Optimization of Microwave-Vacuum Drying of Button Mushrooms Using Response-Surface Methodology

Button mushrooms (Agaricus bisporous) were dried in a microwave-vacuum dryer up to a final moisture content of around 6% (d.b.). The effect of microwave power level (115 to 285 W), system pressure (6.5 to 23.5 kPa), and slice thickness (6 to 14 mm) on drying efficiency and some quality attributes (color, texture, rehydration ratio, and sensory attributes) of dehydrated mushrooms were analyzed by means of response surface methodology. A rotatable central composite design was used to develop models for the responses.Analysis of variance showed that a second-order polynomial model predicted well the experimental data. The system pressure strongly affected color, hardness, rehydration ratio, and sensory attributes of dehydrated mushrooms. A lower pressure during drying resulted in better quality products. Optimum drying conditions of 202 W microwave power level, 6.5 kPa pressure, and 7.7 mm slice thickness were established for microwave vacuum drying of button mushrooms. Separate validation experiment was conducted at the derived optimum conditions to verify the predictions and adequacy of the models.     

Production of Crispy Granules of Fish: A Comparative Study of Alternate Drying Techniques

Three alternate dying methods—vacuum drying (VD), vacuum microwave drying (VMD), and pulse-spouted vacuum–microwave drying (PSVMD)—were examined experimentally for their potential as an industrial scale technology to produce granules of fish. Drying kinetics as well as key quality parameters such as expansion ratio, texture, color, sensory characteristics, and microstructure of crispy granules produced by these drying techniques were examined. Results showed that the drying time is reduced with an increase in microwave power level and with reduced pressure as expected. The quality of the granules is affected by the drying method and the operating parameters employed. Granules obtained using PSVMD at a microwave power density of 6.0 W/g displayed optimal quality required for the commercial product accepted by consumers.     

Analysis of Energy Consumption in Drying Process of Biomaterials Using a Combined Unsymmetrical Double-Feed Microwave and Vacuum System (CUMV)—Case Study: Tea Leaves

An energy analysis of drying of biomaterials (tea leaves) was conducted on a combined unsymmetrical double-feed microwave and vacuum system (CUMV) to optimize the operating conditions and quality of the products. Tea leaves were dried from an initial moisture content of 172 to 7% (db). An energy consumption model based on the first law of thermodynamics was developed to evaluate energy efficiency. The influences of microwave power, vacuum pressure, and microwave operation modes on energy consumption were investigated in detail. The results showed that energy consumption as well as energy efficiency were strongly dependent on vacuum pressure and microwave power. Energy consumption and color parameters of the tea leaves were compared at different drying conditions. In particular, the experiments were carried out at different microwave powers (800 and 1,600 W) at a frequency of 2,450 MHz and different vacuum pressures (535 and 385 torr) to investigate the effects of these factors on the microwave–vacuum drying.     

Drying Characteristics and Quality of Restructured Wild Cabbage Chips Processed Using Different Drying Methods

The drying characteristics of restructured wild cabbage chips dried using microwave vacuum (MVD), hot air (AD), and microwave freeze drying (MFD) were compared. Some of the key quality parameters of restructured wild cabbage chips such as fracturability and color and sensory characteristics were measured. Results showed that the drying time was reduced with the increase of microwave power (MVD/MFD) and in the case of air drying by the temperature (AD). Drying time was the shortest in the MVD process. Optimal quality of dried chips was obtained with the MFD process at a microwave power level 2.0 W/g.     

Microwave Finish Drying of Osmotically Dehydrated Cranberries

Abstract

Combined microwave and hot-air drying characteristics was studied for the drying of cranberries that had been previously partially dehydrated by osmosis in a high fructose corn syrup (76°Brix). A 750 W 2450 MHz microwave oven was used to dry cranberry samples from 57% to 15% moisture content using three different power densities (0.75, 1.0, 1.25 W/g of initial cranberries) and two different power cycles (30 s On/30 s Off and 30 s On/60 s Off). All combinations of these variables were tested in triplicate. Quality of the cranberries was measured using a universal testing machine, chromameter, and with the use of a taste test panel. Drying times ranged from 2.2 to 5.0 h. Power times and power cycles affected the drying time and the quality of the dried cranberries. Lower power densities resulted in cranberries with higher quality. High power densities (125 W/g) resulted in the burning of some cranberries.     

