Microwave Vacuum Drying Research Articles

Ultrasound-assisted microwave vacuum drying enhances flavor release during stewing of dried shiitake mushrooms

The introduction of ultrasonic energy into microwave vacuum drying (MVD) enhances drying efficiency and product quality. To investigate the effect of ultrasonically coupled microwave vacuum (USMVD) drying on the flavor release of shiitake mushrooms, differences in the pore structure of dried mushrooms were analyzed in relation to the flavor of mushroom soup. The results showed that ultrasound mainly changed the pore structure of shiitake mushrooms in the range of 5000–50,000 nm, and the total pore volume of shiitake mushrooms was the largest when the ultrasound amplitude was 70 %. In flavor analysis, 9 volatiles and 7 non-volatiles significantly contributed to flavor differences in shiitake mushroom soup, characterized by increased aroma, umami, and saltiness, along with decreased sourness and astringency. This study offers valuable insights for future research on high-quality drying and processing of edible mushrooms.

Effects of Drying Treatments on the Physicochemical Characteristics and Antioxidant Properties of the Edible Wild Mushroom Cyttaria espinosae Lloyd (Digüeñe Mushroom).

The wild mushroom Cyttaria espinosae, also known as digüeñe, is a parasitic ascomycete of Nothofagus trees endemic to southern Chile. This species of wild mushroom is of great nutritional importance, especially for the Mapuche indigenous communities, and is highly sought after. Edible wild mushrooms, rich in bioactive compounds, are a potential source of health-promoting components. In the case of C. espinosae, research on its bioactive compounds is still lacking as is research, on the effect of preservation treatments on these compounds due to its perishability. This study evaluates the effects of three drying treatments; freeze-drying, hot-air drying, and microwave-vacuum drying. The rehydration capacity, color, and microstructural properties of dried mushrooms were evaluated using SEM, while, total phenolic content, antioxidant activity determined by DPPH and ORAC assays, and ergothioneine levels were investigated in both fresh and dried extracts of C. espinosae. The results showed that freeze-drying and microwave-vacuum drying are recommended treatments for the digüeñe mushroom due to superior outcomes in rehydration rate, color, and structural properties observed through SEM images. Total phenolic content and antioxidant activity were higher in mushroom extracts dried by microwave-vacuum compared to the other drying treatments.

Optimization of Phenolic Content Extraction and Effects of Drying Treatments on Physicochemical Characteristics and Antioxidant Properties of Edible Mushroom Pleurotus ostreatus (Jacq.) P. Kumm (Oyster Mushroom).

Edible mushrooms have been part of the human diet for centuries. Traditionally, they have been used for culinary and medicinal purposes due to their chemical composition and nutritional value, including their high antioxidant activity attributed to key metabolites such as phenolic compounds and ergothioneine. P. ostreatus mushrooms, known for their potent antioxidant activity, are prone to spoilage shortly after harvest, making preservation methods necessary. Various drying methods were evaluated to determine their effects on physicochemical characteristics, antioxidant properties, and ergothioneine content. Mushrooms were subjected to freeze-drying (FD), hot-air-drying (HAD), and microwave-vacuum-drying (MVD). The rehydration rate, color, and microstructural characteristics of extracts from fresh and dried P. ostreatus mushrooms were evaluated. Additionally, the total soluble phenolic content and antioxidant activity were assessed using DPPH and ORAC assays, along with the determination of ergothioneine content. FD and HAD at 40 °C showed the best results regarding the physicochemical characteristics. In terms of total soluble phenolic content, antioxidant activity, and ergothioneine content, the mushrooms dried using HAD at 40 °C showed the best retention of bioactive compounds. Among the evaluated methods, HAD at 40 °C proved to be a suitable alternative for processing P. ostreatus.

Evaluation of Drying Characteristics and Quality Attributes for Microwave Vacuum Drying of Pork Skin Crisps.

As an important by-product of pork, pork skin can be processed into meat-based leisure food products to improve its utilization. In this study, microwave vacuum drying (MVD) technology was used to investigate the effects of microwave powers (600, 700, and 800 W) and processing duration on the drying characteristics and quality attributes of pork skin crisps (PSC). Five classical drying models were used to non-linearly fit the experimental data, and the Midilli et al. model was suitable for characterizing the MVD process of PSC. Before reaching a constant rate of drying, increasing microwave power and time can improve the brittleness and expansion ratio of PSC. In the constant rate drying stage, most of the free water in PSC was removed, showing the best brittleness and a stable expansion ratio. High power and long processing time can lead to serious lipid oxidation and change the flavor of PSC. Overall, the desired quality of PSC is recommended as 700 W for 6 min. This study can provide a reference for MVD application of meat-based by-product leisure foods.

