Microwave and microwave-vacuum drying as alternatives to convective drying in barley malt processing

Novel Strategies for Yuba Quality Improvement: Protein Modification Based on Physical Fields

This study investigated the effects of physical field protein modification methods on the mechanical properties, color, rehydration performance, thermal stability, and sensory quality of yuba. The results showed that all three modification methods shortened the drying time of yuba, and each method enhanced the tensile strength and thermal stability of yuba. Yuba treated with microwave-vacuum for 10 min demonstrated the best performance in terms of tensile strength, elongation, color, and overall sensory score, making it the optimal method for the physical field modification of yuba. In addition, microwave-vacuum treatment led to better rehydration performance, thermal stability, and a faster rehydration rate. Through the analysis of the microstructure of yuba as well as its protein secondary and tertiary structures, it was found that microwave-vacuum treatment can maintain the tissue network structure of yuba while promoting more heat-induced protein conformational changes, showing a greater increase in the content of β-sheets, which contribute to enhancing the tensile strength and water-holding capacity of yuba, thereby improving its product quality.

Optimization of the Vacuum Microwave Drying of Tilapia Fillets Using Response Surface Analysis

This study looked at how vacuum microwave drying (VMD) affects the quality of tilapia fillets (Oreochromis spp.). It focused on the impact of fillet thickness, microwave power, and vacuum pressure on key quality parameters, such as water activity (Aw), texture, rehydration rate, and whiteness. A series of experiments were conducted with varying fillet thickness (3-7 mm), microwave power (132-396 W), and vacuum pressure (0.03-0.07 MPa) using a Box-Behnken design to optimize drying conditions. The findings revealed that fillets with a thickness of 3 mm had the lowest Aw and the highest hardness, while 7 mm thick fillets had the best rehydration rate, elasticity, and whiteness. Additionally, increasing microwave power caused a gradual decrease in Aw and whiteness, while elasticity, hardness, and the rehydration rate initially increased and then decreased. As vacuum pressure increased, Aw decreased, and both whiteness and elasticity improved. The optimal drying conditions for tilapia fillets were identified as 7 mm thickness, 330 W microwave power, and 0.06 MPa vacuum pressure. Under these conditions, the dried fillets achieved a comprehensive quality score of 93.94. The regression model developed for optimization showed strong predictive performance, with a minimal deviation of only 1.45% from the experimental results, indicating its reliability for predicting drying effects.

Study on Influence of Microwave Electric Field Direction on Evaporation Based on Molecular Dynamics

Microwave-assisted evaporation technology is widely used today, but its molecular mechanism is not fully understood. To investigate the molecular mechanism of the influence of microwave electric field direction on water evaporation, this paper designed experiments to measure the microwave energy required to evaporate each gram of water with electric field directions parallel and perpendicular to the water surface. The temperature rise curve of the water is controlled to be consistent in both cases, and the temperature distribution of the water is made uniform by stirring. We found a stable difference in the energy absorbed by the two situations, indicating that the direction of the microwave electric field has an effect on water evaporation. In this article, the evaporation behavior of water molecules under different directional electric fields was then studied by molecular dynamics. The SPCE water molecule model, which simulates pure water systems well, was selected for this calculation. Based on the GROMOS force field, the evaporation enthalpy and surface tension of water under various conditions at constant temperature were calculated and the conclusions were analyzed. The calculated results are in agreement with the experimental results, and the influence of the evaporation enthalpy of water molecules is related to the direction of the microwave electric field.

Exploration of the impact of different drying methods on the quality of Gastrodia elata: A study based on drying kinetics and multidimensional quality evaluation

In this study, the drying kinetics and multidimensional quality of Gastrodia elata (GE) obtained through five different drying methods were analyzed. The Page model provided the best fit. Though widely used, hot-air drying (HA-D) showed mediocre performance. Due to strong heat penetration, microwave drying (MV-D) and infrared drying (IR-D) effectively reduced drying time and energy consumption. However, they experienced Maillard and caramelization reactions, resulting in notable cell structure shrinkage, severe browning, pronounced caramel taste, and poor retention of active ingredients. Conversely, freeze-drying (F-D) and vacuum drying (V-D), due to the involvement of low-temperature or vacuum environments, demonstrated optimal performance in preserving microstructure, antioxidant activity, active ingredients, and flavor. However, F-D was time-consuming (1320 min) and had an energy consumption of 2.69 times that of HA-D, limiting its large-scale application. V-D struck the best balance between energy consumption and product quality, making it a highly promising drying method for GE.

