Radio Frequency Heating Research Articles

Perspectives on Novel Technologies of Processing and Monitoring the Safety and Quality of Prepared Food Products.

With the changes of lifestyles and rapid growth of prepared food industry, prepared fried rice that meets the consumption patterns of contemporary young people has become popular in China. Although prepared fried rice is convenient and nutritious, it has the following concerns in the supply chain: (1) susceptible to contamination by microorganisms; (2) rich in starch and prone to stall; and (3) vegetables in the ingredients have the issues of water loss and discoloration, and meat substances are vulnerable to oxidation and deterioration. As different ingredients are used in prepared fried rice, their food processing and quality monitoring techniques are also different. This paper reviews the key factors that cause changes in the quality of prepared fried rice, and the advantages and limitations of technologies in the processing and monitoring processes. The processing technologies for prepared fried rice include irradiation, high-voltage electric field, microwave, radio frequency, and ohmic heating, while the quality monitoring technologies include Raman spectral imaging, near-infrared spectral imaging, and low-field nuclear magnetic resonance technology. These technologies will serve as the foundation for enhancing the quality and safety of prepared fried rice and are essential to the further development of prepared fried rice in the emerging market.

Simulated and Verification of Mass and Heat Transfer Coupled Model of Jujube Slices Dried by Hot Air Combined with Radio Frequency Heat Treatment at Different Drying Stages.

This study investigates the impact of radio frequency (RF) heat treatment on heat and mass transfer during the hot air drying of jujube slices. Experiments were conducted at different drying stages, comparing single-hot air drying with hot air combined with RF treatment. Numerical models using COMSOL Multiphysics® were developed to simulate the process, and the results were compared to validate the models. The maximum difference between the simulated value of the center temperature and the experimental value was 6.9 °C, while the minimum difference was 0.1 °C. The maximum difference in average surface temperature was 1.7 °C, with a minimum of 0.3 °C. The determination coefficient (R2) between the simulated experimental values of HA and the early (E-HA + RF), middle (M-HA + RF), and later (L-HA + RF) groups was 0.964, 0.987, 0.961, and 0.977, respectively. The study demonstrates that RF treatment reduces drying time, enhances internal temperature, promotes consistent heat and mass transfer, and accelerates moisture diffusion in jujube slices. Furthermore, the later the RF treatment is applied, the greater the increase in internal temperature and the faster the decrease in moisture content. This research elucidates the mechanism by which RF heat treatment influences heat transfer in hot air-dried jujube slices.

Trends in Food Pathogens Risk Attenuation.

Foodborne pathogens represent one of the most dangerous threats to public health along the food chain all over the world. Over time, many methods were studied for pathogen inhibition in food, such as the development of novel packaging materials with enhanced properties for microorganisms' growth inhibition (coatings, films) and the use of emerging technologies, like ultrasound, radio frequency or microwave. The aim of this study was to evaluate the current trends in the food industry for pathogenic microorganisms' inhibition and food preservation in two directions, namely technology used for food processing and novel packaging materials development. Five technologies were discussed in this study, namely high-voltage atmospheric cold plasma (HVACP), High-Pressure Processing (HPP), microwaves, radio frequency (RF) heating and ultrasound. These technologies proved to be efficient in the reduction of pathogenic microbial loads in different food products. Further, a series of studies were performed, related to novel packaging material development, by using a series of antimicrobial agents such as natural extracts, bacteriocins or antimicrobial nanoparticles. These materials proved to be efficient in the inhibition of a wide range of microorganisms, including Gram-negative and Gram-positive bacteria, fungi and yeasts.

Combination of radio frequency heating and antibacterial agents for microorganism control in the production of packaged tofu

The microorganism control in packaged tofu by radio frequency (RF) heating combined with antimicrobial agents was investigated. The inactivation of vegetative cells and spores by RF heating alone or in combination with antimicrobial agents was evaluated. Results showed that vegetative cells of typical food microorganisms, such as E.coli,S.aureus, and Bacillussubtilis, were completely inactivated by RF heating at 80 °C for 20 min, while no significant reduction in the population of spores was observed. Additionally, the growth of Bacillus spores was effectively inhibited by 0.312 mg/g of nisin. The total viable count (TVC) in RF-treated packaged tofu was below 2 log CFU/g during the storage at 4 or 37 °C for 10 days in the presence of nisin. Furthermore, the quality analysis indicated that the pH, texture, color, and volatile profile of samples were well maintained, which contributed to the favorable sensory acceptance of the consumers. These results suggested that effective microorganism control in packaged tofu was achieved by combining RF heating and nisin. The developed method was recommended to prevent spoilage of packaged tofu and extend its shelf-life.

