Vacuum Drying Research Articles

Prevention of the Quality Degradation of Antarctic Krill (Euphausia superba) Meal through Two-Stage Drying.

To achieve a krill meal of high quality, a two-stage drying involving hot-air drying and vacuum drying was investigated. Five experimental groups were established according to the different drying conditions in the second stage, including 95 °C and 101 kPa, 95 °C and 60 kPa, 75 °C and 101 kPa, 75 °C and 60 kPa, and 75 °C and 20 kPa. The results showed that reducing the drying temperature and vacuum pressure in the second stage had a significant impact on the drying characteristics, sensory quality, and bioactive compounds of krill meal. Among all five groups, the drying condition of 75 °C and 60 kPa maintained a high drying rate while preserving a phospholipid content of 30.01 mg/kg and an astaxanthin content of 37.41 mg/kg. It also effectively reduced the isomerization of astaxanthin and the oxidation of unsaturated fatty acids. These results suggested that the two-stage drying method may contribute to the production of high-quality krill meal.

Superhydrophobic Highly Flexible Triple-Network Polyorganosiloxane-Based Aerogels for Thermal Insulation, Oil-Water Separation, and Strain/Pressure Sensing.

Polyvinylpolymethylsiloxane (PVPMS)/polydimethylsiloxane (PDMS) copolymer aerogels were synthesized via consecutive radical polymerization and cohydrolytic polycondensation of vinylmethyldimethoxysilane and dimethyldimethoxysilane, followed by supercritical drying or ambient pressure drying. The resultant PVPMS/PDMS copolymer aerogels exhibit a highly porous, tunable triple-network structure consisting of interlinked hydrocarbon polymers, PVPMS and PDMS. These aerogels display superhydrophobicity (151°), low density (109 mg cm-3), low thermal conductivity (29.8 mW m-1 K-1), and adjustable pore structure. The combination of good machinability, low thermal conductivity, excellent compressive elasticity and bending flexibility, and efficient organic solvent adsorption gives these aerogels broad application prospects in thermal insulation and oil-water separation. In addition, PVPMS/PDMS/carbon nanotube (CNT) composite aerogels were obtained by incorporating the conductive CNTs, followed by vacuum drying. The resultant PVPMS/PDMS/CNT composite aerogel exhibits high sensitivity with a broad pressure sensing range in strain and pressure sensing applications.

Multiscale experimental insights into vacuum drying of sludge for enhanced energy efficiency and emission control

This study provides a comprehensive analysis of the vacuum drying process for sludge drying, with a focus on optimizing energy efficiency and emission control. The study used both lab-scale static and pilot-scale vacuum drying systems to test various parameters like vacuum levels, heat source temperatures, and sludge thicknesses. The results indicated that optimal drying conditions were achieved at a vacuum level of −0.06 MPa, a heat temperature of 140 °C, and a sludge thickness of 3.4 mm, where the drying rate reaches 0.13278 g·g−1·min−1. The study underscores the significant influence of vacuum level, temperature, and sludge thickness on drying rates. The Page model was used to analyze drying kinetics, elucidating how changes in these parameters affect drying characteristics. Furthermore, the study also examined the pollutant emissions and energy efficiency at the pilot scale. It found that high vacuum environments could efficiently dry sludge using low-temperature heat source, leading to average energy consumption per unit evaporation of 3020.29 kJ/kg, which is lower compared to traditional methods. By harnessing low-grade industrial waste heat, this can be further reduced to 875.76 kJ/kg. This study offers valuable insights for sustainable sludge management systems, highlighting the environmental and economic benefits of vacuum drying technology. The detailed experimental approach and thorough analysis make a significant contribution to the field of the sludge drying.

