Radio Frequency Heating Research Articles

Effect of radio frequency energy combined with natamycin on Aspergillus niger survival and quality of dried shiitake mushroom with different moisture content

Effectively controlling molds in dried shiitake mushrooms is important for food industry to maintain the product quality. To improve the edible safety of shiitake mushrooms, this study applied radio frequency (RF) energy combined with natamycin to inactivate Aspergillus niger spores, and evaluate the quality changes after the treatment. The results showed that the population of A. niger spores in shiitake mushrooms with different moisture contents (MCs) could achieve a 5-log (CFU/g) reduction after the combined treatment at different temperatures. Weibull distribution (R2 = 0.978 to 1.000) provided a better fit for the inactivation kinetics of A. niger spores than Linear model (R2 = 0.954 to 0.990) and Logistic one (R2 = 0.953 to 0.988). Meanwhile, the three-dimensional inactivation curves were constructed based on the sample MCs, RF heating time, and holding time. In addition, the MCs of treated shiitake mushrooms decreased by 4.12%–7.66% (w.b.) after natural cooling, achieving synchronous drying. There was no significant difference in textural properties of shiitake mushrooms after the combined treatment. The changes in color, structure, rehydration ratio, and total sugar content were affected by the treatment time and temperatures. As one of the main aroma substances, the content of sulfur-containing compounds in shiitake mushrooms after treatment increased compared to that of the control samples. This study indicates that the combination of RF energy and natamycin is feasible for inactivating pathogens in shiitake mushroom and ensuring the safety of their consumption.

The Influence of Radiofrequency Heating on the Quality and Shelf of Life of Pepper

Pepper is one of the common vegetable food items that constitute most African dishes with beneficial health properties. This study investigates the influence of radiofrequency (RF) heating on the quality and shelf life of pepper. Utilising the measured dielectric properties of pepper, the research evaluates how microwave exposure at varying frequencies affects pepper's nutritional content and preservation duration. Fresh samples of pepper were subjected to radio waves ranging from 5 MHz to 25 MHz, and their dielectric properties, proximate composition, and shelf life were analysed. The dielectric properties were measured using a parallel plate capacitance method, revealing significant variations in conductivity, dielectric constant, and loss factor across different frequencies. Results demonstrated that RF treatment effectively extended the shelf life of pepper, with the highest frequency (25 MHz) achieving a shelf life of 36 days, compared to 20 days for the control. Moreover, the study observed minimal changes in the proximate composition of pepper, ensuring the retention of its nutritional quality. This research provides valuable insights into the use of RF heating as a viable technique for extending the shelf life of pepper while maintaining its nutritional integrity.

Numerical modeling and parametric analysis of temperature distribution in soil based on water content variation under radio frequency heating for in-situ thermal remediation

Radio frequency heating (RFH) is recognized as an efficient and economical method for volatilizing organic pollutants from contaminated soils. Although some numerical simulations have been conducted to predict temperature changes during RFH, models that account for effects of water content (WC) variation on dielectric properties and temperature evolution in soil were rarely reported. To address this, a three-dimensional numerical model integrating electromagnetic-thermal conversion, heat transfer, and mass transfer was developed with coupling dynamic changes in WC and corresponding impacts on soil properties. The effects of soil types and RFH engineering parameters on temperature evolution and energy utilization were evaluated. The model's temperature prediction was validated using experimental data, indicating that temperature decreases outward from hot electrode, with high-temperature regions forming at the top and bottom regions near electrode. Water evaporation in soil causes a temperature plateau with >76.25 % of energy utilized for heating and evaporating water during 60-d RFH. Moreover, higher soil WC could increase electromagnetic-thermal conversion capability, counteracting the negative impact of increased specific heat capacity on temperature rise. Thermophysical properties of soil are crucial in RFH: sand, with lower specific heat capacity and higher thermal conductivity, results in faster heating rates. While, clay, with higher density and specific heat capacity, results in lower heating rates but greater energy utilization efficiency. Low-power RHF and wider well spacing improve the uniformity of temperature distribution but require more time to reach target temperatures. Moreover, input power influences the magnitude and timing of optimal energy utilization efficiency, while well spacing primarily affects timing. The models developed in this study provide essential guidance for RFH-based soil remediation projects.

