Microwave Intensity Research Articles

Effects of microwave vacuum drying on drying characteristics, quality attributes and starch structure of germinated brown rice

Germinated brown rice (GBR) has high nutritional and health-promoting value, but the influence mechanism of microwave vacuum drying (MVD) on the quality properties of GBR is still unclear. This study investigated the effects of MVD parameters including microwave intensities (9, 12, and 15 W/g), drying temperatures (50, 60, and 70 °C), and vacuum pressures (0.03, 0.05, and 0.07 MPa) on the drying characteristics, quality attributes and starch structure of GBR. A falling-rate phase dominated the MVD process of GBR and temperature-controlled MVD significantly preserved the GABA content in GBR. MVD caused microstructural changes with rearrangement and gelatinization of starch granules in GBR. For the GBR under MVD, increasing the drying temperature resulted in a significant decrease in enthalpy (ΔH) and an increase in the degree of starch gelatinization (DSG) (P < 0.05), however, no significant effect of microwave intensity and vacuum pressure on ΔH and DSG (P > 0.05) was found. MVD reduced the relative crystallinity but hardly changed the crystal type or formed functional groups of starch molecules in GBR. Overall, temperature-controlled MVD conduced to the final quality of GBR. This study may provide a potential method to improve the quality attributes of GBR in product development applications.

The role of microwave radiation in extractive desulfurization of real diesel fuel for green environment: an experimental and computational investigation

The process of removing sulfur compounds and aromatic compounds to produce clean fuel is an important and effective contribution to the processes of mitigating and adapting to climate change. In contrast, it is necessary to find an innovative way to remove sulfur and carcinogenic aromatic compounds because clean, low-sulfur diesel is commonly used in all countries of the world at the present time. Therefore, in this work, we have studied the effect of the microwave radiation power and the irradiation time with the use of more than one type of organic solvent; methanol, acetonitrile and ethyl acetoacetate; as an extractant and solvent to feed ratio impact on the removal of sulfur and aromatic compounds of a real diesel fuel feed which has 450 ppm sulfur content and 16 wt% aromatic Content. The results showed that the best solvent used during this work was ethyl acetoacetate. According to the results, high sulfur removal (≈ 92%) was accomplished with microwave-assisted extractive desulfurization technique under the following ideal conditions: the irradiation time is 7 min, the solvent feed ratio is 3:1 and the microwave intensity is 180 W. To reveal the mechanism of microwave-assisted extractive desulfurization via different organic solvents, a theoretical study including structural examination and interaction energy analysis on the interaction between dibenzothiophene (DBT) or dimethyl dibenzothiophene (DMDBT) and the different organic solvents was also conducted.

Effective pretreatment of microwave combined with acetic acid soaking on oil absorption and quality of fried potato chips.

This study applied a combined pretreatment method involving microwave and acetic acid (AA) soaking to monitor oil absorption of fried potato chips based on texture and microstructure characteristics. Results demonstrated that medium-low microwave combined with 4 h of AA soaking significantly improved the texture profile of potato chips, and reduced oil content by approximately 53.25%. Higher microwave intensity led to greater surface roughness of samples, whereas AA soaking for 1-4 h effectively reduced surface roughness. The decrease in Fm and Nwr, along with the increase in Fwr and Wc with prolonged AA soaking time for 1-4 h indicated that medium-low microwave intensity combined with AA pretreatment enhanced hardness and brittleness of samples. Microscopic examination of cell structure revealed that this combined pretreatment facilitated pectin gelation between the cell walls of potato chips, resulting in a more intact cell structure with fewer gaps. Additionally, the color of pretreated potato chips became brighter. The combination of medium-low microwave intensity and AA soaking pretreatment resulted in a decrease in the oil content and improved the texture profile of fried potato chips. This study provides new strategies and insights for producing low-fat potato chips based on low-cost pretreatment. © 2024 Society of Chemical Industry.

Extreme ultraviolet emission spectra of a low-pressure microwave neon discharge

In this paper, in order to reveal the discharge mechanism and optimize the extreme ultraviolet (EUV) emission lines in intensity of a low-pressure microwave (MW) neon discharge, the EUV neon spectra is carefully characterized under varied MW powers and neon pressures. The corona balance is verified to be valid for the neon upper levels of the measured EUV lines, and the electron temperature T e is derived by the modified Boltzmann plot method and the line-ratio method. Both results of the methods present a decreasing trend of T e with growing neon pressure, but the values in a range of 1.87-5.77 eV deduced by the former method is in general lower than that calculated by the latter with a range of 2.23–5.58 eV in similar neon pressure range. It is also found that the increase of MW power from 90 to 135 W only leads to a slight increasing of T e . A global model is applied to estimate the electron density n e , which is found to lie in the order of magnitude of 1010 cm−3. The dependence of the plasma parameters on different discharge conditions is analysed in detail, which in turn provide a favourable basis for further optimization of the promising low-pressure MW discharge radiation source.