Combined effects of low pressure superheated steam drying and vacuum drying on sugar reduction and quality attribute in mango (Mangifera indica L.) slices

Abstract Consumers paying more attention to physical health has led to an increasing market demand for low-sugar dried fruit products. The quality of products dried via low pressure superheated steam drying (LPSSD) is not only superior to those dried via conventional hot air or vacuum drying (VD), but also has the potential to reduce sugar content. In order to elucidate the mechanism of reducing the sugar of mango slices by LPSSD and obtain low-sugar dried mango slices, the combined effect of LPSSD–VD on mango slices was studied and an evaporation experiment of a sugar solution in a low pressure superheated steam environment was performed. This study revealed that the sugar reduction of mango slices was mainly due to the superheated steam carryover phenomenon in the second half of the constant-temperature stage and the occurrence of Maillard reaction during LPSSD. The quality attributes of mango slices dried using LPSSD–VD was improved compared with LPSSD and VD. As a result, LPSSD–VD could be used to regulate the sugar content in dried fruit and provide a theoretical basis for the production of low-sugar preserved fruits.

Polymer Matrix and Manufacturing Methods in Solid Dispersion System for Enhancing Andrographolide Solubility and Absorption: A Systematic Review.

Background: Andrographolide (ADG) has poor aqueous solubility and low bioavailability. This study systematically reviews the use of solid dispersion (SD) techniques to enhance the solubility and absorption of ADG, with a focus on the methods and polymers utilized. Methodology: We searched electronic databases including PubMed, Web of Science, Scopus®, Embase and ScienceDirect Elsevier® up to November 2023 for studies on the solubility or absorption of ADG in SD formulations. Two reviewers independently reviewed the retrieved articles and extracted data using a standardized form and synthesized the data qualitatively. Results: SD significantly improved ADG solubility with up to a 4.7-fold increase and resulted in a decrease in 50% release time (T1/2) to less than 5 min. SD could also improve ADG absorption, as evidenced by higher Cmax and AUC and reduced Tmax. Notably, Soluplus-based SDs showed marked solubility and absorption enhancements. Among the five SD techniques (rotary evaporation, spray drying, hot-melt extrusion, freeze drying and vacuum drying) examined, spray drying emerged as the most effective, enabling a one-step process without the need for post-milling. Conclusions: SD techniques, particularly using Soluplus and spray drying, effectively enhance the solubility and absorption of ADG. This insight is vital for the future development of ADG-SD matrices.

Intelligent control of microwave vacuum drying based on online aroma monitoring

Astragalus is a common medicinal food that has many benefits for the human body. Some medicinal components in the astragalus would decompose or volatilize at high temperature. Therefore, vacuum drying at a low temperature is a common post-harvest processing for the astragalus. The components and the internal structure of the astragalus change along with the planting range and the harvest year. Therefore, only trained experts with years’ experience can adjust the vacuum drying parameters properly based on their aroma perception, which is backward in the industrial age. In this study, astragalus aroma in microwave vacuum drying was online measured with an electronic nose. Volatiles were verified with Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Drying temperature was PID controlled to maintain constant values. Microwave power was automatically regulated through a Triac circuit. Vacuum degree was adjusted instantly with a step motor. The physical and chemical quality changes of astragalus in drying process were investigated at various temperature and vacuum conditions. To optimize the drying effects, an Artificial Neural Network-based predictive control was designed to adjust the vacuum degree intelligently. The astragalus from Dingxi City, Gansu Province, China was conducted for experiments. By applying different control strategies, the astragalus quality was greatly improved, including more contents of total polysaccharides，astragaloside, total flavonoid, total saponin as well as the enhancement of beany flavor.

Research on boiling heat transfer of aqueous extracts vacuum drying based on fractal theory

Traditional Chinese Medicine (TCM) aqueous extracts are highly viscous pseudoplastic porous media that boiling during vacuum drying, and the drying mechanism significantly differs from that of conventional solid materials. To reveal the heat transfer mechanism, a simulation model of aqueous extracts nucleate boiling was built based on fractal theory, and the effects of superheat, material temperature, viscosity and contact angle on fractal characteristics and heat transfer were studied. Results demonstrate that within a superheat range from 11 °C and 74 °C, the fractal dimension of active nucleation sites on the drying wall ranges between 1.75 and 1.86. The nuclear boiling heat flux increases with the increase in superheat, material temperature, specific heat capacity, thermal conductivity, and contact angle; or with the decrease in viscosity. The research can offer theoretical guidance for the development of drying processes and the optimization of technology in high viscosity pseudoplastic porous media.