Influence of the induced Na+/Cl- ionic polarization effects on multi-scale structures of maize starch during radio frequency heating.

Structural modification/unfolding of starch molecules can be improved by radio frequency (RF) treatment. This necessitates a better understanding of its action mechanism through rapid heating and dipolar/ionic molecular vibration effects. Native maize starch (NS) was subjected to RF heating in a NaCl solution to five target temperatures, and its effect on structural modifications was evaluated. Results showed that the conductivity, particle size distribution and zeta potential of RF heated starch increased with increasing temperature. RF energy had a significant effect on the vibration intensity of other skeleton modes. No new chemical bonds/groups were formed in the starch even though there was the effect of sodium/chloride ions with the added vibration intensity of the ions and the dipolar rotation movements resulted in changes in the disordered and/or ordered structures. The RF treatment at 70 °C had the highest energy (10.4 kJ) of inter-strand hydrogen bond, crystallinity (36.6 %) and trough viscosity (2480 cp), but had the lowest crystallite dimension (13.7 nm), full width at half maximum (14.4) of peak at 480 cm-1, and breakdown (534 cp) and setback (784 cp) viscosities based on X-ray diffraction, Fourier transform infrared, and Raman and RVA observations.

Radio frequency inactivation of Bacillus cereus and natural microbiota in brown rice: Evaluation of inactivation kinetics and germination capacity

Brown rice and its sprout are prone to be contaminated by foodborne pathogens, resulting in potential safety issues. Effective pasteurization methods rely on the thermal death kinetics of the targeted microorganisms and gemination rate of brown rice. This study investigated the influence of five temperature and four moisture content (MC) levels on inactivation kinetics of Bacillus cereus or native microbiota and germination capacity changes of brown rice by radio frequency (RF) heating using first-order, Weibull and Biphasic models. Results showed that increasing MC and treatment temperature greatly enhanced the inactivation of B. cereus but excessive temperature (>75 °C) impaired seed physiology and reduced germination capacity of brown rice. The selected RF treatment (85 °C for 20 min and 80 °C for 30 min for samples with 14.2 % w.b., 75 °C for 30 min, 80 °C for 20 min, and 85 °C for 5 min for samples with 16.2 % w.b.) could reduce the populations of B. cereus by approximately 4.0 log CFU/g, whereas the reductions in total bacteria, yeasts and molds were less than 3.0 log CFU/g. Compared with the first-order linear model and Biphasic model, Weibull model provided the better fitted inactivation kinetics with superior statistical values (R2: 0.944–0.999; RMSE: 0.002–0.879) and validation indices (accuracy factor: 1.003–1.034; bias factor: 0.991–1.025) at all MCs and temperatures. The established Weibull model may offer a reliable method for fitting the inactivation kinetics of B. cereus in brown rice and would help the grain industry to develop effective RF pasteurization protocols.

Reinterpreting radio frequency heating and current drive theory in a tokamak

Quasilinear treatments are widely used for tokamaks to evaluate radio frequency (rf) heating and current drive. Even though the core of a tokamak plasma is weakly collisional, the solution of the linearized kinetic equation is evaluated using unperturbed collisionless trajectories while often treating successive poloidal circuits of the passing (and trapped) particles as uncorrelated or nearly so. In addition, the most important effect of tokamak geometry, the mirror force, is usually mistreated or ignored when obtaining the solution. These concerning aspects of rf treatments are clarified by considering lower hybrid heating and current drive to illustrate that the electrons in resonance with the applied rf are enclosed by narrow collisional boundary layers, and that tokamak geometry makes it necessary to retain poloidal variation when solving a weakly collisional linearized kinetic equation. Other aspects such as collisional boundary layers at the trapped–passing boundary, cyclotron resonances, and the limitations of quasilinear theory are also considered. The new insights lead to a fundamentally different formulation and interpretation of the solution of the linearized Fokker–Planck equation used for rf quasilinear theory in a tokamak, while retaining many of the features that have contributed to its successful application to rf heating and current drive.