A comparative evaluation of physical characteristics, bioactive compounds, and antioxidant capacity of Rhodomyrtus tomentosa berry by different drying methods

The Rhodomyrtus tomentosa berry (RTB) has attracted the attention of researchers for its medicinal and nutritional characteristics. However, there is limited research on the influence of different drying methods on RTB quality. The objective of this work was to evaluate the effect of vacuum microwave drying (VMD), heat pump drying (HPD), and sun drying (SD) on the quality characteristics, microstructure, and antioxidant capacity of RTB. Results indicated that compared with HPD and SD, VMD enhanced the quality of RTB and could complete the drying process in a shorter time (3.6 hrs). In addition, VMD was able to retain a higher level of bioactive compounds and antioxidant capacity with an improved rehydration ratio. The microscopic images showed that the VMD had an obvious porous structure, facilitating the water evaporation. This suggested that VMD is an efficient drying technology for producing high-quality dried products.

Quality variation analysis and rehydration kinetics modeling of yuba subjecting to three different drying process

This study investigated the effects of hot air drying (HAD), microwave vacuum drying (MVD), and vacuum frying drying (VFD) on the quality of yuba and utilized mathematical models (Peleg model, Weibull equation, first-order kinetic model, and exponential association model) to explore the rehydration kinetics of yuba. The results indicated that, compared to HAD, MVD significantly increased yuba's L* value and sensory score, while VFD notably reduced the cooking loss rate and enhanced moisture retention. Significant changes were observed in the texture of yuba before and after cooking, with distinct differences noted under microscopic observation, and a pronounced change in protein secondary structure. The Peleg model can effectively fit the rehydration processes of HAD and VFD yuba, while the first-order kinetic model can effectively fit the rehydration processes of MVD yuba. This study provides a valuable reference for yuba's drying method and rehydration Kinetics model.

Optimization of Variable-Temperature Pressure-Difference Puffing Drying Process for Persimmon Chips Using Response Surface Methodology.

This study focused on persimmons and applied variable-temperature pressure-differential puffing drying to produce persimmon chips. The effects of puffing pressure, holding time, drying temperature, and duration on moisture content, crispness, and sensory scores were examined. The optimal parameters determined via response surface methodology were a pressure differential of 0.46 MPa, holding time of 10 min, drying temperature of 94 °C, and drying time of 92 min, achieving a moisture content of 3.63%, crispness of 362.83 g, and sensory score of 90.8. Microstructural and porosity analysis showed that this method predominantly produced chips with large pores and enhanced pore volume (0.2949 cm3/g), porosity (30.16%), and average pore diameter (194.0 nm). Compared to microwave drying, vacuum microwave drying, and vacuum frying, the pore volume of persimmon chips processed using pressure-differential puffing drying increased by 57.7% to 237.8%, the porosity improved by 57.2% to 237.8%, and the average pore diameter grew by 82.2% to 660.8%. Notably, the differences were most pronounced when compared to vacuum frying, with increases of 237.8%, 237.8%, and 660.8%, respectively. These results indicate that pressure-differential puffing drying is superior in creating loose structures and achieving high-quality persimmon chips, making it the preferred processing method.

Microwave-vacuum drying behavior of rosehips: Experimental investigation and mathematical modeling

In this study, the microwave-vacuum drying of rosehips (Rosa canina) was investigated and the effect of different drying conditions during the microwave vacuum drying process on the drying kinetics of rosehips was determined. For this purpose, microwave vacuum drying experiments were carried out until a moisture content less than 10 % by weight was attained at three power (50, 100, and 150 W) and three pressure (40, 75, and 110 mBar (abs)) levels. The drying times ranged from 75 to 195 min depending on the power level and vacuum degree applied. Seven different mathematical models, which are most commonly used in the literature, were fitted to the experimental data, and among these models, the most suitable model was selected by considering the statistical criteria of the highest regression coefficient (R2), the lowest chi-square (χ2), total squared error (SSE) and root mean square error (RMSE). The drying rate (DR) increased with increasing microwave power levels under all pressure levels. The Midilli model was proposed as the best-fit model for predicting the drying behavior of rosehip plants under all drying process conditions. The effective moisture diffusion (Deff) of rosehips under different drying conditions during the MVD process ranged from 5.81⨮10−8-17.32⨮10−8 m2/s and increased with the increasing microwave power at constant pressure.