Optimization and Testing of the Technological Parameters for the Microwave Vacuum Drying of Mulberry Harvests

This study focuses on mitigating the decrease in the quality of mulberry after harvest and increasing the value of mulberry products through microwave vacuum drying. The effects of mulberry moisture content on texture properties were investigated, and the test method was optimized through the membership function model and the central composite technique. The influences of the material surface temperature, vacuum degree, and microwave power on the quality of instant mulberry were analyzed comprehensively. A regression model was established to analyze the relationship between each test factor and quality index. The results show that, with increases in the moisture content, both the hardness and chewiness of mulberry present a decreasing trend; when elasticity increases gradually, adhesivity is presented in an inverted V-shaped variation trend, and the cohesiveness remains basically constant. Moreover, the moisture content of mulberry had significant correlations with elasticity, glueyness, chewiness, and hardness (R2 > 0.9). When the moisture content of the samples reached ≤44.07%, the total plate count reached a minimum and changed gradually; thus, the moisture content (44.07%) of mulberry was determined for the technological optimization test. The combination of optimal technological parameters was as follows: material surface temperature = 51.0 °C, vacuum degree = 0.07 MPa, and microwave power = 370 W. Under these optimal technological parameters, the soluble solid content was 42.37%, chewiness was 9.08, and the Vc content was 0.725 mg·(100 g)−1. The average error between the test results and software optimization parameters was 5.88%. The optimized microwave vacuum drying technological parameters improved the drying quality of mulberry significantly. The results can provide theoretical support for the microwave vacuum drying of berries.

Development of nutri-rich powder for pregnant/lactating women

Pregnancy and lactation are the two states, which need increased nutritional demand like protein, calcium, iron etc. in women. The study is part of the effort to provide nutritional food that can be more cost effective for pregnant/lactating women. To cater the elevated demand of nutrition, moth bean and finger millet were selected as major ingredients, being richer sources of iron and calcium respectively. The processing steps like soaking and germination helped to lower anti-nutritional factors. The best germination time was optimized for both, moth bean and finger millet based upon reduction in the phytic acid and trypsin inhibitor activity and increase in amylase activity with optimum yield. The best germination period selected for moth bean and finger millet were 36 h at 30ºC and 24 h at 30ºC respectively with 80% RH. The formulation was optimized using Response Surface Methodology at five levels of three variables viz. moth bean flour, finger millet flour and barley malt extract. The optimized product was prepared by mixing germinated and roasted moth bean (21.98%) and finger millet (19.37%) flours with skim milk and barley malt extract (20%), followed by cooking (100ºC, 5 min.), vacuum drying (70ºC, 700 mm Hg), grinding and sieving. The developed nutri-rich food contained 16.74g protein, 5.70 mg iron, 284.49 mg calcium and 1.8 mg zinc, which can provide very good nutrition as per recommendations by ICMR for pregnant/lactating women. The product cost was around 122 INR per kg and it was shelf stable up to 180 days of ambient storage.

Comparison of different drying technologies for coffee pulp tea: Changes in color, taste, bioactive and aroma components

Drying is a crucial process in the production of tea. The effects of sun drying (SD), hot air drying (HAD), microwave drying (MD), vacuum drying (VD) and freeze drying (FD) on the color, taste, bioactive, and aroma of coffee pulp tea (CPT) were evaluated systematically. The results showed that FD could better retain the original color, total phenolics (4.75 mg/mL), trigonelline (0.31 mg/mL), chlorogenic acid (0.067 mg/mL), protocatechuic acid (0.81 mg/mL), and total soluble sugars (24.33 mg/mL) of CPT, but its drying time was longer (32.56 h), and the taste and flavor were the worst. HAD and SD displayed the highest loss rates of most bioactive components, exceeding 40%. In contrast, MD can better improve the quality of CPT, giving it a better color, superior retention of bioactive components, and the most attractive taste and aroma, and decrease the drying time by 66.1% and 96.5%, respectively. Overall, MD is a promising production method for obtaining high-value-added CPT products.