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.

Drying kinetics and energy efficiency of soot ash of smelting silicon manganese alloys under microwave heating

When smelting silicon manganese alloy in an industrial electric furnace, it will produce smoke and dust waste gas, which can be utilized again back to the furnace and improve the utilization rate of raw materials after a particular trapping device and collection treatment. However, at higher moisture levels, they are prone to explode. Effects of various initial masses, initial moisture contents, and microwave output powers on the soot ash of smelting silicon manganese alloy were studies. The findings indicate that the microwave drying rate increases with all three variables. The time for complete microwave drying is directly proportional to the sample's initial moisture content and the sample's initial mass, and the time for complete microwave drying is inversely proportional to the microwave output power. The results demonstrate that the Modified Page model can accurately describe the microwave drying process. The experimental data were fitted experimentally by drying kinetic models. Microscopic characterization of soot ash from refining silico‑manganese alloys before and after drying was carried out using FTIR and SEM. Through FTIR characterization, the peak value of the -OH absorption peak decreases upon drying, and SEM results in no agglomeration caused by microwave drying and better dispersion of the soot ash of the dried smelted silica‑manganese alloys, all of which proved that microwaves could effectively remove water. It was discovered that the diffusion coefficient increased gradually with increasing power when it was computed using Fick's second law. The diffusion coefficient increases and then decreases as the moisture content increases. The diffusion coefficient decreases as the initial mass increases. Activation energy of microwave drying of soot ash from the refining of silicomanganese alloys was calculated to be -1.4467 W/g. Its purpose is to offer a detailed guide for the industrial drying of soot ash from silicomanganese alloy refinement using microwave drying technology.

Enhanced Quick-Cooking Red Beans: An Energy-Efficient Drying Method with Hot Air and Stepwise Microwave Techniques

This research introduced an energy-efficient drying method combining hot-air drying with stepwise microwave heating for producing quick-cooking red beans. Crucial parameters such as the effective diffusivity coefficient (De), and specific energy consumption (SEC) were examined across varying conditions with the aim of optimizing the drying condition. The results showed that De and SEC varied in a range of 0.53 × 10-9-3.18 × 10-9 m2·s-1 and 16.58-68.06 MJ·(kg·h-1)-1, respectively. The findings from the response surface methodology indicated that optimal drying conditions for cooked red beans are achieved at a hot air temperature of 90 °C, a microwave power of 450 W (corresponding to an initial intensity of 2.25 W·g-1), and a rotational speed of 0.2 Hz. These conditions lead to the maximum effective diffusivity coefficient and the lowest specific energy consumption. Further investigations into step-up (150-300 W to 300-450 W) and step-down (300-450 W to 150-300 W) microwave heating modes were conducted to refine the drying process for enhanced energy efficiency. The synthetic evaluation index revealed that step-down microwave heating strategies of 450 W-to-150 W and 300 W-to-150 W, applied at a temperature of 90 °C and a rotational speed of 0.2 Hz, were notably effective. These methods successfully minimized energy use while preserving the quality attributes of the final product, which were comparable to those of traditionally cooked and freeze-dried red beans. The combined approach of hot-air drying with step-down microwave heating presents a promising, energy-saving technique for producing quick-cooking beans that retain their rehydration qualities and texture.

Drying Kinetics of Microwave-Assisted Drying of Leaching Residues from Hydrometallurgy of Zinc

In the hydrometallurgical process of zinc production, the residue from the leaching stage is an important intermediate product and is treated in a Waelz kiln to recover valuable metals. To ensure optimal results during the Waelz kiln process, it is necessary to pre-treat the residues by drying them first due to their higher water content. This work studies the residue's drying process using microwave technology. The study results indicate that microwave technology better removes the residue's oxygen functional groups and moisture. The dehydration process's effective diffusion coefficient increases as the microwave's heating power, the initial moisture content, and the initial mass increase. The Page model is appropriate for imitating the drying process, and the activation energy of the drying process for the residues is -13.11217 g/W. These results indicate that microwave technology efficiently dries the residues from the leaching stage. Furthermore, this study provides a theoretical basis and experimental data for the industrial application of microwave drying.