Different Pretreatment Methods to Strengthen the Microwave Vacuum Drying of Honeysuckle: Effects on the Moisture Migration and Physicochemical Quality.

In this study, we analyzed the effects of three pretreatment methods-microwave, steam, and blanching-on the quality of Honeysuckle to determine the optimal pretreatment method; we then investigated the influence of different drying temperatures, vacuum levels, and rotation speeds on the drying characteristics, color, and active ingredient content of the Honeysuckle that was pretreated by the optimal pretreatment method during rotary microwave vacuum drying. The results indicated that a microwave pretreatment for 75 s was the optimal pretreatment method, which enhanced the retention of active ingredients and effectively improved the browning of the material. During the process of rotary microwave vacuum drying, as the temperature increased, the vacuum level rose, and the rotation speed increased, the drying rate gradually increased. However, excessively high vacuum levels and rapid rotation speeds could actually decrease the drying rate. In addition, the total phenols, total flavonoids, antioxidant activity, and various active ingredients of Honeysuckle dried by rotary microwave vacuum were effectively preserved. Furthermore, its rehydration properties and color were significantly superior to those dried through sun drying. The TIOPSIS method analysis showed that the optimal process parameters were a temperature of 50 °C, a vacuum level of -0.070 MPa, and a rotation speed of 35 Hz, which exhibited the highest relative closeness (0.76). The comprehensive analysis indicated that microwave pretreatment followed by rotary microwave vacuum drying was a promising drying method with potential applications in the dehydration of agricultural products and medicinal plants.

Effect of Microwave–Vacuum Drying and Pea Protein Fortification on Pasta Characteristics

The widespread popularity of pasta has driven innovations in formulations and production technologies to enhance its versatility. Techniques such as alternative drying methods and fortification of wheat pasta seek to improve the nutritional value and functional properties of pasta products, thereby increasing their attractiveness to consumers. This study aimed to evaluate the effects of microwave–vacuum drying versus conventional drying on the characteristics of durum wheat semolina pasta, including moisture content, water activity, microstructure, colour, texture, weight gain factor, and cooking loss. Three types of pea protein concentrates (80, 84, and 88% dry matter) were used at levels of 3, 6, and 9% (g/100 g flour). Results indicated that microwave–vacuum drying had a significant impact on the physical properties and cooking quality of pasta. Microwave–vacuum drying caused material puffing, resulting in microstructure with high open porosity (64.1%) and minimal closed porosity (0.1%). This has likely contributed to the short rehydration time (2 min in boiling water) of produced pasta, effectively transforming it into an instant food product. All pasta samples had low water content (<9%) and water activity (<0.4), which ensure food safety. The microwave–vacuum-dried pasta weight gain factor (2.2) was lower than in the conventionally dried pasta (2.8). The firmness of microwave–vacuum-dried pasta was significantly higher (135 g) than that of conventional pasta (16 g). Fortification with pea protein enhanced porosity but did not affect pasta’s culinary parameters, such as weight gain or cooking loss, although it resulted in darker pasta (p = 0.001), especially notable with a 9% pea protein addition.

A Comparison of the Impacts of Different Drying Methods on the Volatile Organic Compounds in Ginseng.