A comparative assessment of drying kinetics, energy consumption, mathematical modeling, and multivariate analysis of Indian borage (Plectranthus amboinicus) leaves

AbstractIn the current study, four drying methods, namely microwave (MD), vacuum (VD), hot air (HAD), and freeze drying (FD), were compared for drying of Indian borage (Plectranthus amboinicus) leaves for optimum energy consumption and bioactive compounds' retention. Effective moisture diffusivity for MD was about 100 times more than that of HAD and VD. MD at 600 W showed minimum specific energy consumption (4.04 kWh/kg), proving the most suitable drying condition. Moreover, it showed desirable energy values in terms of maximum specific moisture extraction rate (0.265 kg moisture/kWh) and maximum drying efficiency (15.85%). Bioactive compounds' retention in terms of phenols, antioxidants, and flavonoids was better in MD, followed by FD. Mathematical modeling of drying kinetics data revealed proper fitting of three drying models, namely, Aghbashlo, Modified Page‐II, and Page model, for explaining the drying behavior of Indian borage leaves. Multivariate characterization using principal component analysis revealed that FD and MD had a strong effect on bioactive compounds' retention, while VD and HAD showed least effect. Hence, based on optimum energy utilization and bioactive compounds' retention, MD at 600 W was selected for efficient drying of Indian borage leaves.Practical applicationsDrying of Indian borage leaves using microwave drying (MD) resulted in quicker drying with retention of bioactive compounds and color of dried leaves. The energy aspects were also favorable for industrial scale‐up. With due consideration to capacity enhancement in MD, it can prove to be a promising source of drying for culinary, medicinal, and aromatic plants.

Microbial Preservation and Contamination Control in the Baking Industry

The required processes and steps for making bread include technological and innovative concepts. The current trend is the use of less toxic compounds and green methods. Besides lactic acid bacteria and yeast, other microorganisms with unique properties, such as enzymes, new aromas and flavors, exopolysaccharides, and vitamins, among other compounds with beneficial properties, could be added to bread manufacture, improving bread quality and health effects for the consumers. The preservation of microbial cultures and starters is crucial in bread-making. New encapsulation methods, cryoprotectants, spray-drying, fluidized bed drying, and vacuum drying are employed for microorganism cultures that will be used as starters or biological additives in fermentation. A development is observed in the antimicrobial methods used as bread preservatives, and studies with plant extracts and essential oils have been proposed and introduced, replacing chemical agents, such as propionate, within the clean-label bread formulations concept. Baking science is a growing research line that incorporates innovative methods, biological additives, new methods, and processes focusing on microbiological protection.

Comparison of different drying technologies for kiwifruit pomace: Changes in physical characteristics, nutritional properties and antioxidant capacities

The objective of this study was to evaluate the impacts of different drying technologies including microwave drying (MD), vacuum microwave drying (VMD), sun drying (SD), vacuum drying (VD), hot air drying (HAD), and vacuum freeze drying (VFD) on the physical characteristics, nutritional properties and antioxidant capacities of kiwifruit pomace in order to realize by-product utilization and improve energy efficiency. Results showed that both MD and VMD significantly reduced drying time by >94.6%, compared to traditional thermal drying which took 14–48 h. MD exhibited the highest content of soluble dietary fiber (9.5%) and the lowest energy consumption. Furthermore, VMD resulted in the highest content of vitamin C (198.78 mg/100 g) and reducing sugar (73.78%), and the antioxidant capacities ranked only second to VFD. Given the financial advantages and product quality, VMD was suggested to be advantageous technology in actual industrial production.

