Microwave Drying Research Articles

The role of environmental air and microwave drying on colour values, bioactive properties and phenolic compounds of jalapeno pepper

SummaryIn this study, the effect of dehydration of some physico‐chemical characteristics, total phenol, flavonoids, antioxidant capacity and phenolic compounds of green and red jalapeno pepper fruits was investigated. The total carotenoid contents of red and green jalapeno pepper samples were reported to be between 14.15 (fresh) and 129.00 μg/g (540 and 720 W) to 2.8 (fresh) and 27.25 μg/g (720 W), respectively. Total phenolic results of red and green jalapeno pepper samples were recorded between 205.83 (fresh) and 343.93 mg GAE/100 g (540 W) to 81.69 (fresh) and 309.88 mg gallic acid equivalent (GAE)/100 g (air drying), respectively. The highest decrease in L* results (brightness) of both red (32.33) and green (36.45) peppers was determined with air drying. Gallic acid, catechin and kaempferol were the predominant phenolic compounds of jalapeno peppers. Gallic acid amounts of red and green jalapeno pepper samples changed between 3.23 (fresh) and 16.20 mg/100 g (air) to 2.41 (fresh) and 9.30 mg/100 g (air), respectively. Also, catechin amounts of both red and green dehydrated jalapeno pepper fruits were determined between 3.24 (fresh) and 106.33 mg/100 g (900 W) to 2.89 (fresh) and 90.05 mg/100 g (air), respectively. Both conventional and microwave drying has caused the reduction of redness for red pepper and greenness for green pepper. The phenolic components of red jalapeno peppers were partially higher than the green ones.

Evaluation of Leaves, Flowers, and Seeds of Coriander (Coriandrum sativum L.) through Microwave Drying and Ultrasonic-Assisted Extraction, for Biologically Active Components

The coriander plant (Coriandrum sativum L.) is well known for its antibacterial and antioxidant properties since it contains a considerable number of bioactive compounds. This property encourages the use of coriander in food because it has many health benefits and preserves food longer. The current study’s objective was to demonstrate the extraction of coriander’s three fractions (leaves, flowers, and seeds) using microwave drying and ultrasonic assistance, in order to identify its distinct functional components. After microwave drying, the highest amounts of ash, fat, fiber, and protein with values 6.39±0.04, 10.10±0.05, 10.14±0.06, and 13.10±0.03%, respectively, were observed in coriander seeds. Among macro- and microminerals analyzed, contents of Ca and Mg were found highest in coriander leaves, with values 689±0.14 and 412±0.04 mg/100 g, respectively, whereas Fe, Zn, and Mn were found highest in seeds with values 15.46±0.02, 3.92±0.02, and 1.29±0.02 mg/100 g. Ultrasonic-assisted ethanolic extracts of microwave-dried coriander leaves presented significantly high (p<0.05) total phenolic contents (253.45±0.12 mg gallic acid equivalent/100 g), total flavonoid contents (98.15±0.09 mg quercetin equivalent/100 g), and total antioxidant activity (47.32±0.04 mg trolox/100 g), followed by seeds, while flowers presented lowest values. Significantly high (p<0.05) antimicrobial activities were exhibited from extracts of coriander seeds, followed by leaves. It was concluded that leaves, flowers, and seeds of coriander all were rich source of nutritional components and bioactives, and microwave drying and ultrasonic-assisted extraction were proved useful techniques for maximum retention of these contents in powders and ethanolic extracts, respectively.

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.

Regeneration behavior of solid desiccants with microwave drying

Regeneration behavior of solid desiccants with microwave drying

Effect of Microwave Pretreatment on the Properties and Microstructure of Low-Concentration Carbon Dioxide Early Cured Cement-Based Materials

The utilization of microwave drying technology has expanded across various sectors due to its rapid processing speed, reduced operation time, lower sample temperatures, and consistent heating. In this research, microwave pretreatment was implemented prior to carbonation curing with low concentrations, and an array of tests including moisture content, compressive strength, carbonation depth, CO2 absorptivity, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were utilized to investigate the effect of microwave pretreatment on the properties and microstructure of cementitious materials under early carbonation curing with low CO2 concentrations. The findings reveal that microwave pretreatment significantly decreases the moisture content within the test specimens, expediting the ingress of CO2 and improving the compressive strength of the specimens. At the same time, the effectiveness of microwave pretreatment in reducing moisture content diminishes as the pretreatment time increases. The absorption of CO2 is relatively rapid in the early stage of carbonation curing, with over 50% of the CO2 absorption occurring within the 0–6 h period of carbonation curing. The hydration products and microstructure of the uncarbonated part inside the specimens are generally consistent with the normal curing state. The formation of CaCO3 contributed to the densification of the specimen by infilling its internal voids, thereby enhancing its compressive strength. Although carbonation curing enlarges the average pore size of the samples, it also serves a filling function, making the samples more compact and reducing the porosity.