Ginseng (Panax ginseng C. A. Meyer) is a valuable plant resource which has been used for centuries as both food and traditional Chinese medicine. It is popular in health research and markets globally. Fresh ginseng has a high moisture content and is prone to mold and rot, reducing its nutritional value without proper preservation. Drying treatments are effective for maintaining the beneficial properties of ginseng post-harvest. In this study, we investigated the effects of natural air drying (ND), hot-air drying (HAD), vacuum drying (VD), microwave vacuum drying (MVD), and vacuum freeze drying (VFD) on volatile organic compounds (VOCs) in ginseng. The results showed that the MVD time was the shortest, followed by the VFD, VD, and HAD times, whereas the ND time was the longest, but the VFD is the most beneficial to the appearance and color retention of ginseng. A total of 72 VOCs were obtained and 68 VOCs were identified using the five drying methods based on gas chromatography-ion mobility spectrometry (GC-IMS) technology, including 23 aldehydes, 19 alkenes, 10 alcohols, 10 ketones, 4 esters, 1 furan, and 1 pyrazine, and the ND method was the best for retaining VOCs. GC-IMS fingerprints, principal component analysis (PCA), Euclidean distance analysis, partial least squares discriminant analysis (PLS-DA), and cluster analysis (CA) can distinguish ginseng from different drying methods. A total of 29 VOCs can be used as the main characteristic markers of different drying methods in ginseng. Overall, our findings provide scientific theoretical guidance for optimizing ginseng's drying methods, aromatic health effects, and flavor quality research.

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.

Shaping the Physicochemical and Health-Promoting Properties of Carrot Snacks Produced by Microwave-Vacuum Drying with Preliminary Thermal and Enriching Treatment.

This study analyzed the effects of thermal pre-treatments such as convective drying (P-CD), water (BL_W), and microwave blanching (M_BL) and osmotic enrichment pre-treatments with juices from pomegranate (PG), chokeberry (CH), and sea buckthorn (SB) on microwave-vacuum-dried (MVD) carrot properties. Convective drying (CD) and freeze-drying (FD) were used as a comparative method. The dry matter content and water activity of MVD carrots were varied, but in many cases, the values were comparable to those of FD-dried carrots. Pre-enrichment in CH juice significantly reduced the values of the color parameters L*, a*, and b*, regardless of the drying method. The smallest changes were observed in microwave pre-blanching (M_BL). The lowest loss in carotenoid content was observed in CD-dried carrots (14-34 mg/100 g d.m.). Blanching and enrichment in SB juice allowed significant retention of these compounds. As a result of drying carrots, the total phenolic content (TPC) increased. Compared to the raw material, the TPC content in dried carrots increased 3-9 times. Drying using the FD and MVD methods gave a similar effect of increasing the TPC content, including a greater effect after enrichment in CH juice. The highest average antioxidant activity against the DPPH• and ABTS•+ radicals was recorded for FD-dried carrots (6.9 and 30.0 mg Trolox/g d.m.). SB juice contributed to a significant increase in the total vitamin C content, even by 89.1%, compared to raw carrots. Applying osmotic pre-enrichment in PG juice increased the sugar content in dried FD and CD samples by 37.4-49.9%, and in MVD by 21-59%.

Social life cycle sustainability assessment of dried tomato products based on material and process selection through multi-criteria decision making.

Tomatoes are a significant product of the Mediterranean region and a crucial component of the Mediterranean diet. The formulation of dried tomato products enriched with proteins and bioactive compounds could be a strategic approach to promote adherence to the Mediterranean diet. Six different novel tomato products were analyzed using different protein enrichment sources (pea proteins and leaf proteins) and drying technologies (hot-air dryer, microwave vacuum dryer, and conventional dryer). The novelty of this approach lies in combining product-specific criteria with global societal factors across their life cycles. Using 21 criteria and an analytic hierarchy process (AHP) survey of experts, the social sustainability score for each product was determined through a multi-criteria assessment. The tomato product's life cycles have minimal regional impacts on unemployment, access to drinking water, sanitation, or excessive working hours. However, they affect discrimination, migrant labor, children's education, and access to hospital beds significantly. The study identified nutritional quality as the top criterion, with the most sustainable design being a tomato bar enriched with pea protein and processed using microwave vacuum drying. The study revealed that integrating sensory and nutrient compounds into social sustainability assessments improves food sustainability and provides a practical roadmap for social life cycle assessments of food products. It emphasized the importance of considering global social issues when reformulating Mediterranean products to ensure long-term adherence to the Mediterranean diet. Incorporating social factors into sustainability scores can also enhance the effectiveness of product information for conscious customers. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Enhancing Okra Drying Quality and Efficiency Through Combined Freeze and Pulsed Spouted Microwave Vacuum Drying

Enhancing Okra Drying Quality and Efficiency Through Combined Freeze and Pulsed Spouted Microwave Vacuum Drying

Microwave vacuum drying of small round logs of plantation-grown species for the production of handicrafts

Microwave vacuum drying of small round logs of plantation-grown species for the production of handicrafts

Effects of Different Drying Methods on Drying Characteristics and Quality of Small White Apricot (Prunus armeniaca L.)