Numerical simulation of continuous microwave drying of rice grains

AbstractTo comprehensively understand temperature and moisture changes in a continuous microwave rice grain drying system, this study proposes a simulation strategy that facilitates the continuous movement of rice grains. The study establishes a three‐dimensional model concerning multiple physical fields, including electromagnetism, heat, and mass transfer. It examines the effects of rice grain layer thickness and microwave intensity on the moisture and temperature of rice grains. The results indicate that the drying rate is negatively correlated with material thickness but positively correlated with temperature. The optimal thickness for the rice grain layer is 8 mm. Furthermore, both the microwave drying rate and temperature increase with microwave intensity. These findings contribute to a deeper understanding of the hydrothermal change mechanisms in rice grains during microwave drying.Practical applicationsMicrowave drying, as an emergent drying technology, has garnered widespread attention for its selective heating, efficient drying, energy savings, and environmental protection. Nevertheless, enhancing uniformity during the microwave heating process constitutes an important research topic in scientific research and technological applications. Numerical simulation methods can visually analyze electric field distribution, thereby optimizing microwave heating uniformity and improving drying effects. This article aims to accurately predict the continuous microwave drying time of paddy and maximize energy usage by optimizing drying thickness and microwave power parameters establishing a mathematical model for the process. The study not only provides a solid theoretical basis for microwave dryer design but also scientifically guides the continuous microwave drying of rice and other food crops.

Impact of maltodextrin, egg white protein addition and microwave-assisted foam mat drying on drying kinetics, microstructures, physicochemical and quality attributes of jackfruit juice powder

This study aimed to analyze the effect of maltodextrin and egg white protein addition on the physicochemical, functional, microstructures, and drying characteristics of microwave-assisted foam mat-dried (MFD) jackfruit juice powders. A microwave intensity of 1 W/g was employed to obtain optimal yield and high quality of the powders. The concentration of maltodextrin influenced the drying rate of the jackfruit juice powders, with higher concentrations resulting in a faster drying rate. The data obtained from Microwave-assisted foam mat drying of the jackfruit juice powder data were best fitted by the Page and Logarithmic kinetic models. The moisture content of the jackfruit powders ranged from 1.323 ± 0.75 g/100 g (w.b.) to 1.712 ± 0.72 g/100 g (w.b.). Powders produced at higher maltodextrin/egg white protein ratios exhibited superior flowability, lower cohesiveness, smoother and smaller particle sizes, but degraded color quality. The maltodextrin concentration significantly influences the antioxidant properties of the powders. The water sorption of jackfruit juice powder was determined, and the findings showed a good fit with the Guggenheim–Anderson–de Boer (GAB) model.

Microwave and ultrasound-assisted natural deep eutectic solvents-based extraction of pectin from onion peel wastes

ABSTRACT Pectin was extracted from onion peels using microwave and ultrasound-assisted natural deep eutectic solvents (NADES) and compared with conventional acid-extracted pectin. The primary screening trials indicated that the suitable combination of hydrogen bond acceptor and donor was choline chloride and tartaric acid, respectively. The Box-Behnken design was further used to optimize processing conditions like microwave intensity (26.903 W/g), microwave processing duration (2.99 min), and sonication duration (10.18 min) for maximizing the pectin yield from onion peel powder. The moisture, ash, and equivalent weight of extracted pectin were in the range specified by the International Pectin Producers Association. The higher anhydrouronic acid content of the NADES-extracted pectin indicated the higher purity of pectin compared to the conventional acid-extracted pectin. The NADES-based extraction was found to be a promising system for extracting pectin with a higher degree of esterification from onion peels.

Structural Characterization and Antioxidant Activity of β-Glucans from Highland Barley Obtained with Ultrasonic-Microwave-Assisted Extraction.