Investigation of Coupling Effect for Adjacent Orthopedic Implants on MRI Radio-Frequency Heating

This paper investigates the mechanism of radio-frequency (RF) heating that occurs when two adjacent orthopedic implants are present together under magnetic resonance imaging (MRI) at 1.5 Tesla and 3.0 Tesla. When a patient has multiple implants close to each other, interactions between the implants may increase RF heating. Typical generic interlocking plate and antibiotic nail implants are adopted as examples. To analyze the effect of adjacent implants, the amplitude and direction of incident and scattering vector electric fields at the hot spot position are calculated and extracted using numerical simulation based on Huygens principle. It is shown that a strong coupling effect occurs due to the existence of both the incident field and a strong scattering field. Huygens principle can be used to obtain the first and second order scattering fields generated between implants. If the first- and second-order electric field terms are summed within a certain region, the RF-induced heating of this dual-implant system increases.

Radio frequency-only thermal processing of skimmed milk powder: Case study on the influence of RF heating profile on quality and Salmonella Typhimurium inactivation.

Radio frequency (RF) is a dielectric heating technology that allows rapid and volumetric heating of milk powder, outperforming the heating uniformity of conventional powder heating methods. Typically, RF milk powder processing consists of a fast RF heating phase, followed by an oven heating phase in temperatures around 90 °C. This methodology can result in milk powder quality deterioration due to non-uniform temperature distributions and local overheating. Radio frequency-only processes with a more gradual heating rate are alternative solutions to minimise the impact on milk powder quality. This study investigated the effect of the heating rate on the microbial inactivation of Salmonella Typhimurium inoculated in skimmed milk powder, as well as the effect of each process on two quality characteristics, colour and solubility. Overall, a slower heating profile resulted in sufficient inactivation rates of Salmonella in skimmed milk powder, while still providing a high-quality end product. A 4-log reduction was achieved by treating the skimmed milk powder up to 95 °C using a slower, longer heating rate. No statistically significant changes were observed in the solubility of skimmed milk powder and only the harshest treatment to 95 °C led to a slight increase in the yellowness of the skimmed milk powder colour.

In-pack radio frequency heating of liquid whole egg: Effect of agitation on heating rate and uniformity

In-pack radio frequency (RF) heating of liquid whole egg (LWE) was performed using a 27.12 MHz parallel-plate radio frequency (RF) system. To do this, 600 mL of LWE was subjected to RF heating in a RF-transparent plastic bag (140 mm×180 mm). Experiments were conducted at two different electrode gap settings (98 and 103 mm) with and without orbital movement in the horizontal plane. The effect of agitation on heating rate and uniformity was investigated for varying rpm’s (120 and 140 rpm) for a constant orbit diameter (35 mm). An orbital shaker was specially designed and coupled with the RF system for this purpose. Fiber optic probes were used to continuously measure the temperature of LWE at four different internal locations. Temperature uniformity index (TUI) was calculated to evaluate the uniformity of heating. Coagulation of LWE around the headspace was inevitable when the package was stationary during the treatment. Agitation brought about by orbital movement prevented the coagulation. Drastic improvement in heating rate and uniformity was observed upon orbital movement of LWE at all conditions.

Mushroom polyphenol oxidase inactivation kinetics and structural changes during radiofrequency heating

The effects of radiofrequency (RF) heating on the activity, structure, and surface hydrophobicity of mushroom polyphenol oxidase (PPO) were examined and four kinetic models of inactivation (First-order model, Weibull model, Logistic model and Bi-phasic model) were fitted. The results demonstrated that RF heating could effectively inactivate PPO, logistic and Bi-phasic model attained the best fit. The circular dichroism (CD) and fluorescence spectroscopy spectra revealed that RF heating at 65 °C for 180 s caused changes in the secondary and tertiary structures of PPO, reducing the α-helix content from 38.5% to 30.3% and red-shifting the emission peak wavelength of the maximum fluorescence intensity from 318 nm to 321 nm. RF heating also caused a significant enhancement of the surface hydrophobicity of the PPO (P < 0.05). The color test results showed that RF heating could inhibit the browning of mushrooms (P < 0.05). Thus, RF heating is an effective technique for the inactivation of enzymes and further research should be performed on RF heating applications to inactivate enzymes in the food industry.