Effects of different drying treatments on the microstructure, free amino acids, volatile compounds and antioxidant activity of Flammulina velutipes root

Drying treatments are an effective method of preserving the beneficial properties of postharvest mushrooms. The effects of natural-air drying (ND), hot-air drying (HD), vacuum-freeze drying (FD), heat pump drying (HPD) and microwave-vacuum drying (MVD) on the microstructure, flavor- and health-related compounds of F. velutipes root were investigated. The results showed that FD had the least impact on the microstructure of F. velutipes root and its original porous fiber structure appeared complete. It also possessed the highest content of volatile compounds. MVD gave the highest contents of umami amino acids, total phenolics and total flavonoids, and its extract exhibited high antioxidant activity. In addition, different drying treatments had significant effect on the chemical components of F. velutipes root, with FD and MVD may be the potent drying strategies for preservation of flavor and nutraceuticals respectively. Therefore, our results provided essential data support for F. velutipes root processing and functional product development.

Application of microwave treatment for reduction of microbial load in jaggery cubes

In present study, fresh jaggery cubes were used and treated with microwave heating. Two treatment time has been selected to treat the jaggery such as 30 s and 45 s. Physiochemical and microbial parameters were analysed before and after treatment of microwave. Moisture content of treated jaggery sample was 3.98 ± 0.59 and 3.86 ± 0.63 for 30 s and 45 s microwave treatment respectively. Similarly, this treatment maintains the water activity at 0.6, which is considered as a safe for consumption. The content of iron retains in this microwave treatment; it doesn't affect much on the iron content present in fresh Jaggery sample. Most substantial result has been observed in case of total plate count and yeast and mold count when treated with microwave heating. In this case microwave process at 45 s was found to be the best since it reduced the total plate count (TPC) load to 13 ± 4 from 194 ± 48 cfu/g. Also, in case on yeast and mold count, 45 s microwave treatment showed reduction of load to 28 ± 7 cfu/g from 25,498 ± 2809 cfu/g. Present investigation showed that microwave treatment for 45 s was found to be the best to treat the jaggery.

Effects of drying methods on bioactive components of Ganoderma lucidum fermented whole wheat in products & in vitro digestive model

The content of bioactive components is the key to determining the quality of Ganoderma lucidum fermented whole wheat (GW) products, and drying is a necessary link in the initial processing of GW, which will affect the bioactivity and quality of GW. This paper was to assess the effect of hot air drying (AD), freeze drying (FD), vacuum drying (VD) and microwave drying (MVD) on the content of bioactive substances and the characteristics of digestion and absorption of GW. The results showed that FD, VD and AD were beneficial to the retention of unstable substances such as adenosine, polysaccharide and triterpenoid active components in GW, and their contents were 3.84-4.66 times, 2.36-2.83 times and 1.15-1.22 times of MVD, respectively. The bioactive substances in GW were released during digestion. The bioavailability of polysaccharides in the MVD group (419.91 %) was significantly higher than that in the FD, VD and AD groups (68.74 %-78.92 %), but their bioaccessibility (5.66 %) was lower than that in the FD, VD and AD groups (33.41 %-49.69 %). Principal component analysis (PCA) showed that VD is more suitable for GW drying due to the comprehensive performance of 3 aspects in terms of active substance retention, bioavailability and sensory quality.

Effect of different drying techniques on rose (Rosa rugosa cv. Plena) proteome based on label-free quantitative proteomics

To explore the molecular mechanisms of different processing technologies on rose tea (Rosa rugosa cv. Plena), we investigated the rose tea proteome (fresh rose tea [CS], vacuum freeze-drying rose tea [FD], and vacuum microwave rose tea [VD]) using label-free quantification proteomics (LFQ). A total of 2187 proteins were identified, with 1864, 1905, and 1660 proteins identified in CS, FD, and VD, respectively. Of those, 1500 proteins were quantified. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation and enrichment analysis of differential expression proteins (DEPs) in VD vs. CS, FD vs. CS, and FD vs. VD showed that these pathways were associated with energy metabolism, the metabolic breakdown of energy substances and protein biosynthesis, such as oxidative phosphorylation, citrate cycle, carbon metabolism pathways, and ribosome and protein processing in endoplasmic reticulum. FD could ensure the synthesis of protein translation and energy metabolism, thereby maintaining the high quality of rose tea.