Investigating the effects of drying on the physical properties of Kombucha Bacterial Cellulose: Kinetic study and modeling approach

Kombucha bacterial cellulose (KBC), obtained as a by-product of tea fermentation, has potential applications in diverse fields. The high water content and presence of post-fermentation residues necessitate the implementation of suitable drying conditions that can significantly affect the final characteristics of this versatile biopolymer. Thus, to study the effect of different drying methods on its properties, KBC was subjected to microwave drying (180–900 W), hot air oven drying (30–70 °C), and shade drying (25 °C). Additionally, the acquired data were fitted into ten different models to study the drying kinetics of KBC. The dried sheets were then analyzed to study the changes in water absorption and holding capacity, rehydration, surface color, and other physicomechanical properties (UTM, XRD, and contact angle analysis). Hence, optimization of the drying conditions will help reduce the time and cost without compromising any of the intrinsic properties that allow it to be processed into various value-added products.

The Effects of Microwave and Oven Drying on Bioactive Compounds Individual Phenolic Constituents and the Fatty Acid Profiles of Bitter Orange, Mandarin and Grapefruit Peel and Oils

The Effects of Microwave and Oven Drying on Bioactive Compounds Individual Phenolic Constituents and the Fatty Acid Profiles of Bitter Orange, Mandarin and Grapefruit Peel and Oils

Optimized extraction of polyphenols from tea factory waste and cost-effective drying methods for sustainable utilization

This study systematically addresses the significance of polyphenol extraction and preservation from factory tea waste, aiming to unlock its untapped potential by emphasizing sustainability and resource efficiency. Tea, renowned for its rich content of polyphenols and their notable antioxidant properties, serves as a reservoir of valuable organic compounds. However, in the realm of tea processing, a substantial volume of waste is generated, often subject to environmentally detrimental disposal practices. Delving into the substantial waste generated in tea processing, the research optimizes polyphenol extraction parameters using water as a solvent, establishing optimal conditions at 80 °C, 60 min, and a solid-to-liquid ratio of 1:30 (g/mL). At the optimized condition, the recorded polyphenol content was 2635.36 ± 52.07 mg GAE/L, highlighting the efficacy of the established parameters. The study validates the predicted responses of the Response Surface Methodology (RSM) model, identifies major polyphenols through LC-MS, confirms antioxidant activity via DPPH assay, and evaluates the biocompatibility of the tea waste polyphenolic extract with HEK 293 cells through MTT assay. The study employed four distinct drying methods—freeze drying, hot air over-drying, vacuum drying, and microwave drying. To preserve the quality of the TPC in the powder, optimization of drying time and temperature was undertaken. Notably, among these methods, vacuum drying at 50 °C emerged as the most cost-efficient drying option, amounting to $1.77/g of TPC powder, while concurrently maintaining a TPC value of 163.63 ± 5.43 mg GAE/g DW. This sustainable approach holds promise for diverse applications, including nutraceuticals, food preservation, cosmetics, and environmental remediation, aligning with global sustainability goals.

Recognition performance of different artificial neural networks for distinguishing banana slices subjected to different combinations of pretreatment and microwave drying

This study was aimed at assessing the effect of microwave drying at 100, 200, or 300 W on the quality of Cavendish banana slices without pretreatment and with pretreatment using 5% ascorbic acid solution, 5% citric acid solution, 5% gum arabic solution, and ultrasound. Banana slices were imaged using a digital single-lens reflex (SLR) camera. The acquired images were processed to extract texture parameters. The classification models were developed based on image texture parameters selected from a big dataset of 2172 textures of images in different color channels using artificial neural networks. Wide Neural Network, Bilayered Neural Network, Medium Neural Network and three classifiers from the group of function, such as RBF (Radial basis function) Network, Multilayer Perceptron, and WiSARD were applied. Banana slices belonging to 15 classes with different combinations of pretreatment and microwave drying were distinguished with an average accuracy of up to 97.2% for a model built using Multilayer Perceptron. For most models, banana samples microwave-dried at 200 W without pretreatment were classified with the highest correctness. The performed study revealed that the objective, non-destructive, correct, and robust quality assessment of pretreated and microwave-dried banana slices may be performed using image processing and artificial intelligence.