This study examined the effects of hot air drying (HAD), infrared radiation drying (IRD), microwave vacuum drying (MVD), freeze drying (FD), and freeze drying combined with microwave vacuum drying (FD-MVD) on the drying kinetics, color, rehydration ratio, titratable acidity, and vitamin C content of small white apricots (Prunus armeniaca L.). Results showed drying times of 12.5 h (IRD), 14.1 h (FD), 16 h (HAD), 0.53 h (MVD), and 6.15 h (FD-MVD). FD-MVD significantly outperformed MVD, HAD, and IRD in color, vitamin C, titratable acidity, and rehydration, though was slightly inferior to FD. Microstructural analysis revealed that FD-MVD preserved the most uniform pore structure, better maintaining apricots’ original appearance. In contrast, IRD and HAD caused severe surface shriveling, compromising quality. In conclusion, FD-MVD emerges as a promising drying method to enhance apricot quality and market competitiveness in food processing.

Quality Evaluation and Heat and Mass Transfer Mechanism of Microwave Vacuum Drying of Astragalus Roots.

In this research, the objective was to optimize the drying process of Astragalus by investigating the effects of microwave vacuum drying parameters, including temperature (30, 35, 40, 45, and 50 °C) and slice thickness (2, 3, 4, 5, and 6 mm). In addition, utilizing COMSOL 6.0 finite element analysis software, we delved into the distribution of heat and moisture during the drying process. The results revealed that drying temperature played a significantly greater role than slice thickness in determining the drying dynamics. The thermal and mass transfer mechanism indicated that the whole drying process conforms to the microwave radiation mechanism and the basic principle of electromagnetic heating. In the case of low temperatures and thinner slice sizes, the more polysaccharide content was retained; The total phenol content peaked when the slice thickness was 5 mm; The increase of slice thickness was not conducive to the retention of total flavonoids content. The potent antioxidant capacity was detected at a temperature of 40 °C, with slice thickness having a negligible effect on this capacity; Low temperatures were beneficial for the preservation of active ingredients. Compared with the scanning electron microscope, the structure appeared more uniform at a temperature of 50 °C. Based on the analysis of the kinetic characteristics of microwave vacuum drying of Astragalus and the quality achieved under various drying conditions, the results of the study can provide valuable guidance for controlling the quality of microwave vacuum drying of Astragalus under different drying requirements.

Evaluation of microwave vacuum drying combined with explosion puffing drying and compared with microwave vacuum drying and hot-air drying by the quality of the dried apple slices

Evaluation of microwave vacuum drying combined with explosion puffing drying and compared with microwave vacuum drying and hot-air drying by the quality of the dried apple slices

Polysaccharides from Seedless Chestnut Rose (Rosa sterilis) Fruits: Insights into Innovative Drying Technologies and Their Structural Characteristics, Antioxidant, Antiglycation, and α-Glucosidase Inhibitory Activities.

The selection of an optimal drying method is essential for extending the shelf life and enhancing the quality of Rosa sterilis fruits. This study investigated the effects of both innovative (microwave vacuum drying and infrared drying) and traditional (freeze-drying and hot air drying) techniques on the structural characteristics and bioactivities of polysaccharides from R. sterilis fruits (RSPs). Four different RSPs were obtained from fruits dried using these methods. Results demonstrated that the structural characteristics and bioactivities of RSPs varied significantly with the drying method. Notable differences were observed in extraction yield, total sugar, uronic acid content, monosaccharide molar ratios, molecular weight distribution, particle size, thermal stability, and microstructures of RSPs. Despite these variations, the types of constituent monosaccharides and major glycosidic linkages remained consistent across all methods. Notably, RSPs obtained via microwave vacuum drying (RSPs-MVD) showed a higher uronic acid content and lower molecular weight, and exhibited stronger in vitro antioxidant, α-glucosidase inhibitory, and antiglycation activities. These findings suggest that microwave vacuum drying is an effective pre-drying technique for extracting RSPs, making them suitable as bioactive ingredients in functional foods and pharmaceuticals for managing diabetes mellitus and its complications.