, 24, and 18 °Brix apple juices. At all voltage levels, the lowest heating rate was observed in 72 °Brix apple juice and a similar pattern of temperature increase was shown in18-48 °Brix juice samples. System performance coefficients (SPC) under two treatment conditions (30 V/cm in 36 °Brix or 60 V/cm in 48 °Brix juice) were relatively greater than for other combinations. Meanwhile, 5-log reductions of the three foodborne pathogens were achieved after treatment for 60 s in 36 °Brix at 30 V/cm, but this same reduction was observed in 48 °Brix juice at 60 V/cm within 20 s without affecting product quality.

CONCLUSIONS

With respect to both bactericidal efficiency and SPC values, 60 V/cm in 48 °Brix was the most effective ohmic heating treatment combination for decontaminating apple juice concentrates.

Continuous ohmic heating of commercially processed apple juice using five sequential electric fields results in rapid inactivation of Alicyclobacillus acidoterrestris spores

Spores of Alicyclobacillus acidoterrestris, a spoilage bacterium, cause problems for the apple juice industry because they are resistant to thermal treatment. Here, we examined the sporicidal effect of an ohmic heating (OH) system with five sequential electric fields and compared it with that of conventional heating. Apple juice product (50kg) inoculated with A. acidoterrestris spores were subjected to OH (electric field strength=26.7V/cm; frequency=25kHz) at 85-100°C for 30-90s. The effect of conventional heating was also examined under these conditions. OH treatment at 100°C for 30s resulted in total inactivation of the inoculum, with no recovery of viable cells (initial population=4.8-4.9logCFU/ml), whereas 3.6-4.9logCFU/ml of the spores survived conventional heating. OH did not alter the quality (°Brix, color, and pH) of commercial apple juice (p>0.05). These results suggest that the OH system is superior to conventional heating for rapid sterilization (30s) of apple juice to assure microbiological quality in the absence of chemical additives.

Effects of Ohmic Heating, Including Electric Field Intensity and Frequency, on Thermal Inactivation of Bacillus subtilis Spores

Methods for microbial inactivation are important in the food industry; however, conventional external heating (CH) reduces food quality. Accordingly, the nonthermal effects of ohmic heating (OH) on Bacillus subtilis spores in a sodium chloride aqueous solution at 101°C (i.e., the boiling point), as well as the effects of electric field intensity and frequency during OH, were investigated. Survival kinetics were compared between OH and external CH. The inactivation effect on B. subtilis was greater for all electric field conditions (5, 10, and 20 V/cm) than for CH. In particular, 20 V/cm showed a significantly higher inactivation effect (P < 0.05) on B. subtilis than those of CH at 8, 10, 12, 14, and 16 min. The survival data were fitted to various primary kinetic models. In the Weibull model and the log-linear model, there were significant differences (P < 0.05) in the rate parameters δ and k_max between OH at 20 V/cm and CH. However, there were no significant differences (P > 0.05) in survival kinetics between 20, 40, and 60 kHz; B. subtilis spores were inactivated more efficiently as the frequency increased. B. subtilis spores were almost completely inactivated at 14 to 16 min for the 60-kHz treatment, but spores were still alive at 20 and 40 kHz for the same treatment times. These results demonstrated that OH inactivates B. subtilis spores more effectively than CH. OH conditions with high electric field intensities and high frequencies resulted in efficient B. subtilis spore inactivation.

Effect of Power Levels on Inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in Tomato Paste Using 915-Megahertz Microwave and Ohmic Heating

The effect of power levels on inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in tomato paste was investigated using 915-MHz microwave heating (MW) and ohmic heating (OH). Heating uniformity, pathogen inactivation, and quality aspects were determined with 1.8-, 2.1-, 2.4-, and 3.0-kW MW and corresponding OH. GInaFit was used to analyze pathogen inactivation. The heating uniformity of MW-treated samples was inferior to that of OH-treated samples at low power levels of 1.8 to 2.4 kW but improved as the power level increased. Pathogen inactivation of MW-treated samples was significantly higher than that of OH-treated samples at low power levels of 1.8 to 2.4 kW (P < 0.05) but was not significantly different at the highest power level of 3.0 kW (P > 0.05). Quality aspects (color, pH, and lycopene content), except for L*, of MW-treated samples were not significantly degraded (P > 0.05) by increased power levels. Our results indicate that increasing power levels of MW ensures heating uniformity and microbiological safety and preserves quality aspects of tomato paste.