The exploration of pasteurization processes and mechanisms of inactivation of Bacillus cereus ATCC 14579 using radio frequency energy

Radio frequency (RF) heating has been utilized to investigate sterilization techniques, but the mechanism of sterilization via RF heating, particularly on Bacillus cereus (B. cereus), has not been thoroughly examined. In this paper, sterilization processes and potential bactericidal mechanisms of B. cereus using RF were investigated. The best heating and sterilization efficiency was achieved at (Electrode gap 130 mm, conductivity of bacterial suspension 0.1 S/m, volume of bacterial suspension 40 mL). Heating a suspension of B. cereus to 90 °C in 80 s using RF reduced the number of viable bacteria by 4.87 logarithms. At the cellular level, there was a significant leakage of nucleic acids and proteins from the bacterial cells. Additionally, the integrity of the cell membrane was severely damaged, with a decrease in ATP concentration of 2.08 mM, Na, K-ATPase activity to 10.7 (U/109 cells), and Ca, Mg-ATPase activity to 11.6 (U/109 cells). At the molecular level, transcriptomics analysis showed that RF heating of B. cereus to 65 °C produced 650 more differentially expressed genes (DEGs) compared with RF heating to 45 °C. The GO annotation analysis indicated that the majority of differentially expressed genes (DEGs) were predominantly associated with cellular components. KEGG metabolic analysis showed enrichment in microbial metabolism in diverse environments, etc. This study investigated the potential bactericidal mechanism of B. cereus using RF, and provided some theoretical basis for the research of the sterilization of B. cereus.

Effect of Thermal Processing on Food Allergenicity: Mechanisms, Application, Influence Factor, and Future Perspective.

Thermally processed foods are essential in the human diet, and their induced allergic reactions are also very common, seriously affecting human health. This review covers the effects of thermal processing on food allergenicity, involving boiling, water/oil bath heating, roasting, autoclaving, steaming, frying, microwave heating, ohmic heating, infrared heating, and radio frequency heating. It was found that thermal processing decreased the protein electrophoretic band intensity (except for infrared heating and radio frequency heating) responsible for destruction of linear epitopes and changed the protein structure responsible for the masking of linear/conformational epitopes or the destruction of conformational epitopes, thus decreasing food allergenicity. The outcome was related to thermal processing (e.g., temperature, time) and food (e.g., types, pH) condition. Of note, as for conventional thermal processing, it is necessary to control the generation of the advanced glycation end products in roasting/baking and frying, and the increase of structural flexibility in boiling and water/oil bath heating, autoclaving, and steaming must be controlled; otherwise, it might increase food allergenicity. As for novel thermal processing, the temperature nonuniformity of microwave and radio frequency heating, low penetration of infrared heating, and unwanted metal ion production of ohmic heating must be considered; otherwise, it might be the nonuniformity and low effect of allergenicity reduction and safety problems.

Combining radio frequency heating and alkaline treatment for enhancement of sludge disintegration and volatile fatty acids production from anaerobic fermentation

Sludge pretreatment plays a crucial role in solubilizing particulate matters to release organic matter for subsequent anaerobic fermentation (AF). This study innovatively combines radio frequency (RF) heating and alkaline treatment, and finds that the combined pretreatment achieved a sludge disintegration rate of 35.11 %, which is 15.19 % and 8.48 % higher than single RF or alkaline pretreatment. The dissociated ions from the alkali are conducive to RF action on sludge. Furthermore, the combined pretreatment significantly benefits the subsequent AF experiments, resulting in a 9-fold increase in volatile fatty acids production. Considering cost-effectiveness, the optimal operating condition is a 10-minute RF treatment at pH 10 with a total cost of 4.35 × 10-3 dollars per kg soluble chemical oxygen demand (SCOD) increased. These findings provide a foundational basis for the development of a novel technology for sludge pretreatment.