Validation of Pasteurisation Temperatures for a Tomato-Oil Homogenate (salmorejo) Processed by Radiofrequency or Conventional Continuous Heating.

Salmorejo is a viscous homogenate based on tomato, olive oil and breadcrumbs commercialised as a "fresh-like" pasteurised-chilled purée. Due to its penetration, dielectric heating by radiofrequency (RF) might improve pasteurisation results of conventional heating (CH). The objective was to validate the pasteurisation temperature (70-100 °C, at 5 °C intervals) for salmorejo processed by RF (operating at 27.12 MHz for 9.08 s) or conventional (for 10.9 s) continuous heating. The main heat-induced changes include: orangeness, flavour homogenisation, loss of freshness, thickening, loss of vitamin C and lipid oxidation. Both CH and RF equivalent treatments allowed a strong reduction of total and sporulated mesophilic microorganisms and an adequate inhibition of the pectin methylesterase, peroxidase and, to a lesser extent, polyphenol oxidase but did not inhibit the polygalacturonase enzyme. Pasteurisation at 80 °C provided a good equilibrium in levels of microbiological and enzymatic inhibition and thermal damage to the product. Increasing this temperature does not improve enzyme inactivation levels and salmorejo may become overheated. A "fresh-like" good-quality salmorejo can be obtained using either conventional or radiofrequency pasteurisers.

Optimizing the trajectory of deep brain stimulation leads reduces RF heating during MRI at 3 T: Characteristics and clinical translation.

Radiofrequency (RF) induced tissue heating around deep brain stimulation (DBS) leads is a well-known safety risk during magnetic resonance imaging (MRI), hindering routine protocols for patients. Known factors that contribute to variations in the magnitude of RF heating across patients include the implanted lead's trajectory and its orientation with respect to the MRI electric fields. Currently, there are no consistent requirements for surgically implanting the extracranial portion of the DBS lead. Recent studies have shown that incorporating concentric loops in the extracranial trajectory of the lead can reduce RF heating, but the optimal positioning of the loop is unknown. In this study, we evaluated RF heating of 77 unique lead trajectories to determine how different characteristics of the trajectory affect RF heating during MRI at 3 T. We performed phantom experiments with commercial DBS systems from two manufacturers to determine how consistently modifying the lead trajectory mitigates RF heating. We also presented the first surgical implementation of these modified trajectories in patients. Low-heating trajectories included small concentric loops near the surgical burr hole which were readily implemented during the surgical procedure; these trajectories generated nearly a 2-fold reduction in RF heating compared to unmodified trajectories.Clinical Relevance- Surgically modifying the DBS lead trajectory can be a cost-effective strategy for reducing RF-induced heating during MRI at 3 T.

Rapid prediction of MRI-induced RF heating of active implantable medical devices using machine learning.

The interaction between an active implantable medical device and magnetic resonance imaging (MRI) radiofrequency (RF) fields can cause excessive tissue heating. Existing methods for predicting RF heating in the presence of an implant rely on either extensive phantom experiments or electromagnetic (EM) simulations with varying degrees of approximation of the MR environment, the patient, or the implant. On the contrary, fast MR thermometry techniques can provide a reliable real-time map of temperature rise in the tissue in the vicinity of conductive implants. In this proof-of-concept study, we examined whether a machine learning (ML) based model could predict the temperature increase in the tissue near the tip of an implanted lead after several minutes of RF exposure based on only a few seconds of experimentally measured temperature values. We performed phantom experiments with a commercial deep brain stimulation (DBS) system to train a fully connected feedforward neural network (NN) to predict temperature rise after ~3 minutes of scanning at a 3 T scanner using only data from the first 5 seconds. The NN effectively predicted ΔTmax-R2 = 0.99 for predictions in the test dataset. Our model also showed potential in predicting RF heating for other various scenarios, including a DBS system at a different field strength (1.5 T MRI, R2 = 0.87), different field polarization (1.2 T vertical MRI, R2 = 0.79), and an unseen implant (cardiac leads at 1.5 T MRI, R2 = 0.91). Our results indicate great potential for the application of ML in combination with fast MR thermometry techniques for rapid prediction of RF heating for implants in various MR environments.Clinical Relevance- Machine learning-based algorithms can potentially enable rapid prediction of MRI-induced RF heating in the presence of unknown AIMDs in various MR environments.