Comparative evaluation of drying methods for struvite produced from electrocoagulated source-separated urine: Implications for quality, energy and cost-effectiveness

Struvite precipitation from source-separated urine is crucial for waste utilization and sustainability. However, after precipitation, the high moisture content of struvite necessitates an additional drying process that can be costly and inefficient. In the present study, the performance of different drying methods—open sun drying, air drying, conventional drying (20–100 °C), and microwave drying (180–720 W) on the quality of struvite obtained from source-separated urine through electrocoagulation using Mg–Mg electrodes were evaluated. It was found that higher temperatures and power in the convective oven and microwave resulted in higher diffusivity (10−9-10−7 m2s−1), leading to reduced drying times. Different models were employed to comprehend the drying mechanism, and the one with the highest correlation coefficient (R2 = 0.99) and the lowest statistical values was selected. The key findings indicated that higher power and temperature levels were more cost-effective. However, characterization of the dried struvite using X-ray diffraction and Fourier-transformed infrared spectroscopy, disintegration of struvite crystals at temperatures above 60 °C in the conventional oven and 180 W in the microwave oven was observed. Based on the results, we conclude that sun drying is a cost-effective and environmentally friendly alternative for drying struvite without compromising its quality.

Sensory properties of rehydrated Toona sinensis shoots after dehydrated by different drying methods and association with gamma-glutamyl transferase reaction

Sulfur-containing compounds are responsible for the aroma of Toona sinensis shoot (TS). In this study, vacuum-freeze-drying (VFD), microwave-drying (MD), and hot-air-drying at 100 and 40 °C (HAD100 and HAD40, respectively), were applied to dehydrate perishable TS for preservation. VFD-TS retained most aroma of fresh/raw TS after rehydration. The content of sulfur-containing compounds reached to 118.00 µg/g with leading by methyl thiirane, (E,E)/(E,Z)/(Z,Z)-bis-(1-propenyl) disulfides, and (Z)/(E)-2-mercapto-3,4-dimethyl-2,3-dihydrothiophenes accounting for 86.33 %. They were undetected in the rehydrated MD-TS and HAD100-TS, as the indigenous enzymes in TS were deactivated under their dehydration conditions. Interestingly, the sulfur-containing compounds was restored by 77.47 % after the TS was treated by gamma-glutamyl transferase (GGT). Thus, the release of sulfur-containing compounds from TS could depend on GGT reaction. It was different from alliaceous vegetables relying on alliinase reaction. The results revealed the aroma formation in TS and provided an approach to enhance the aroma of TS dried by different methods.

Synergistic Effects of Dielectric Barrier Discharge (DBD) Cold Plasma Pretreatment Combined with Microwave Drying on the Physicochemical and Functional Properties of Centella asiatica Leaves

Synergistic Effects of Dielectric Barrier Discharge (DBD) Cold Plasma Pretreatment Combined with Microwave Drying on the Physicochemical and Functional Properties of Centella asiatica Leaves

Differences in monophenolic content and composition of persimmon fruit slices from different regions under fresh and microwave drying

The browning of moon persimmons during the drying process was primarily caused by the oxidation of phenolic compounds. Additionally, microwave drying led to uneven browning of the fruit slices. This study aimed to evaluate effect of microwave drying on the content of 19 monophenolic compounds in moon persimmon fruit slices from six different regions (A1, A2, B1, B2, C1 and C2). The analysis was conducted using ultra-performance liquid chromatography with high-resolution mass spectrometry. The findings indicated that the three primary monophenols with the highest concentrations in fresh moon persimmon fruit slices were gallic acid, phenylalanine and catechin; these concentrations ranged from 0.554 to 6.797 mg/100 g. The distribution of monophenol species was higher in the outer edge region of the fruit slices, with 14 monophenols detected in the C2 region. Microwave drying increased gallic acid content and decreased other monophenol content. Monophenolic compounds under microwave drying underwent autoxidation and also transformed into each other. The B2 region of the fruit slices displayed the earliest occurrence of browning and exhibited the most significant changes in both rate and magnitude of phenolic content. The colour deterioration of moon persimmon fruit slices during microwave drying is related to the change in phenol content, which may be caused by the phenol autoxidation reaction.