Application of radio frequency energy in processing of fruit and vegetable products.

Thermal processing is commonly employed to ensure the quality and extend the shelf-life of fruits and vegetables. Radio frequency (RF) heating has been used as a promising alternative treatment to replace conventional thermal processing methods with advantages of rapid, volumetric, and deep penetration heating characteristics. This article provides comprehensive information regarding RF heating uniformity and applications in processing of fruit and vegetable products, including disinfestation, blanching, drying, and pasteurization. The dielectric properties of fruits and vegetables and their products have also been summarized. In addition, recommendations for future research on RF heating are proposed to enhance practical applications for fruits and vegetables processing in future.

Effect of hot air-assisted radio frequency rotation heating system on improving heating uniformity of dried black fungus (Auricularia auricula)

A large-capacity radio frequency (RF) rotation heating system was employed in this study to heat dried black fungus, and hot air was used for assistance treatment. The effects of electrode gap, rotation rate and hot air on the uniformity of RF heating of dried black fungus were explored. The optimal heating process parameters were obtained, and the sterilization effect was validated. The results showed that the rotation system could significantly enhance the RF heating uniformity of black fungus (P > 0.05). The optimal heating process for heating a large-capacity (480 g) black fungus was to utilize RF heating assisted by 70 °C hot air with an electrode gap of 175 mm and a rotation rate of 60 rpm, followed by 30 min of heat preservation at 70 °C hot air with a rotation rate of 40 rpm. After the entire sterilization treatment, the heating uniformity index λ of black fungus was reduced to 0.027 ± 0.004, the total plate count decreased by 3 log CFU/g, and the moisture content dropped to below 13 %. The ideal RF heating uniformity and sterilization effect of black fungus were obtained in this study through the simultaneous use of hot air and rotation, providing a theoretical foundation for the application of RF technology in the processing of black fungus.

Determination of dielectric properties of lead-contaminated soils: Potential application to soil remediation

This research investigated the effectiveness of radio frequency (RF) heating as a treatment for lead-contaminated soil, assessing its impact through dielectric constant measurements. Using water-soluble lead (II) acetate trihydrate, the study analyzed the impact of RF heating on soil dielectric properties under various soil moisture conditions (high, medium, and low) and electric field strengths (112.5, 150, 225, and 450 kV/m). The results indicated that soil temperature increased with lead concentration, highlighting significant changes in soil thermodynamics. Under high-humidity conditions, temperature increases were more pronounced, suggesting that higher lead concentrations elevate soil temperatures. Moreover, RF heating consistently reduced the dielectric constant as lead concentration increased, which was especially evident at higher electric field strengths. The study found that the soil resistivity approached that of uncontaminated soil, particularly at 450 kV/m electric field strength, with the highest removal rate of 46.154%. This investigation provides valuable insights into the application of RF heating for soil quality improvement in lead-contaminated environments, demonstrating how dielectric properties can reflect those of uncontaminated soil.

Extended applications of the small-scale radio frequency system for improving the heating performance of multi-component rice

With the changing lifestyles and the rapid development of the prepared food industry, there are many different multi-component rice-based foods on the market today. Further, manufacturers of multi-component foods prepare different types of rice products and provide them to markets and restaurants. In this study, the multi-component rice was heated by a self-built small 50 Ω, 13.56 MHz radio frequency (RF) heating system to explore the effective scheme for improving heating uniformity. The dielectric properties (DPs) of the single-component material (cooked rice, carrot, and sausage) were first measured and the heating rates were recorded at a selected input power level of 500 W and electrode gap of 80 mm. Based on the above results and the occurrence of edge effect, three types (I, II, and III) of the multi-component test samples were designed to compare the heating performances and the quality changes after RF treatment with three different electrode gaps (70, 80, and 90 mm). Results demonstrated that the Type-I sample arrangement resulted in a relatively shorter treatment time and a lower heating uniformity index as compared to the other two sample arrangements (Types of II and III). It also resulted in a more uniform temperature distribution and better-quality retention than that was possible with the single-component treatment. Thus, the layered scheme (Type-I) based on the DPs of the material could effectively improve the RF heating uniformity of multi-component food.