In order to efficiently extract β-glucan from highland barley (HBG) and study its structural characterization and antioxidant activity, ultrasonic-microwave-assisted extraction (UME) was optimized by the response surface method (RSM). Under the optimal extraction conditions of 25.05 mL/g liquid-solid ratio, 20 min ultrasonic time, and 480 W microwave intensity, the DPPH radical scavenging activity of HBG reached 25.67%. Two polysaccharide fractions were purified from HBG, namely HBG-1 and HBG-2. Structural characterization indicated that HBG-1 and HBG-2 had similar functional groups, glycosidic linkages, and linear and complex chain conformation. HBG-1 was mainly composed of glucose (98.97%), while HBG-2 primarily consisted of arabinose (38.23%), galactose (22.01%), and xylose (31.60%). The molecular weight of HBG-1 was much smaller than that of HBG-2. Both HBG-1 and HBG-2 exhibited concentration-dependent antioxidant activity, and HBG-1 was more active. This study provided insights into the efficient extraction of HBG and further investigated the structure and antioxidant activities of purified components HBG-1 and HBG-2. Meanwhile, the results of this study imply that HBG has the potential to be an antioxidant in foods and cosmetics.

Sustainable Approach for Utilization of Mango Peel Wastes for Pectin Extraction by Natural Deep Eutectic Solvents

Sequential ultrasound‐ and microwave‐assisted natural deep eutectic solvents (NADES) were used for the extraction of pectin from mango peels in this study. The two different NADES composed of proline: malonic acid (Pro: MA) and choline chloride: tartaric acid (ChCl: TA) which resulted in higher pectin yield were selected for further optimization studies. The processing conditions such as sonication duration, microwave intensity, microwave processing duration, and liquid–solid ratio were optimized using Box–Behnken design. The optimized conditions are sonication duration (7.5 min), microwave intensity (40 W/g), microwave processing duration (5 min), and liquid–solid ratio (65%). The physicochemical and technofunctional properties of pectin extracted using NADES were compared with conventional acid–extracted pectin. The moisture and ash content of NADES‐extracted pectin were within the specified limit provided by the International Pectin Producers Association. The NADES‐based extracted pectin contains galacturonic acid content higher than 65%, as mentioned by the Joint FAO/WHO Expert Committee on Food Additives and the European Commission. The higher anhydrouronic acid content of pectin (88.8 ± 0.21%–90.82 ± 0.11%) represents the superior purity of pectin. The higher degree of esterification (&gt; 50%) indicates the extracted pectin is a high ester pectin. The similarity of FT‐IR spectra at 800–1300 cm−1 with the “fingerprint zone” of carbohydrates indicates that extracted pectin is functional pectin. The results showed that ultrasound‐ and microwave‐assisted NADES are efficient systems for extracting pectin with a high degree of esterification from mango peels.

Frequency, Intensity, and Phase Synchronous Imaging of Microwave With Nitrogen-Vacancy Center Microscopy

Frequency, Intensity, and Phase Synchronous Imaging of Microwave With Nitrogen-Vacancy Center Microscopy

Influence of Heating Intensity and Drying Time of Oven and Microwave on the Moisture and Water Activity of the Gynura procumbens Leaves

Influence of Heating Intensity and Drying Time of Oven and Microwave on the Moisture and Water Activity of the Gynura procumbens Leaves

Microwave radiation induces modifications in the protein fractions of tef flours and modulates their derived techno-functional properties

The impact of microwave (MW) treatments on the structure, solubility, and techno-functional properties of the proteins in starchy matrices is still poorly understood. This study aimed to investigate the effects of MW intensity by applying 1, 2, and 6 min of radiation on two tef flour varieties moistened at 15 % and 25 %. The fractionation method recovered ∼83 % of the total protein content in untreated flours. The interaction between treatment time and moisture content (MC) significantly influenced the extraction of protein fractions. Samples treated at 25 %MC showed significant reductions in albumins (up to −74 %), globulins (up to −79 %), and prolamins (up to −32 %). The SDS-extractable proteins of both tef flours presented similar molecular weights (12–100 kDa). SDS-PAGE analysis revealed decreased band intensity in MW-treated samples compared to untreated flours, and confocal analysis showed changes in the native state of proteins in treated samples. Shorter treatments at low MC significantly improved the emulsifying stability of tef flours, particularly in brown tef flour, with an enhancement of up to 203 %. The hydration properties significantly increased in flours treated at 25 %MC for 6 min. Pearson correlation analysis demonstrated the influence of treatment time and MC on protein recovery and functional properties of tef flours.