Effects of Microwave-Assisted Hot Air Drying and Conventional Hot Air Drying on the Drying Kinetics,Color, Rehydration,and Volatiles of Moringa oleifera

In this study, the fresh Moringa oleifera pods (Drumsticks) were dehydrated by microwave-assisted hot air drying (MAHD) and conventional hot air drying methods. The samples were dried at three different temperatures, viz. 50, 60, and 70°C, with and without the application of microwaves. Microwave power density of 1 W/g was used for the MAHD. The final moisture content was targeted as 13% wb. The drying curves and drying rate curves were plotted and compared. The kinetics of drying obtained experimentally were correlated with the Page equation. The constants K and N of the Page equation were determined to predict the drying kinetics for varying conditions. The quality attributes, namely, color, rehydration ratio, and volatile compounds, were analyzed and compared with that of the fresh Moringa pods. The volatile compounds were analyzed using z-Nose (an electronic nose; Electronic Sensor Technology, Newbury Park, CA) and bioactive molecules were analyzed using gas chromatography–mass spectrometry. The results showed that the MAHD method had significantly (P < 0.05) reduced the loss of volatiles during drying. Also, MAHD preserved most of the bioactive molecules when compared to the conventional hot air drying method. The samples dried at 50°C using MAHD were the best in terms of all of the quality attributes tested in this study. Also, the results established that the z-Nose can be used as a quick and inexpensive means to assess the effect of different process parameters on the aromatic quality of the product and quantitatively classify quality based on aroma.     

Optimization of Parameters for Microwave-Assisted Foam Mat Drying of Blackcurrant Pulp

Both analysis and optimization of parameters of microwave-assisted foam mat drying (MAFM), viz. microwave power, pulp load, drying time, and pulp thickness, for the dehydration process of blackcurrant pulp were performed in a household microwave oven. During MAFM drying, microwave power, pulp load, and drying time have positive effects on both vitamin C and anthocyanin content of blackcurrant pulp up to a certain level then a negative trend is observed. The increase of microwave power and decrease of pulp load accelerate the dehydration of blackcurrant pulp. The pulp thickness has a significant positive effect on both vitamin C and anthocyanin content of blackcurrant pulp. The optimum parameters valid for MAFM drying of blackcurrant pulp are as follows: microwave power of 560 W, pulp load of 65 g, drying time of 8 min, and pulp thickness of 4.46 mm. MAFM drying is a potential method for dehydrating blackcurrant pulp.     

Optimization of Osmotic Dehydration of Potato Cubes Under Pulsed Microwave Vacuum Environment in Ternary Solution

Optimization of the process parameters for osmotic dehydration of 12.2-mm potato cubes was carried out using response surface methodology. The experiments were conducted using a central composite rotatable design (CCRD) with four factors, viz. sucrose concentration (27.5–42.5% w/w), salt concentration (7.5–12.5% w/w), total osmosis time (26.25–68.75 min), and microwave power density for the initial 4 min (0.375–1.125 W/g of total weight of solution and potato cubes) at two levels each to take into account the individual and interaction effects of the factors. A sample-to-solution ratio of 1:10 and pressure of 0.16 kPa for the initial 4 min were kept constant throughout all of the experiments. It was found that the linear effects of all factors on the water loss (WL) and solids gain (SG) were highly significant. The optimum condition was found at a sucrose concentration of 36.35%, salt concentration of 12.50%, osmosis time of 68.72 min, and microwave power density of 0.38 W/g for the initial 4 min, with a WL of 37.26% initial weight and SG of 8.74% initial weight. The drying of potato cubes was carried out using hot air, microwave–vacuum, and osmotic microwave–vacuum drying methods. It was found that potato cubes dried by combined osmotic microwave–vacuum had better sensory qualities.     

Drying Kinetics of Tomato Slices in Vacuum Assisted Solar and Open Sun Drying Methods

A lab model vacuum-assisted solar dryer was developed to study the drying kinetics of tomato slices (4, 6, and 8 mm thicknesses) compared with open sun drying under the weather conditions of Montreal, Canada. The drying study showed that the time taken for drying of tomato slices of 4, 6, and 8 mm thicknesses from the initial moisture content of 94.0% to the final moisture content of around 11.5 ± 0.5% (w.b.) was 360, 480, and 600 min in vacuum-assisted solar dryer and 450, 600, and 750 min in open sun drying, respectively. During drying, it was observed that the temperature inside the vacuum chamber was increased to 48°C when the maximum ambient temperature was only 30°C. The quality of tomato slices dried under vacuum-assisted solar dryer was of superior quality in terms of color retention and rehydration ratio. The drying kinetics using thin-layer drying models and the influence of weather parameters such as ambient air temperature, relative humidity, solar insolation, and wind velocity on drying of tomato slices were evaluated.     