Use of Neurophysiological Monitoring during MR Imaging–Guided Ablation Procedures at 1.5 T: Workflow and Safety Considerations

PurposeTo evaluate the feasibility of intraoperative neurophysiological monitoring (IONM) during magnetic resonance (MR) imaging–guided ablations and identify strategies to reduce IONM electrode radiofrequency (RF) heating during MR imaging. Materials and MethodsEx vivo experiments with a porcine tissue phantom simulating a typical high RF heating risk IONM setup during an MR imaging–guided ablation procedure on the shoulder were performed using a 1.5-T scanner. Mutual interference between MR imaging and IONM was evaluated. To assess RF heating risks, 4 pairs of IONM electrodes were inserted into the phantom at regions corresponding to the shoulders, midarm, and wrist. MR imaging of the “shoulder” was performed at 3 different specific absorption rates (SARs) with electrode wires positioned in various geometric configurations. Different combinations of electrode connections to the IONM system were investigated. Temperatures of each electrode were recorded using fiber-optic sensors. ResultsSimultaneous IONM readout and MR imaging resulted in distortion of the IONM signal, but interleaving MR imaging and IONM without moving electrodes was feasible. During MR imaging, temperature elevations greater than 60°C at the electrode insertion sites were observed. Temperature reductions were achieved by routing electrode wires along the scanner central axis, reducing the wire length within the scanner bore, or lowering the SAR of the imaging sequence. Altering the electrode connection with the IONM system did not result in consistent changes in RF heating. ConclusionsWith electrodes in the scanner bore, interleaving IONM and MR imaging is desired to avoid signal interference, and several strategies identified herein can reduce risk of electrode RF heating during MR imaging–guided ablation.

Radio Frequency Joule Heating for Healing and Reversible Adhesion Enabled by Dynamic Covalent Bonds

Herein, radio frequency (RF) Joule heating is used to trigger dynamic covalent bond exchange in a furan‐maleimide Diels–Alder polymer (DAP). Prior work shows that carbon susceptors can be incorporated into materials and undergo Joule heating when exposed to an electric field. Herein, carbon nanotubes (CNTs) are added to the DAP to make the material responsive to RF fields, and to enable selective, noncontact healing behavior of DAP after electric field exposure. After healing, mechanical testing is conducted to compare the tensile strength and toughness of the healed samples with the mechanical properties of the original, undamaged samples. A 96.2% recovery in tensile strength and an 83.2% recovery in toughness are observed. Also, RF heating of DAP/CNT enables repeated bonding and debonding of the material, allowing for adhesion and deadhesion on demand.

Helmet Radio Frequency Phased Array Applicators Enhance Thermal Magnetic Resonance of Brain Tumors.

Thermal Magnetic Resonance (ThermalMR) integrates Magnetic Resonance Imaging (MRI) diagnostics and targeted radio-frequency (RF) heating in a single theranostic device. The requirements for MRI (magnetic field) and targeted RF heating (electric field) govern the design of ThermalMR applicators. We hypothesize that helmet RF applicators (HPA) improve the efficacy of ThermalMR of brain tumors versus an annular phased RF array (APA). An HPA was designed using eight broadband self-grounded bow-tie (SGBT) antennae plus two SGBTs placed on top of the head. An APA of 10 equally spaced SGBTs was used as a reference. Electromagnetic field (EMF) simulations were performed for a test object (phantom) and a human head model. For a clinical scenario, the head model was modified with a tumor volume obtained from a patient with glioblastoma multiforme. To assess performance, we introduced multi-target evaluation (MTE) to ensure whole-brain slice accessibility. We implemented time multiplexed vector field shaping to optimize RF excitation. Our EMF and temperature simulations demonstrate that the HPA improves performance criteria critical to MRI and enhances targeted RF and temperature focusing versus the APA. Our findings are a foundation for the experimental implementation and application of a HPA en route to ThermalMR of brain tumors.