Low-field MRI's Spark on Implant Safety: A Closer Look at Radiofrequency Heating.

Advances in low-field magnetic resonance imaging (MRI) are making imaging more accessible without significant losses in image quality. In addition to being more cost-effective and easier to place without as much needed infrastructure, it has been publicized that the lower field strengths make MRI safer for patients with implants. To test this claim, we conducted a total of 368 simulations with wires of various lengths and geometries in a gel phantom during radiofrequency (RF) exposure at 23 MHz and 63.6 MHz (corresponding to MRI at 0.55 T and 1.5 T). Our results showed that heating in the gel around wire tips could be higher in certain cases at 0.55 T. To examine the impact on real patients, we simulated two models of patients with deep brain stimulation (DBS) implants of different lengths. These simulations provide quantitative evidence that low-field MRI is not always safer, and this paper serves to illustrate some of the basic principles involved in RF heating of elongated implants in MRI environments.Clinical Relevance- This paper illustrates the physical concepts of resonance and inductive coupling in RF heating during MRI scanning with implants through systematic simulations and discusses the impact of these principles in practice.

Fibrillation of whey protein isolate by radio frequency heating for process efficiency: Assembly behavior, structural characteristics, and in-vitro digestion

In this study, a novel technology involving radio frequency heating (RF) was applied to promote the production of whey protein isolate (WPI) nanofibrils. As the prolonged treatment time, gradual increases were observed in the conversion rate (>16 h with the conventional processes), fluorescence intensity, and free amino acid content of WPI. During the fibrillation process, WPI was hydrolyzed into small molecular weight peptides that self-assembled into fibrils, resulting in a significant increase in the ζ-potential and surface hydrophobicity. Conformational and structural changes that favored an increased content of β-sheets were confirmed by Fourier transform infrared and circular dichroism spectroscopy. A linear fibril structure with a proper aspect ratio (length/diameter, 35.50 ± 0.39) formed at 7 h. Moreover, the good resistance to proteolytic digestion (especially gastric stage) of certain fibrils makes them suitable for application as nutraceutical delivery vehicles. Our findings move a step forward for WPI fibrillation by RF heating.

Competing Effects of Radio Frequency Fields on Carbon Nanotube/Resin Systems: Alignment versus Heating

AbstractThis work shows that radio‐frequency (RF) fields can simultaneously align carbon nanotubes (CNTs) dispersed in a resin and induce Joule heating to cure the resin. The timescales of alignment and curing using RF heating are numerically computed and compared at different field strengths in order to determine a temperature where alignment happens before the matrix crosslinks. Composites are experimentally fabricated at the desired target temperature and are optically analyzed and quantified; the CNT network is successfully aligned in the direction of the applied electric field. This methodology can be used to create composites where the local alignment can be varied across the sample. Composites fabricated using RF fields have higher electrical conductivity in the direction of the aligned CNTs than an oven‐cured, randomly aligned sample. Also, RF‐cured nanocomposites exhibit higher tensile strength and modulus in the direction of alignment compared to an oven‐cured sample. Finally, it is further demonstrated how this methodology can be coupled with a direct ink writing additive manufacturing process to induce alignment in any desired direction, even orthogonal to the shear forces in the extrusion direction.

Technical note: System uncertainty on four- and eight-channel parallel RF transmission for safe MRI of deep brain stimulation devices.