Application of a Surface Waveguide in Microwave Drying Units of the Agribusiness Industry

In the last two decades, the electromagnetic field of the microwave range has been successfully introduced into various branches of the agribusiness industry as one of the most promising and advanced technologies for drying manufactured products. In this regard, the article proposes a new microwave irradiation technique for drying various objects based on a surface waveguide’s properties. The paper analyses the main links that make up the surface waveguide as a microwave irradiation system and shows the ways of their implementation. The article describes the advantages of applying a vibratory device for exciting a surface wave, using a re-emitting antenna array, and operating a single conductor with a dielectric coating as a surface waveguide. Such advantages make it possible to introduce microwave drying units with the required distribution of electromagnetic field energy along the irradiated material, small dimensions, high drying quality, and low price.

READY-TO-EAT SNACKS FROM MICROWAVE DRIED RED RADISHES: QUALITY PARAMETERS AND DRYING KINETICS

The aims of this study were to evaluate the microwave drying (MWD) process in radish slices (Raphanus sativus L.) and to select optimal conditions to obtain high quality and nutritious snacks. Mathematical modelling of drying kinetics, energy efficiency and quality of final product (color, antioxidant capacity, total polyphenols, flavonoids and ascorbic acid contents) were determined at 90, 270 and 450 W. The kinetic parameters followed increasing tendency with microwave power (MWP). The Midilli–Kucuk model presented the best fit simulating experimental drying curves and it was used to model the generalized drying curve for the whole MWP range of the performed experiments. High MWP increased the mass transfer and the effective moisture diffusivities, and shortened the drying time until 70.73%. Working at 90W resulted the best MWD treatment that would allow obtaining a radish snack with suitable color, nutritional quality and energy consumption.

Comparison of the Effect of Drying Treatments on the Physicochemical Parameters, Oxidative Stability, and Microbiological Status of Yellow Mealworm (Tenebrio molitor L.) Flours as an Alternative Protein Source

The increasing production of edible insects on an industrial scale makes it crucial to implement appropriate technologies after harvesting to process safe and high quality insect products. The aim of this work was to compare the impact of different drying treatments used in the production of flour from Tenebrio molitor larvae. The larvae were subjected to freeze-drying (FD), conventional drying (CD), microwave drying (MWD), microwave drying without freezing prior blanching (MWDL), and microwave drying with addition of 0.1% butylated hydroxytoluene (BHT) during the blanching of the larvae (MWDA). The studied parameters included water activity (aw), instrumental colour, chemical composition, lipid oxidative processes, antioxidant activity, as well as microbiological status. The freeze-drying and conventional drying of the larvae reduced the aw of the derived flours (p < 0.0001); however, their nutritional profile revealed lower protein (p < 0.0001) and considerably higher fat content (p < 0.0001) compared to the flours after microwave treatments. The conventional drying and microwave treatment with BHT induced significantly darker colour (p < 0.0001) in comparison to the other methods. Despite the advantages of the microwave drying as a fast and energy efficient method, it displayed some negative effects associated with low lipid stability such as higher acid value (AV) and secondary products of lipid oxidation (TBARS) (p < 0.0001). This was also observed in the MWDA flour, indicating a certain pro-oxidative effect of the BHT. Regardless of the drying method, all the flours had a low microbial load.

Evaluation of aroma characteristics of Penaeus vannamei with different drying methods using HS-SPME-GC-MS, MMSE-GC-MS, and sensory evaluation

The effects of microwave drying (MD), hot air drying (HAD), vacuum hot air drying (VD), and vacuum freeze drying (VFD) on the volatile profiles of Penaeus vannamei were investigated. A total of 89 and 94 volatile compounds were identified by headspace solid-phase microextraction-gas chromatography–mass spectrometry (HS-SPME-GC–MS) and monolithic material sorptive extraction gas chromatography–mass spectrometry (MMSE-GC–MS), respectively. Orthogonal partial least squares-discriminant analysis (OPLS-DA) and variable influence on projection (VIP) models were utilized to select characteristic volatiles and key marker compounds (e.g., octanal, 1-octen-3-ol, 2-methyl-butanal, 2-ethyl-furan, and trimethyl-pyrazine) to discriminate among four drying methods. Based on synthesis of odor descriptions and sensory evaluation, it was found that P. vannamei via MD, HAD, and VD greatly reduced the fishy and generated roasted, fatty, and smoked odors. This study systematically analyzed the aroma characteristics of four traditional dried P. vannamei products, which may provide theoretical guidance for industrial production.