Effects of Different Drying Methods on Drying Characteristics, Microstructure, Quality, and Energy Consumption of Apricot Slices.

An appropriate drying method is crucial for producing high-quality dried apricots. In this study, the effects of four drying methods, hot air drying (HAD), infrared drying (IRD), pulse vacuum drying (PVD), and vacuum freeze-drying (VFD), on the drying kinetics and physical and nutritional characteristics of apricot slices were evaluated. PVD required the shortest time (16.25 h), followed by IRD (17.54 h), HAD (21.39 h), and VFD (34.64 h). VFD resulted in the best quality of apricot slices, with the smallest color difference (ΔE = 13.64), lowest water activity (0.312 ± 0.015) and browning degree (0.35), highest color saturation (62.84), lowest hardness (8.35 ± 0.47 N) and shrinkage (9.13 ± 0.65%), strongest rehydration ability (3.58 ± 0.11 g/g), a good microstructure, and high nutrient-retention rates (ascorbic acid content: 53.31 ± 0.58 mg/100 g, total phenolic content: 12.64 ± 0.50 mg GAE/g, and carotenoid content: 24.23 ± 0.58 mg/100 g) and antioxidant activity (DPPH: 21.10 ± 0.99 mmol Trolox/g and FRAP: 34.10 ± 0.81 mmol Trolox/g). The quality of PVD-treated apricot slices was second-best, and the quality of HAD-treated apricot slices was the worst. However, the energy consumption required for VFD was relatively high, while that required for PVD was lower. The results of this study provide a scientific basis for the large-scale industrial production of dried apricots.

Effects of combined drying techniques and cellulase hydrolysis on the nutritional value and sensory properties of shiitake mushrooms (Lentinus edodes)

Dried shiitake mushrooms offer rich nutritional value and unique sensory properties, prompting further investigation. The effects of different drying techniques (hot air drying (HAD), infrared hot air drying (IRHAD), pulsed vacuum drying (PVD), vacuum freeze drying (VFD), and natural drying (ND)) combined with enzymatic hydrolysis on the release of flavor compounds and nutrients from shiitake mushrooms were explored. The combination of HAD with cellulase hydrolysis yielded notably high levels of umami amino acids (5.4723 ± 0.1501 mg/g) and 5′-nucleotides (4.0536 ± 0.0062 mg/g), and superior volatile flavors. Combined with cellulase hydrolysis, IRHAD achieved the highest level of total sugars (6.57 ± 0.34 mg/mL), VFD resulted in the greatest soluble protein content (153.21 ± 0.23 μg/mL), PVD yielded the highest total phenolics content (93.20 ± 0.41 μg GAE/mL), and ND produced the maximum reducing sugar content (5.79 ± 0.13 mg/mL). This study addresses crucial gap in the post-drying processing of shiitake mushrooms, offering valuable insights for further product development of shiitake mushrooms.

Evaluating How Different Drying Techniques Change the Structure and Physicochemical and Flavor Properties of Gastrodia elata.

We evaluated the drying characteristics and structure, as well as the physicochemical and flavor properties, of G. elata treated by hot-air drying (HAD), vacuum drying (VD), freeze drying (FD), microwave drying (MD), and microwave vacuum drying (MVD). We found that MD and MVD showed the shortest drying times, while FD and MVD were able to better retain the active ingredients and color of the samples. However, the different drying methods did not change the internal structure of G. elata, and its main components did not fundamentally change. In addition, E-nose and HS-SPME-GC-MS effectively differentiated the volatile components, and 36 compounds were detected by HS-SPME-GC-MS. Of these samples, alcohols and aldehydes were the main substances identified. In particular, MVD samples possessed the most species of organic volatiles, but the FD method effectively eliminated pungent odors from the G. elata. Overall, MVD shows the most obvious advantages, improving drying rate while maintaining the original shape, color, and active components in G. elata. Ultimately, MVD is the preferred method to obtain high-quality dried G. elata, and our drying-method characterizations can be used to investigate similar structural and chemical changes to similar herbs in the future.