Studies on the effect of ohmic heating on oil recovery and quality of sesame seeds

This research describes a new technological process for sesame oil extraction. The process deals with the effect of ohmic heating on enhancement of oil recovery and quality of cleaned and graded sesame seed. The effect of ohmic heating parameters namely electric field strength (EFS), end point temperature (EPT) and holding time (HT) on oil extraction process were investigated. Three levels of electric field strength (600, 750 and 900 V/m), end point temperature (65, 75 and 85 °C) and holding time (5, 10 and 15 min.) were taken as independent variables using full factorial design. Percentage oil recovered from sesame seed through mechanical extracted oil by application of ohmic heating varies from 39.98 to 43.15 %. The maximum oil recovery 43.15 % was obtained when the sample was heated and maintained at 85 °C using EFS of 900 V/m for a holding time of 10 min as against 34.14 % in control sample. The free fatty acid (FFA) of the extracted oil was within the acceptable limit (1.52 to 2.26 % oleic acid) of 0.5 to 3 % as prescribed respectively by Prevention of Food Adulteration (PFA) and Bureau of Indian Standards (BIS). The peroxide value of extracted oil was also found within the acceptable limit (0.78 to 1.01 meq/kg). The optimum value for maximum oil recovery, minimum residual oil content, free fatty acid (FFA) and peroxide value were 41.24 %, 8.61 %, 1.74 % oleic acid and 0.86 meq/kg, respectively at 722.52 V/m EFS at EPT 65 °C for 5 min. holding time which was obtained by response surface methodology.

Mathematical modeling and microbiological verification of ohmic heating of a multicomponent mixture of particles in a continuous flow ohmic heater system with electric field parallel to flow

To accomplish continuous flow ohmic heating of a low-acid food product, sufficient heat treatment needs to be delivered to the slowest-heating particle at the outlet of the holding section. This research was aimed at developing mathematical models for sterilization of a multicomponent food in a pilot-scale ohmic heater with electric-field-oriented parallel to the flow and validating microbial inactivation by inoculated particle methods. The model involved 2 sets of simulations, one for determination of fluid temperatures, and a second for evaluating the worst-case scenario. A residence time distribution study was conducted using radio frequency identification methodology to determine the residence time of the fastest-moving particle from a sample of at least 300 particles. Thermal verification of the mathematical model showed good agreement between calculated and experimental fluid temperatures (P > 0.05) at heater and holding tube exits, with a maximum error of 0.6 °C. To achieve a specified target lethal effect at the cold spot of the slowest-heating particle, the length of holding tube required was predicted to be 22 m for a 139.6 °C process temperature with volumetric flow rate of 1.0 × 10(-4) m3/s and 0.05 m in diameter. To verify the model, a microbiological validation test was conducted using at least 299 chicken-alginate particles inoculated with Clostridium sporogenes spores per run. The inoculated pack study indicated the absence of viable microorganisms at the target treatment and its presence for a subtarget treatment, thereby verifying model predictions.

The process of producing tomato paste by ohmic heating method

In this study, the effect of ohmic heating technique on electrical conductivity, water evaporation rate, heating rate, colour parameters, pH and energy consumption of tomato samples was investigated. Ohmic heating was accomplished till the moisture content of the tomato samples reduced from initial moisture content of as 9.33 (dry basis) to a safer level of 2.2. The results of the nonlinear mathematical model including the effects of voltage gradient level and the temperature on the electrical conductivity changes had good agreement (R ≥ 0.955) with the experimental data. Also, it was observed that the electrical conductivity increased along with concentration of tomato samples. The range of electrical conductivity during ohmic heating was 3.19-8.95 (S/m). It was found that processing time decreased from 28.32 to 4.3 min over the voltage gradient range studied (6 to 14 V/cm), which resulted in decreased specific energy consumption from 4.63 to 3.05 (MJ/kg water). Due to increasing of heating rate and water evaporation rate at high voltage gradient, the change of the pH was limited. Samples processed in high voltage gradient had higher L*, b* and hue angle (h), lower a* and Chroma (C) values as compared to low voltage gradient. The optimum value of processing time, pH, colour, specific energy consumption was obtained at 14 V/cm voltage gradient level.