Flavor properties of Chinese noodles processed by dielectric drying

Volatile organic compounds (VOCs) significantly impact food flavor. In this work, Electron nose (E-nose), head space solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), and head space-gas chromatography-ion mobility spectrometry (HS-GC-IMS) techniques were applied to analyze different drying effects: microwave, hot air, and radio frequency on the aroma of Chinese noodles. E-nose analysis suggests that aromatic differences are mainly from broad range-methane. HS-SPME-GC-MS and HS-GC-IMS identified 47 and 26 VOCs in the fresh and dried noodles, respectively. The VOCs in the dried noodles were mainly aldehydes, alcohols, and esters. Drying significantly reduced the types of VOCs in Chinese dried noodles. Microwave dried noodles exhibited the strongest aroma after the shortest time of treatment, suggesting microwave drying may be the best drying method for noodles. Using aromatic analysis, this paper provides useful information for understanding the flavor of flour products and offers new ideas for drying noodles.

Effect of Thermal and Non-Thermal Technologies on Kinetics and the Main Quality Parameters of Red Bell Pepper Dried with Convective and Microwave-Convective Methods

The drying process preserves the surplus of perishable food. However, to obtain a good-quality final product, different pretreatments are conducted before drying. Thus, the aim of the study was the evaluation of the effect of thermal (blanching treatments with hot water) and non-thermal technologies (pulsed electric field (PEF) and ultrasound (US)) on the kinetics of the drying process of red bell pepper. The convective and microwave-convective drying were compared based on quality parameters, such as physical (water activity, porosity, rehydration rate, and color) and chemical properties (total phenolic content, total carotenoids content, antioxidant activity, and total sugars content). The results showed that all of the investigated methods reduced drying time. However, the most effective was blanching, followed by PEF and US treatment, regardless of the drying technique. Non-thermal methods allowed for better preservation of bioactive compounds, such as vitamin C in the range of 8.2% to 22.5% or total carotenoid content in the range of 0.4% to 48%, in comparison to untreated dried material. Moreover, PEF-treated red bell peppers exhibited superior antioxidant activity (higher of about 15.2-30.8%) when compared to untreated dried samples, whereas sonication decreased the free radical scavenging potential by ca. 10%. In most cases, the pretreatment influenced the physical properties, such as porosity, color, or rehydration properties. Samples subjected to PEF and US treatment and dried by using a microwave-assisted method exhibited a significantly higher porosity of 2-4 folds in comparison to untreated material; this result was also confirmed by visual inspection of microtomography scans. Among tested methods, blanched samples had the most similar optical properties to untreated materials; however non-thermally treated bell peppers exhibited the highest saturation of the color.

Quality of Milled Rice from Large-Scale Dried Paddy Rice by Hot Air Combined with Radio Frequency Heating

A scaled-up process for paddy drying was developed using hot air (HA) combined with radio frequency (RF) heating. The study was conducted using hot air (control treatment) arranged in descending order in four temperature levels, namely 80 °C at moisture content of 25–26%, 70 °C at moisture content of 20–25%, 60 °C at moisture content of 17–20%, and 50 °C at moisture content of 13–17%, as well as with hot air combined with radio frequency (HA/RF) at different paddy temperatures (45–60 °C) by adjusting the appropriate RF energy when passing through RF heating chamber, namely HA/RF45, HA/RF50, HA/RF55, and HA/RF60. Each treatment was performed in three replicates and data were statistically analyzed in a randomized complete block design. The quality attributes of paddies affected by the drying process were assessed: fissure percentage, color, milling quality, and sensory evaluation. The drying efficiency showed that the drying time and the specific energy consumption could be decreased by up to 54.44% and 23.17% at HA/RF60 and HA/RF45, respectively. As the RF heating temperature increased, the fissure percentage of brown rice kernels at HA/RF45 and HA was not significantly impacted. Regarding color evaluation, combining RF heating and convective drying at all given conditions could be statistically applied in terms of the b*, WI, and ΔE* value. Considering the milling yield of HA as the baseline, head rice yield was maximized at HA/RF45, while bran yield reached the maximum at HA/RF60. The liking score of cooked rice after it was dried using the HA method was the highest. This study concludes that the HA/RF45 was the most appropriate drying condition, and this may provide preliminary exposure to the industrial drying of paddies.