Cover Image

The cover image is based on the Research Article Effects of ultrasonic power on drying kinetics and product quality of licorice extract during ultrasound‐assisted vacuum drying by Xuecheng Wang et al., https://doi.org/10.1002/jsfa.13283. image

Innovative methods of drying composite materials in vacuum

This work investigates innovative methods of vacuum drying of composite materials, providing improved preservation of physical and mechanical properties, reduced processing time, and lower energy consumption. A review of modern composite drying technologies is conducted, and the advantages of the vacuum method are identified. The methodoogy of an experimental study of the effectiveness of vacuum drying is presented, utilizing composite material samples and analyzing their properties before and after processing. The obtained results showed a significant improvement in strength characteristics and a 30 % reduction in drying time compared to traditional methods. A 25 % decrease in energy consumption was also observed. Statistical analysis confirmed the significance of differences in results between different processing methods. The advantages of vacuum drying are discussed, related to more uniform moisture removal and prevention of thermal damage to composites. Conclusions are drawn about the prospects of applying the developed methods in industrial production to improve quality and reduce costs.

Effect of drying temperatures and using prebiotics on the physicochemical and microbiological properties as well as consumer acceptance of probiotic-enriched Lor cheese snacks produced by vacuum drying

This study assessed the impact of drying temperatures (37 °C, 45 °C, and 55 °C) and using prebiotics (inulin or maltodextrin) on the physicochemical and microbiological properties as well as consumer acceptance of probiotic-enriched Lor cheese snacks produced by vacuum drying. The Lor cheese snacks produced using Lactobacillus acidophilus DSM 20079 as probiotic bacteria were stored at 25 °C for 60 days. The moisture content as well as aw and titratable acidity values of the Lor cheese snack produced by vacuum drying at 37 °C were higher than those produced by vacuum drying at both 45 °C and 55 °C. The highest fracture force values were determined in the Lor cheese snacks produced using maltodextrin and by vacuum drying at 55 °C. The L* and a* values decreased and the b* values of the Lor cheese snacks increased with the increasing drying temperature, while the type of prebiotic used did not significantly affect the L*, a*, and b* values. The taste, aroma, texture, and overall acceptability scores in the Lor cheese snack samples produced by vacuum drying at 45 °C and 55 °C were found to be similar. The counts of L. acidophilus were above 8.0 and 6.0 log cfu/g in the Lor cheese snacks produced by vacuum drying at drying temperatures of 37 °C and 45 °C, respectively, after 60 days of storage. In conclusion, the present study suggests that the use of maltodextrin and vacuum drying at 45 °C are suitable to produce the Lor cheese snacks considering their physicochemical and microbiological properties as well as consumer acceptance.

Microwave-vacuum drying: Modeling validation of drying and rehydration kinetics, moisture diffusivity and physicochemical properties of dried dragon fruit slices

This study investigated the drying of dragon fruit slices with varying samples (0.5 cm, 1 cm, and 1.5 cm) using a microwave-vacuum dryer at power levels of 400 W, 600 W, and 800 W, under a vacuum pressure of 600 mm Hg. The comprehensive assessment included drying kinetics, effective moisture diffusivity (Deff), rehydration behavior, color changes, and ascorbic acid content. Results indicated a substantial moisture content reduction from an initial 614.28% to an average of 7.14% (dry basis) post-microwave vacuum drying. The Wang and Singh model proved most suitable, exhibiting high R2 values and low RMSE values, providing accurate insights into the drying process. Dragon fruit samples showed Deff values from 4.381 × 10−3 to 4.084 × 10−2 cm2/min, increasing with microwave power level. Rehydration, modeled by the Peleg model, revealed that the highest power level had the highest R2 and lowest RMSE values. Notably, 1.5 cm slices at 400 W exhibited minimal color change (18.32) and retained the most ascorbic acid (6.94 mg/100 g). This study offers valuable insights into dragon fruit drying, highlighting its impact on moisture content, modeling, and product quality.