Innovative food processing technology using ohmic heating and aseptic packaging for meat

Since the Tohoku earthquake, there is much interest in processed foods, which can be stored for long periods at room temperature. Retort heating is one of the main technologies employed for producing it. We developed the innovative food processing technology, which supersede retort, using ohmic heating and aseptic packaging. Electrical heating involves the application of alternating voltage to food. Compared with retort heating, which uses a heat transfer medium, ohmic heating allows for high heating efficiency and rapid heating. In this paper we ohmically heated chicken breast samples and conducted various tests on the heated samples. The measurement results of water content, IMP, and glutamic acid suggest that the quality of the ohmically heated samples was similar or superior to that of the retort-heated samples. Furthermore, based on the monitoring of these samples, it was observed that sample quality did not deteriorate during storage.

Ohmic pre-drying of tomato paste

In this study, the effects of ohmic pre-drying technique on moisture ratio, drying rate, drying time, specific energy consumption, drying efficiency, and effective moisture diffusivity of tomato paste were investigated. Pre-drying experiments were carried out in an ohmic laboratory dryer at voltage gradient levels of 6, 8, 10, 12, 14, and 16 V/cm and oven at 105  and 1.0 m/s air velocity (control sample). Pre-drying was accomplished till the moisture content of the tomato paste reduced from initial moisture content of 90% (w.b.) to a safer level of 70% (w.b.). The ohmic pre-drying reduced the drying time of tomato paste by 80-97%, compared with the hot air drying. Pre-drying took place mainly in warming up, constant rate, and falling rate periods. Six available moisture-ratio models were fitted to the pre-drying data. The results showed that the Midilli et al. model is the most appropriate model for pre-drying behavior of tomato paste. The effective moisture diffusivity varied from 5.39 × 10(-8) to 3.91 × 10(-7)m(2)/s with an activation energy of 2.082 (V/g.cm). Both specific energy consumption and drying efficiency were considerably enhanced by increasing voltage gradient. It was found that the specific energy consumption and drying efficiency varied from 3.72 to 2.29 MJ/kg water and 67.8 to 83.8%, respectively.

Ohmic heating as a pre-treatment in solvent extraction of rice bran

Rice bran, which is one of the major by products of paddy contain high quality proteins and edible oil apart from fibre, ash and NFE (nitrogen free extract). The existing solvent extraction method employs n-hexane as the most viable solvent for the extraction of oil from rice bran. But the high cost and scarce availability of n-hexane resulted in uneconomical extraction of rice bran oil. In this study, rice bran was ohmically heated for different time periods(1, 2 and 3 min) with different current values (5, 15 and 20 A) and with different concentration of sodium chloride (1 M, 0.1 M and 0.01 M) as conducting medium. The ohmically heated rice bran was subjected to extraction studies. Ohmic heating of rice bran of paddy varieties Red Triveni and Basmati reduced the extraction time by nearly 75 % and 70 % respectively and gave a maximum quantity of oil extracted when compared to bran, which was not ohmically heated. From the experiments with varying concentrations, residence time of ohmic heating and currents, it was found that ohmically heating the rice bran with 1 M sodium chloride solution and with a current value of 20 A for 3 min gave maximum oil extraction with minimum extraction time.

Technology, applications and modelling of ohmic heating: a review

Ohmic heating or Joule heating has immense potential for achieving rapid and uniform heating in foods, providing microbiologically safe and high quality foods. This review discusses the technology behind ohmic heating, the current applications and thermal modeling of the process. The success of ohmic heating depends on the rate of heat generation in the system, the electrical conductivity of the food, electrical field strength, residence time and the method by which the food flows through the system. Ohmic heating is appropriate for processing of particulate and protein rich foods. A vast amount of work is still necessary to understand food properties in order to refine system design and maximize performance of this technology in the field of packaged foods and space food product development. Various economic studies will also play an important role in understanding the overall cost and viability of commercial application of this technology in food processing. Some of the demerits of the technology are also discussed.