Parallel radiofrequency transmission (pTx) remains a promising technology for addressing high-field magnetic resonance imaging (MRI) challenges, particularly regarding the safety of patients with implanted deep brain stimulation (DBS) devices. Radiofrequency (RF) shim optimization methods utilizing pTx technology have shown the potential to minimize induced RF heating effects at the electrode tips of DBS devices at 3 T. Research pTx system implementations often involve the combination of custom and commercial hardware that are integrated onto an existing MRI system. As a result, system characterization is important to ensure implant-friendly safe imaging conditions are satisfied for the operating range of the hardware. Utilizing electromagnetic and thermal simulations, the impact of system uncertainty is studied for the proposed 4- and 8-channel pTx system setupand its associated "safe mode" for DBS applications. Electromagnetic simulations indicated that instrumentation errors can affect the overall electric field strength experienced at the DBS lead tip, and a worst-case system uncertainty analysis predicted temperature elevations of +1.5°C in the 4-channel setup and +0.9°C in the 8-channel setup. In conclusion, system uncertainty can impact the precision of pTx RF inputs which in the worst-case, may lead to an unsafe imaging scenario and the proposed 8-channel setup may provide more robustness and thus, safer conditions for MRI of DBS patients.

Effects of radio frequency heating on the glass transition, protein structure, and volatile compounds profile of commercial powdered infant formula milk

Radio frequency (RF) has found its potential in ensuring the safety of packaged powdered infant formula milk (PIFM). PIFM was processed by RF at different temperature-holding time treatments (70 °C-115 min, 75 °C-50 min, 80 °C-25 min, 85 °C-10 min, and 90 °C-5 min) to obtain 5-log reduction of Cronobacter sakazakii, and its physicochemical characteristics were investigated. Various RF treatments possessed insignificant effects on color difference (ΔE < 1.5), solubility (>99%), crystallinity (∼5%), surface chemical composition (>30% fat, 15%–20% protein, and 45%–50% lactose), and microstructure of PIFM. Lower temperature-longer holding time treatment as 70 °C-115 min caused 51% reduction in water activity and 71% reduction in moisture content, thereby considerably increasing the glass transition temperature of PIFM from 60.3 °C to 78.4 °C. Protein secondary structures were preserved; however, 75 °C-50 min and 80 °C-25 min treatments significantly (P < 0.05) decreased the α-helix structure. All RF heating conditions significantly (P < 0.05) altered the concentration of volatile organic compounds in PIFM and increased the relative abundance of lipid oxidation substances such as (E)-2-heptenal, 2-heptanone, and n-nonanal. PIFM can be treated at 90 °C for 5 min for better quality and processing efficiency.

Influence of microbial cell morphology and composition on radio frequency heating of simple media at different frequencies

The effect of Listeria monocytogenes, Salmonella Typhimurium, and Saccharomyces cerevisiae on RF heating was studied in sterilized Milli-Q water and saline solution during treatments at 27.0 ± 0.6 MHz and 3.0 ± 0.02 MHz for 30 min. The presence of microorganisms caused a significant increase in temperature (maximum to 54.9 °C), with no significant decrease in cell numbers being observed for any conditions. For both media and frequencies, heating rates followed the order S. Typhimurium ≤ L. monocytogenes ≤ S. cerevisiae, except for heating at 3.0 ± 0.02 MHz in saline solution, where heating rates for S. cerevisiae and S. Typhimurium were equal. Generally, heating rates for microorganisms were significantly higher at 27.0 ± 0.6 MHz than at 3.0 ± 0.02 MHz, except for the S. cerevisiae case. Observed phenomena were probably caused by differences in the cell lipid and peptidoglycan content, with interaction effects with salt being present. This study was the first to investigate the influence of the presence of microorganisms on heating behavior of simple media. On the long term, more research on this topic could lead to finding specific RF frequencies more suitable for the heating of specific media and products for various applications.

Radiofrequency induced heating of biodegradable orthopaedic screw implants during magnetic resonance imaging.

