Optimizing Drying Conditions for Microwave-Vacuum (MIVAC®) Drying of Russet Potatoes (Solanum tuberosum)

MIVAC® combines microwave heating with vacuum drying. Microwave power is modulated based upon product temperature and can limit overheating compared to other microwave-vacuum methods. Blanched potatoes were dried at 50, 60, and 70°C for 0 to 150 min. Potatoes dried at 70°C had a lower moisture content in less time compared to potatoes dried at 50 and 60°C, but the color of the dehydrated potatoes was affected due to overheating. Drying at 60°C for 150 min resulted in dried potatoes with acceptable color. Drying at 50°C resulted in dehydrated potatoes of acceptable color; however, it required more time.     

Influence of Osmoconcentration, Continuous High-Frequency Ultrasound and Dehydration on Properties and Microstructure of Rabbiteye Blueberries

Rabbiteye blueberries were osmoconcentrated for 12 h, and for 3 h with and without continuous high-frequency ultrasound (CHFU) and then air dehydrated (70°C, 10 h). Osmoconcentration increased solids gain, moisture loss, soluble solids, and bulk density. Long osmoconcentration for 12 h can be reduced with CHFU with similar results. Scanning electron microscopy (SEM) micrographs indicated that berries without pretreatment suffered the highest degree of tissue collapse. They also had the highest rehydration ratio and may be ideal for use in breakfast cereals. Osmoconcentrated berries may be used as snack food or in cereal bars due to high bulk density and low rehydration ratio.     

Simultaneous Drying and Modification of Properties of Starch Using Vacuum Microwave Treatment

The prospect of modifying starch properties while drying was investigated. Potato starch (18% moisture, dry basis) was vacuum microwave treated for different durations (60 to 600 s) with power ratings of 600, 1,000, and 1,500 W at a reduced pressure of 5,000 Pa (absolute). The drying rate was observed to be partially constant but was accompanied by a curious rise in sample temperature. Under a polarized light microscope, reduction in granule size was noticed, which was confirmed from the bulk density measurements, and this shrinkage may be explained by the loss of constituent water. Water absorption capacity of the treated starch samples was further studied at 55°C. The results showed a sudden increase in the capacity, indicating a reduction in gelatinization temperature of starch. This may be attributed to the change in nature of starch from crystalline to amorphous as shown by X-ray diffractograms and to the cracks developed on the granule surface during treatment seen in the scanning electron microscope images. This modified starch can serve well in the paper and food industry.     

Microwave,Vacuum, and Air Drying Characteristics of Collard Leaves

Collard leaves (Brassica oleracea L. var. acephala) with an initial moisture content of 6.65 on percentage dry basis (%db) were dried by three different drying methods: microwave, air, and vacuum. Samples of fresh leaves, 25 g each, were dried until their moisture was down to 0.1 on a dry basis. The following drying levels were used in each of the drying processes: 350, 500, 650, 750, 850, and 1000 W for microwave drying; 50, 75, 100, 125, 150, and 175°C for air drying; and 0.4, 50, and 100 mmHg at 50 and 75°C for vacuum drying, respectively. Drying times ranged between 2.5 to 7.5 min, 8 to 210 min, and 35 to 195 min for microwave, air, and vacuum drying, respectively. The data obtained compared well with a thin-layer drying model. Microwave drying at 750 W provided optimal results with respect to drying time, color, and ascorbic acid content (vitamin C).     

Shrinkage Characteristics of Potatos Dehydrated Under Combined Microwave and Convective Air Conditions

ABSTRACT

A study of the pysical structure and quality potatoes during microwave and air drying war undertaken. The effect of various experimental variables on volumetric shrinkage including microwove power levels, air temperature and velocity as well as sample geometry was investigated. In both microwave and air drying, the shrinkage of potatoes showed a linear behaviour in relation to different moisture content levels. Experimental data showedthat air velocity and microwave power had a major effect on the degree of shrinkage, also the shrinkage behaviour was independent of sample geometry and air temperature. The use of microwave produced smaller changer in volume (less shrinkage) and henee a better quality finished product.     

Shrinkage Characteristics of Potatos Dehydrated Under Combined Microwave and Convective Air Conditions

A study of the pysical structure and quality potatoes during microwave and air drying war undertaken. The effect of various experimental variables on volumetric shrinkage including microwove power levels, air temperature and velocity as well as sample geometry was investigated. In both microwave and air drying, the shrinkage of potatoes showed a linear behaviour in relation to different moisture content levels. Experimental data showedthat air velocity and microwave power had a major effect on the degree of shrinkage, also the shrinkage behaviour was independent of sample geometry and air temperature. The use of microwave produced smaller changer in volume (less shrinkage) and henee a better quality finished product.     

Studies on Hot Air and Microwave Vacuum Drying of Wild Cabbage

Abstract

Wild cabbage was dehydrated by a combination of hot-air drying and microwave vacuum drying. It showed that the total drying time was reduced by about half while the retention values of the nutrient components and chlorophyll were improved significantly. Microwave/vacuum-dried products had a more porous texture. Finally, microwave drying showed effective bactericidal action in the product with acceptable quality of dried product.     

Studies on Hot Air and Microwave Vacuum Drying of Wild Cabbage

Wild cabbage was dehydrated by a combination of hot-air drying and microwave vacuum drying. It showed that the total drying time was reduced by about half while the retention values of the nutrient components and chlorophyll were improved significantly. Microwave/vacuum-dried products had a more porous texture. Finally, microwave drying showed effective bactericidal action in the product with acceptable quality of dried product.     