Unlocking the potential of oil by-products: Investigating the influence of co-culture fermentation on phenolic acid degradation in side stream blends from oil and dairy industry

According to the newest trends in food waste management, the priority for valorisation of oil and dairy industry by-products was recognised. New approach of blending side streams of plant and animal origin has been proposed for obtaining future foods with improved nutritional value. Major obstacle in valorising sunflower seed cake (SSC) and whey (W) is their perishability and a relatively high content of phenolics contributing to, among others, protein indigestibility. In the study, a new approach of microwave pre-treatment applied for SSC and W blends was used. Its influence on phenolic acids and antioxidant properties after fermentation with co-culture of lactic acid bacteria and yeast was examined. Microwave drying of blends was longer than that of SSC affecting phenolic acids content. Fermentation by L. lactis and K. lactis caused pH decrease and increase in total acidity in 48 h effectively limiting the growth of bacterial contaminants. Fermentation decreased the content of phenolic acids, especially in blend composed of SSC and W (8.75:1; w/w) with the highest content of these constituents (from 1611.3 down to 838.8 mg/100 g dry matter). The study showed the synergistic effect of pre-treatment method and fermentation in terms of reduction in phenolic acids in new food matrices.

Physical and Chemical Properties of Convective- and Microwave-Dried Blackberry Fruits Grown Using Organic Procedures.

This study aimed to evaluate the effect of convective and microwave drying on the bioactive-compounds content of blackberry (Rubus fruticosus) fruits, as well as drying parameters and energy consumption. The fruit was dehydrated in a convective dehydrator at a temperature of 50 °C and 70 °C and in a microwave oven at power levels of 90 W, 180 W and 240 W. The highest amount of anthocyanins, polyphenols and antioxidant capacity were obtained in blackberry fruits that were microwave dried at 90 W and 180 W (46.3-52.5 and 51.8-83.5 mg 100 g-1 dm of total anthocyanins, 296.3-255.8 and 418.4-502.2 mg 100 g-1 dm of total phenolics, and 1.20-1.51 and 1.45-2.35 mmol TE 100 g-1 dm of antioxidant capacity for 90 W and 180 W models, respectively). It turned out that microwave dehydration shortened the processing time and lowered the energy consumption compared to convective drying (a significantly reduced drying time of 92-99% with microwave dehydration). Blackberry fruits dehydrated at 240 W showed the shortest dehydration time (59-67 min), minimal energy consumption (0.23 kWh) and the most efficient diffusion (1.48-1.66 × 10-8 m2 s-1).

Comparative study on microwave and tray drying of beef: Effect of partial salt replacement on drying kinetics and structural characteristics

Beef cuts were dried by tray drying (TD), microwave drying (MD), and TD+MD. Salting as pre-treatment was carried out with NaCl or NaCl+KCl salts to evaluate the effect of sodium reduction. The beef was divided into nine groups: three were subjected to TD, MD, and TD+MD; for the other six groups, dry salting was applied with 100% NaCl or 50% NaCl + 50% KCl, followed by MD, TD, or TD+MD. Processing times of TD, MD, and TD+MD were about 660, 250, and 300 min, and effective diffusivities (Deff) were 1.33 × 10-8, 3.88 × 10-8, and 3.57 × 10-8 m2/s, respectively. Compared with TD, the MD procedure resulted in significantly harder texture and lower rehydration ratio (p < 0.05). SEM images of dried beef indicated fractures and disruption after TD, while a compact structure was obtained with MD. Both salt types contributed a softer texture in rehydrated MD, but KCl did not change the hardness values of dried meat. MD could have great potential for drying meat by reducing drying time, and KCl could be applied as a substitute for NaCl without adversely affecting the structural quality.