Effect of microwave drying on the brittleness quality of pork chip snacks: Perspectives on drying kinetics and microstructural traits

Ready-to-eat pork-based snacks have gained widespread popularity among consumers. The aim of this study was to investigate the brittleness quality of pork chip snacks (PCS) produced by microwave drying (MD) from the perspective of drying kinetics and microstructural traits. Changing microwave intensity and slice thickness significantly affected the colour and texture quality of the final PCS. The MD process of PCS presented a long heating-up phase and a short hindered drying phase, and the model of Midilli et al. described the drying kinetics well. The hindered drying phase dominated the ripening process and the formation of brittleness quality of PCS, and the temperature above 157.3 °C may cause an undesirable colour appearance. The microstructural characteristics showed that the formation of many large pores in PCS promoted the brittleness quality, while excessive temperature caused the tissue to melt with fewer pores to reduce brittleness. Overall, for fresh pork slices, it is recommended to produce PCS with a thickness of 3.5 mm at 4 W/g for 22 min to achieve a desirable brittleness quality. This study may provide a reference for the production of meat snacks such as PCS.

Microwave target location method based on thediamond NV color center.

We propose a method for microwave target source localization based on the diamond nitrogen vacancy color center. We use coherent population oscillation effect and modulation and demodulation techniques to achieve the detection of microwave intensity of microwave target sources, with a minimum detection intensity of 0.59µW. Positioning of the microwave source was achieved within 50×100c m 2 distance from the system 1m away using the cubic spline interpolation algorithm and minimum mean squared error. The maximum positioning error was 3.5cm. This method provides a new, to the best of our knowledge, idea for the passive localization of microwave targets.

Tyrosinase inhibitory activity of Sargassum fusiforme and characterisation of bioactive compounds.

Sargassum fusiforme (Harvey) Setchell, also known as Tot (in Korean) and Hijiki (in Japanese), is widely consumed in Korea, Japan, and China due to its health promoting properties. However, the bioactive component behind the biological activity is still unknown. We aimed to optimise the extraction conditions for achieving maximum tyrosinase inhibition activity by using two sophisticated statistical tools, that is, response surface methodology (RSM) and artificial neural network (ANN). Moreover, high-resolution mass spectrometry (HRMS) was used to tentatively identify the components, which are then further studied for molecular docking study using 2Y9X protein. RSM central composite design was used to conduct extraction using microwave equipment, which was then compared to ANN. Electrospray ionisation tandem mass spectrometry (ESI-MS/MS) was used to tentatively identify bioactive components, which were then docked to the 2Y9X protein using AutoDock Vina and MolDock software. Maximum tyrosinase inhibition activity of 79.530% was achieved under optimised conditions of time: 3.27 min, temperature: 128.885°C, ethanol concentration: 42.13%, and microwave intensity: 577.84 W. Furthermore, 48 bioactive compounds were tentatively identified in optimised Sargassumfusiforme (OSF) extract, and among them, seven phenolics, five flavonoids, five lignans, six terpenes, and five sulfolipids and phospholipids were putatively reported for the first time in Sargassum fusiforme. Among 48 bioactive components, trifuhalol-A, diphlorethohydroxycarmalol, glycyrrhizin, and arctigenin exhibited higher binding energies for 2Y9X. Taken together, these findings suggest that OSF extract can be used as an effective skin-whitening source on a commercial level and could be used in topical formulations by replacing conventional drugs.

Experimental validation of the intensity refractometry principle for density measurements at the edge of a tokamak

Experimental validation is presented for a new type of microwave diagnostic, first introduced in the theoretical study in M. Usoltceva et al., Rev. Sci. Instrum. 93, 013,502 (2022). A new term is adopted for this technique to highlight its difference from interferometry: intensity refractometry. The diagnostic allows measuring electron density, and in this work, it is applied at the edge of a tokamak. The implementation of this technique at ASDEX Upgrade, called Microwave Intensity refractometer in the Limiter Shadow (MILS), provides the first experimental proof of the diagnostic concept. Densities predicted by MILS are compared to several other diagnostics. The agreement and discrepancy in various radial regions of the density profile are analyzed and possible reasons are discussed. A wide density coverage is shown in the example discharges with densities from 2 × 1017 m−3 to 2 × 1019 m−3 at the limiter position. In these experiments, the radial location of the measurements varied from 5 cm in front of the limiter (up to 1 cm inside the separatrix was measured) to 3 cm in the limiter shadow. Experimental challenges of MILS operation and data processing are presented.