Magnesium (Mg)-based implants have re-emerged in orthopaedic surgery as an alternative to permanent implants. Literature reveals little information on how the degradation of biodegradable implants may introduce safety implications for patient follow-up using medical imaging. Magnetic resonance imaging (MRI) benefits post-surgery monitoring of bone healing and implantation sites. Previous studies demonstrated radiofrequency (RF) heating of permanent implants caused by electromagnetic fields used in MRI. Our investigation is the first to report the effect of the degradation layer on RF-induced heating of biodegradable orthopaedic implants. WE43 orthopaedic compression screws underwent in vitro degradation. Imaging techniques were applied to assess the corrosion process and the material composition of the degraded screws. Temperature measurements were performed to quantify implant heating with respect to the degradation layer. For comparison, a commercial titanium implant screw was used. Strongest RF induced heating was observed for non-degraded WE43 screw samples. Implant heating had shown to decrease with the formation of the degradation layer. No statistical differences were observed for heating of the non-degraded WE43 material and the titanium equivalent. The highest risk of implant RF heating is most pronounced for Mg-based screws prior to degradation. Amendment to industry standards for MRI safety assessment is warranted to include biodegradable materials.

Modeling and Operation of Series-Parallel Resonant Load in Industrial RF Dielectric Heating Application

Radio Frequency (RF) based heating application is used in multiple industries like drying cross-laminated woods, food and packaging, melting silicon etc. These industrial RF heating plants operate at frequencies of 6.78 MHz, 13.56 MHz, or 27.12 MHz (ISM band). Historically, the high frequency requirement has forced the industry to rely on vacuum tube based RF generator, which are only 60% efficient. Modern semiconductors like wide bandgap (WBG) devices have achieved the high frequency operation that is required to replace the inefficient vacuum tubes. However, a comprehensive study of load network for an industrial RF heating plant has not been undertaken such that an existing plant can be retrofitted with semiconductor based turn-key solution. In this paper the authors present design equations for an industrial RF dielectric heating load structure and suggest necessary modifications required to replace vacuum tube RF generator with voltage source converter (VSC). A new figure of merit (FOM) is defined that impacts the load structure efficiency. Finally, a small-scale prototype load is manufactured as a case study. The prototype demonstrated an output power of 750 W at 6.76 MHz with an overall efficiency of 90% from DC input to RF load which can not be achieved with a vacuum tube technology.

RF heating experiment to verify the design process of graphite target at the RAON μSR facility

The purpose of the target system for the muon spin rotation, relaxation, and resonance (μSR) facility at the Rare isotope Accelerator complex for ON-line experiments (RAON) is to induce the production of a significant number of surface muons in thermally stable experiments. The manufactured target system was installed at RAON in the Sindong area near Daejeon in 2021. The design was made conservatively with a sufficient margin of safety through ANSYS calculations; however, verification experiments had to be performed on the ANSYS calculations. Because the 600-MeV proton beam has not yet been provided, an alternative way to reproduce the calculation conditions was required. The radio frequency (RF) heating method, which has not yet been applied to the target verification experiment but has several advantages, was used. It was observed that the RF heating method has promise for testing the thermal stability of the target, and whether the target system design process was performed conservatively enough was verified by comparing the RF heating experiments with the ANSYS calculations.

A new protocol for radio frequency heating of low-moisture, viscous sauces and its temperature uniformity optimisation

AbstractRadio frequency (RF) heating of agri-food, especially low moisture viscous sauces (LMVS), have obvious advantages. However, uneven heating is one main problem of RF heating technology that has to be solved. Due to the unclear heating mechanism and the difficulty to measure the three-dimensional temperature distribution in the heated object, computer-aided analysis method was adopted. Based on the RF heating numerical calculation model after experimental verification and the characteristics of polyetherimide (PEI) assisted RF heating of peanut butter (PB), this study proposed an improved method for an existing protocol. Meanwhile, parameters of the new protocol were optimised by the Multi-objective Global Optimisation (MGO) of its surrogate model. Results demonstrated that the best size of PEI block in the new protocol was Φ100 × 9.5 mm and the positional height was 12 mm. When the pasteurisation temperature Tp was set to 70 °C and the control temperature Tc was set to 75 °C, the temperature uniformity evaluation indices, Over-shoot Temperature Control Index (OTCI) and Targeted Penetration Depth (TPD), were 0.920% and 3.975 mm, respectively. Compared with 4.845% and 4.940 mm before improvement, the new protocol achieved significant optimisation and improved the temperature uniformity effectively. This also proved the feasibility of MGO method of surrogate model in relevant studies.