Modeling Microwave Vacuum Drying Kinetics and Moisture Diffusivity of Carrot Slices

Carrot slices of 3.5 mm thickness were dried in a laboratory microwave vacuum dryer at five different microwave power density levels of 2, 4.66, 7.33, 10, and 12.66 W/g and at three vacuum chamber pressure levels of 6.66, 19.98, and 33.3 kPa to 4–6% d.b. moisture content. Inside the dryer the sample holding plate was rotated with the speed of 4 rpm for uniform microwaves application. The drying rates were increased with the increase in microwave power density at all pressure levels and the Page model was found to be the most suitable model to predict the drying behavior of carrot slices at all process conditions. The Page model drying rate constant (k, min^?1) showed high correlation with microwave power density at constant pressure by a power law equation and showed a logarithmic relationship with the microwave power density and pressure. Similar to the drying rate constant, the average moisture diffusivity at constant pressure was found to be function of microwave power density by power law equation as well as was also dependent on the power density and pressure by a logarithmic relationship.     

Thin-Layer Drying of Green Peas and Selection of a Suitable Thin-Layer Drying Model

The thin-layer drying of three varieties of green peas was carried out in hot air-drying chamber using an automatic weighing system at five temperatures (55–75°C) and air velocity of 100 m/min. The green peas were blanched and sulphited before drying. The variety Pb-87 dried at 60°C was judged to be best for quality on the basis of sensory evaluation and rehydration ratio. The Thomson model was found to represent thin-layer drying kinetics within 99.9% accuracy. The effective diffusivity was determined to be 3.95 × 10^?10 to 6.23 × 10^?10 m²/s in the temperature range of 55 to 75°C. The activation energy for diffusion was calculated to be 22.48 kJ/mol. The variation in shrinkage exhibited a linear relationship with moisture content of the product during drying. The Dincer number at drying air temperature 60°C and drying air velocity 100 m/min was determined to be 2,838,087. The difference between temperatures of drying air and that of green pea kernels was found to decrease with drying time for all the drying temperatures taken for investigation.     

Optimizing Drying Conditions for the Microwave Vacuum Drying of Enzymes

The aim of this study was the methodological use of experimental planning for the optimization of microwave vacuum drying of enzymes using α-amylase as a model. A factorial in star designwas used to optimize the microwave vacuum–drying process, and the variables were power output and vacuum pressure. The material dehydrated by this technique was analyzed with regard to its enzymatic activity, water activity, and moisture content. Response surface methodology was used to estimate the main effects of vacuum pressure and power on the enzymatic and water activities. The experimental in star design revealed that microwave vacuum drying is influenced mainly by power. The dehydrated product showed high enzymatic activity and low water activity.     

Freeze Drying of Apple Slices with and without Application of Microwaves

In this study, Fuji apple slices were dehydrated using freeze drying (FD) combined with microwave assisted with vacuum drying (VMD). The optimal parameter for the diversion point of moisture content from FD to VMD process was at the moisture level of 21%, and for VMD the optimal parameter for vacuum pressure was at 9.15 kPa and microwave power density was at a level of 3.18 w/g. The results show that the two-step technique can significantly reduce total FD time required by up to 40%, while the nutritional value of the dried apple chips remained unchanged compared to FD used alone.     

Drying of Burdock Root Cubes Using a Microwave-Assisted Pulsed Spouted Bed Dryer and Quality Evaluation of the Dried Cubes

Burdock cube samples were dried using hot air and microwave pulsed spouted bed drying (MPSBD). Hot air drying was carried out at three temperatures (70, 80, and 90°C). MPSBD was carried out at three microwave power levels (1.0, 2.0, and 3.0 W/g). The results showed that MPSBD samples dried at 2.0 W/g for 30 min and at 1.0 W/g for 40 min had desirable color, flavor, and textural attributes. Gas chromatography–mass spectrometry results showed that the samples dried using MPSBD were richer in flavor compounds, especially in esters, compared to the hot air–dried samples.     

Microwave Drying Kinetics of Okra

In this work, the effects of power level and sample mass on moisture content, moisture ratio, drying rate, and drying time of Turkey okra (Hibiscus esculenta L.) were investigated using microwave drying technique. Various microwave power levels ranging from to 180 to 900 W were used for drying of 100 g of okra. To investigate the effect of sample mass on drying, the samples in the range of 25 to 100 g were dried at microwave power level of 360 W. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content. Among of the models proposed, Page's model gave a better fit for all drying conditions used. The activation energy for microwave drying of okra was calculated using an exponential expression based on Arrhenius equation and was found to be 5.54 W/g.     