Ultrasound-guided microwave, radiofrequency, and high intensity focused ultrasound (HIFU) ablation in treating uterine leiomyoma: A systemic review and meta-analysis of retrospective studies

ABSTRACT To retrospectively evaluate the efficacy and safety of ultrasound-guided microwave (MWA), radiofrequency (RF), and high-intensity focused ultrasound (HIFU) ablation in the treatment of uterine leiomyoma and to provide a suggestion for the selection of clinical treatment of uterine leiomyoma. The retrospective cohort studies on the efficacy of high-intensity focused ultrasound in treating uterine leiomyoma was collected through a literature search in Pubmed, Embase, Cochrane library, Scopus, and Web of Science, and selected according to the specified inclusion criteria and exclusion criteria. Evaluate the study quality, extract relevant data, and RevMan 5.4.1 was used to conduct this meta-analysis. Compared with HIFU therapy, the complete or partial ablation rate and recurrence rate of uterine leiomyoma treated with RFA/MWA were statistically different (P < 0.05). Compared with RF, the overall efficacy of HIFU in treating uterine leiomyoma was not as good as that of RF. There was no significant difference between the RFA therapy and the MWA. HIFU still has mild and short-term complications, such as abdominal pain, bloody vaginal discharge, sacral pain, and fever. Although myomectomy is usually the first choice for uterine preservation, RFA/MWA and HIFU have also been shown to relieve clinical symptoms significantly, shorten treatment time, reduce complications, and improve prognosis.

Microwave Passive Direction-Finding Method Based on NV Color Center in Diamond

In this study, we established a passive direction-finding scheme based on microwave power measurement: Microwave intensity was detected using microwave-frequency proportion integration differentiation control and coherent population oscillation effect converting the change in microwave resonance peak intensity into a shift of the microwave frequency spectrum, for which the minimum microwave intensity resolution was −20 dBm. The direction angle of the microwave source was calculated using the weighted global least squares method of microwave field distribution. This lay in the 12~26 dBm microwave emission intensity range, and the measurement position was in the range of (−15°~15°). The average angle error of the angle measurement was 0.24°, and the maximum angle error was 0.48°. In this study, we established a microwave passive direction-finding scheme based on quantum precision sensing, which measures the microwave frequency, intensity, and angle in a small space and has a simple system structure, small equipment size, and low system power consumption. In this study, we provide a basis for the future application of quantum sensors in microwave direction measurements.

Spontaneous mode locking of a multimode semiconductor laser under continuous wave operation

Self-starting mode-locking is observed in a laser based on a compact III-V diode-pumped quantum-well surface-emitting semiconductor laser technology with a saturable-absorber-free but dispersive cavity. Continuous wave generation of picosecond pulses at a rate of 100 GHz is demonstrated by recording microwave intensity noises, beat frequency, time-resolved optical spectra, and intensity autocorrelation. Coherence of the pulse train is obtained through the frequency noise measurement of the demodulated beat note, demonstrating a timing jitter as low as 110 fs, near the quantum limit. Using a theoretical model based on a generalized Haus master equation, we demonstrate the existence of this mode locked state without the need for saturable absorption. The fundamental physical mechanism is the interplay between self-phase modulation and anomalous dispersion like in cavity soliton together with light–matter interaction-induced time symmetry breaking.

Exclusive Effect in Rydberg Atom-Based Multi-Band Microwave Communication

We have demonstrated a Rydberg atom-based two-band communication with the optically excited Rydberg state coupled to another pair of Rydberg states by two microwave fields, respectively. The initial Rydberg state is excited by a three-color electromagnetically-induced absorption in rubidium vapor cell via cascading transitions, with all of them located in infrared bands: a 780 nm laser servers as a probe to monitor the optical transmittancy via transition 5S1/2→5P3/2, 776 nm and 1260 nm lasers are used to couple the states 5P3/2 and 5D5/2 and states 5D5/2 and 44F7/2. Experimentally, we show that two channel communications carried on the two microwave transitions influence each other irreconcilably, so that they cannot work at their most sensitive microwave-optical conversion points simultaneously. For a remarkable communication quality for both channels, the two microwave fields both have to make concessions to reach a common microwave-optical gain. The optimized balance for the two microwave intensities locates at EMW1=6.5 mV/cm and EMW2=5.5 mV/cm in our case. This mutual exclusive influence is theoretically well-explained by an optical Bloch equation considering all optical and microwave field interactions with atoms.