Thermal behavior of CMC solutions under simulation of radio frequency pasteurization

Pasteurization and enzyme-inactivation are an economical and convenient way to provide safety and shelf-life stability. However, long heating time and non-uniform temperature distribution are the main issues of traditional thermal processing for enzyme-inactivation. Because of the volumetric heating and high heating rate, radio frequency (RF) treatment is considered as one of the most promising physical enzyme-inactivating methods. A 6 kW, 27.12 MHz RF heating system was applied to explore the effect of cylindrical container dimension and solution concentration on the thermal behavior of high-viscosity liquid food. Carboxymethylcellulose (CMC) solution as a non-Newtonian fluid was selected as a model liquid food in this study. The target temperature for enzyme inactivation was 70 °C. The experimental results showed that the electrode gap, container length, and container diameter affected the heating rate and uniformity of the liquid food. Furthermore, when the concentration of CMC solution increased from 0.5% to 2.0%, the heating rate of the solution firstly increased and then decreased, while the heating uniformity index of the solution increased from 0.008 ± 0.001 to 0.056 ± 0.002. The simulation results showed that the higher electric field strength led to a higher heating rate, temperature, and velocity of natural convection of the solution at the ends of the container. Then, the recirculation zones from the ends to the center of the container were formed, which was diminished with the increasing concentration solution, resulting in the increased maximum temperature difference of solution. The results of this research may provide useful data for subsequent continuous flow studies and information on potential RF enzyme-inactivation in high-viscosity liquid foods.

Advancements in Food Processing Technologies: Enhancing Safety, Quality, and Sustainability

Food processing technologies play a vital role in ensuring the safety, quality, and sustainability of the global food supply. This research investigates recent advancements in these technologies and their impact on food safety, product quality, and sustainability. Preservation techniques such as high-pressure processing, pulsed electric field processing, and hurdle technology are shown to enhance microbial safety while preserving nutrition and sensory attributes. Advanced thermal methods like microwave processing, ohmic heating, and radio frequency heating reduce processing time, energy consumption, and maintain product quality. Non-thermal technologies such as ultraviolet light, cold plasma, and ultrasound extend shelf life without compromising nutrition and sensory properties. Innovative packaging systems contribute to freshness, prolonged shelf life, and reduced food waste. The research emphasizes sustainable practices such as energy-efficient equipment, optimized water usage, waste reduction, and eco-friendly packaging materials. Adoption of advancements in food processing technologies can improve consumer confidence, reduce waste, and create a sustainable food supply chain. This research serves as a valuable resource for industry professionals, researchers, and policymakers seeking to implement innovative food processing technologies. Key Words: cutting-edge technologies, hurdle technology, ohmic heating, cold plasma technology

Non-thermal effect of radio frequency treatments verified by the multi-scale structure and in-vitro digestibility of sweet potato starch

To verify whether there is a non-thermal effect in the radio frequency (RF) heating process, a heat block (HB) system was used to simulate the RF process for excluding the influence of thermal effect. Sweet potato starch (SNS) slurry was treated to 60 °C by RF and HB systems with different heating rate, while the heat uniformity was determined to ensure the feasibility and reliability of the method and results. The long- and/or short - range structural, molecular, and digestive characteristics of samples were investigated to elucidate the difference of the RF and HB treatments. The X-ray diffraction patterns (XRD) analysis demonstrated that crystal pattern remained A-type, but the crystallinity of treated samples was significantly reduced. Compared with HB treatment, the RF- treated starch had a more compact, or ordered structure, higher z-average radius of gyration (Rz), peak viscosity (PV) and setback (SB) based on small angle X-ray scatter (SAXS), Fourier-transform infrared spectra (FTIR), size-exclusion chromatography (SEC) and pasting properties observations, respectively. Especially, RF- treated starches with higher heating rate had lower weight-average molar mass (Mw), rapidly and slowly digestive starch content, resulting in the highest resistant starch content and polydispersity index (PDI) in comparison with other samples. The structural characteristics and digestibility of starch were significantly different between RF and HB treatments under the same conditions. This study may provide valuable insights into the thermal and non-thermal effects of RF treatment on starch structure to broaden the application of RF heating in the food processing filed.