Drying uniformity analysis of pulse-spouted microwave–freeze drying of banana cubes

This article reports the investigation of the drying uniformity of a new drying technique called pulse-spouted microwave–freeze drying. A computer vision technique and mathematical statistics were used to evaluate the drying uniformity. The results show that low microwave power results in prolonged drying time (the drying time of 1 W/g was 6 h, which was longer than that for 2 and 3 W/g), whereas spouting time and the time interval show less influence on the drying time. Analysis from infrared camera photos reveals that lower microwave power, longer spouting interval, and longer spouting time could improve the temperature distribution. Sample 4 (power: 2 W/g, time: 3 s, interval: 300 s) had the best temperature distribution uniformity.     

Comparison of Three New Drying Methods for Drying Characteristics and Quality of Shiitake Mushroom (Lentinus edodes)

This articles provides results of an experimental investigation of three hybrid drying technologies on the drying characteristics and key quality parameters of shiitake mushroom (Lentinus edodes). The drying techniques tested at the laboratory scale are mid-infrared-assisted convection drying (MIRCD), hot air coupled with radio frequency drying (HCRFD), and hot air coupled with microwave drying (HCMD). For comparison, the standard drying technique using hot air was also tested. The quality parameters include texture, color, rehydration rate, shrinkage, nutrient retention, microstructure, etc. These four drying tests were conducted at fixed air temperature (60°C), and the power level for HCRFD, MIRCD, and HCMD was fixed at 4 W/g. The results showed that hot air coupled with microwave drying gave the shortest drying time, and mid-infrared-assisted convection and hot air coupled with radio frequency drying showed better color attributes and nutrient retention. Under the conditions tested, mid-infrared-assisted convection drying yielded minimal shrinkage (maximal rehydration) and lower hardness upon rehydration. The uniform honeycomb network and less collapsed structure of MIRCD samples can be used to explain these better quality characteristics.     

Optimization of Microwave-Vacuum Drying Parameters of Saskatoon Berries Using Response Surface Methodology

A combined microwave and vacuum system was used to dry the Saskatoon berries (Amelanchier alnifolia). A central composite rotate design and response surface methodology were used to determine the influence of process variables (microwave power, drying time, and fruit load) and arrive at optimal processing conditions to reduce the moisture content and water activity of the berries to a safe level. It is concluded that the yield of moisture content and water activity can be reduced to 20% and 0.50, respectively, for microwave power 5.7–6 kW, drying time 51.5–55 min, and fruit load 10–9.75 kg.     

A Comparative Study on the Effects of Microwave and High Electric Field Pretreatments on Drying Kinetics and Quality of Mushrooms

This research evaluated the effects of microwave and high-voltage pretreatments on convective freeze drying of mushrooms (Agaricus bisporus) independently. The effect of the microwave (5 W/g for 5 min) and high electric field (HEF; 430 kV/m for 15 min) as pretreatments on enhancement of the drying rates during subsequent drying and the value addition due to the above pretreatments on the quality of the final dehydrated products were investigated. An exponential mathematical model was developed by fitting the drying kinetics to the Page equation to predict the effects of the pretreatments on the drying kinetics of the mushrooms. The parameters considered for the evaluation of product quality project included color, texture, shrinkage properties, and rehydration ratio of the dried mushrooms. The drying rate of HEF-pretreated mushrooms was found to be unaffected overall when compared to the control and the HEF pretreatment resulted in better quality product and less overall shrinkage. Freeze drying of the pretreated mushrooms was found to result in slower drying rate but better overall quality and rehydration ratio.     

Characterization and Process Optimization of Microwave Drying of Plaster of Paris

The changes in the characteristics of plaster of Paris (pop) during drying operation under microwave irradiation conditions, namely surface morphology, effective moisture diffusivity, and absorption of microwave, were studied. The drying characteristics and kinetics of the process during microwave drying of plaster were studied for rectangular-faced cuboids (80 × 70 × 15, L × B × H in mm) through various drying parameters like microwave power input, initial moisture content, and drying time. Further, the experimental data on moisture ratio of plaster for different operating conditions were obtained and the optimization of the microwave drying process parameters was performed with response surface methodology (RSM) by considering all the above-said independent variables. Based on the RSM analysis, the optimum values of the process variables were obtained as: initial moisture content (A) 60%; microwave power input (B) 180 W; and drying time (C) 480 S.