A Combination of Freeze Drying and Microwave Vacuum Drying of Duck Egg White Protein Powders

High energy consumption during freeze drying (FD) is a major concern that limits its application on common food product manufacturing. In this research, fresh duck egg white protein (FDEWP) powder and desalted duck egg white protein (DDEWP) powder were obtained by a combined two-stage tandem drying technologies (FD and microwave–vacuum drying [MVD]) in order to reduce energy consumption while maintaining good product quality. The results showed that the drying time for the FDEWP and DDEWP powders was significantly decreased by FD + MVD compared to those obtained by the FD-only process. The FDEWP powders dried by FD + MVD had a better color (higher L* and lower b*), lower apparent density, and lower foaming stability but higher emulsifying index than those dried by FD only. The DDEWP powder dried by FD + MVD had a product quality similar to that of FDEWP powder, suggesting that the DDEWP powder could be widely used as a food ingredient.     

Analysis of Chestnut Cellular Tissue during Osmotic Dehydration,Air Drying,and Rehydration Processes

The analysis of changes in microstructure is very important in order to understand heat and mass transfer processes in biological systems and to evaluate physical properties and the quality of fresh and processed food materials. In this study, chestnut (Castanea sativa M.) samples were submitted to several processes such as osmotic dehydration by immersion in sucrose solution (60% w/w) at 25°C, drying with hot air at 65°C, and rehydration by contact with water at 25°C. The surface cellular tissue of fresh and processed chestnut at different moisture contents was characterized by optical microscopy by means of size (surface area, perimeter, Feret's diameter) and shape (roundness, compactness, and elongation) parameters. The results indicated that during the osmotic dehydration the changes in microstructure can be considered practically negligible and during drying the size of chestnut cells decreased and shape parameters changed (decreasing roundness and compactness and increasing elongation). Finally, during rehydration the cells recovered their size by swelling rapidly (30 min is enough to recover the size of the cells of fresh tissue), achieving at longer times greater sizes than those measured in the fresh chestnut; nevertheless, the shape parameters are not completely recovered (lower compactness and roundness values).     

Microwave and Hot Air Drying of Wood Using a Rectangular Waveguide

In this study, the microwave and hot air drying of wood using a rectangular waveguide (TE₁₀ mode) were investigated experimentally. Most important, this study focuses on the investigation of drying phenomena under a microwave environment. In this analysis, the effects of the irradiation time, hot air temperature, sample thickness, and microwave power level on overall drying kinetics were studied. The results showed that the variations of irradiation time, microwave power level, hot air temperature, and sample thickness played an important role in overall drying kinetics. These findings are significant for further research in similar studies. Further quantitative validation of experimental data could be very useful, especially in providing information for developing high-performance microwave drying processing.     

Effects of Ultrasound and Microwave Pretreatments of Apple Before Spouted Bed Drying on Rate of Dehydration and Physical Properties

Pretreatments of fruits before drying have been proposed as alternative way to improve the quality of dried fruits and reduce drying time. In the present study, the effects of different pretreatments (ultrasound and microwave) on apple cubes prior to spouted bed drying were investigated. Ultrasound pretreatment resulted in a great loss of sugars (25.7% for 15 min) compared to microwave pretreatment, where little rise in sugar content was observed (1.6% at 300 W). Ultrasound pretreatment improved the drying rate more than microwave pretreatment. Nevertheless, microwave-pretreated dried apples were harder and had lower water activity than ultrasound-pretreated ones. Low-frequency nuclear magnetic resonance (LF-NMR) analysis was used to study the water state and revealed that all pretreatments promoted redistribution of water among apple cell compartments and showed that most of the water lost was from the vacuoles. If dried low-calorie fruits are required then ultrasound pretreatment would be preferred.     

Investigating the Commercial Microwave Vacuum Drying Conditions on Physicochemical Properties and Radical Scavenging Ability of Thai Green Tea

The effects of drying conditions using a commercial microwave vacuum dryer on the physicochemical properties and antioxidant activity of Thai green tea were investigated. Nine different drying conditions (power 3200, 3600, and 4000 Watts vs. radiation time 20, 25, and 30 min) were applied in this study. The results showed that individual catechins, their total quantities, radical scavenging ability, and moisture content were significantly affected; however, total polyphenol content and color parameters were not significantly affected by these drying conditions. Based on this data, to obtain optimal physicochemical properties of green tea, drying conditions at 3600 Watts for 30 min were recommended.     

Combined Electrohydrodynamic (EHD) and Vacuum Freeze Drying of Sea Cucumber

A combination of electrohydrodynamic drying (EHD) and vacuum freeze drying (FD) is examined as an improved method for dehydrating sea cucumbers. The energy consumption, shrinkage and rehydration ratio, protein content, and sensory properties, such as the color and trimness, of the dried product in the EHD–FD method are measured. Compared with FD, the combined process consumes less drying time and has lower energy consumption than EHD drying alone. Also, the product processed by combined drying displays lower shrinkage, higher rehydration rate and higher protein content, along with better sensory qualities.     

Energy Analysis of Poly-hydroxybutirate (PHB) Drying Using a Combined Microwave/Rotating Pulsed Fluidized Bed (MW/RPFB) Dryer

The aim of this study was to investigate the drying kinetics and energy efficiency of a combined microwave/rotating pulsed fluidized bed (MW/RPFB) dryer to dry particles of poly-hydroxybutirate (PHB). In order to analyze the effects of microwaves and hot air conditions on the drying kinetics of PHB and energy efficiency, an experimental design technique was applied. Drying energy efficiencies were in the range of 12–30%, and an estimated value of 10.5% was found for pure convective drying of PHB in an RPFB with the same final moisture content.     

Dielectric Properties and Optimization of Parameters for Microwave Drying of Petroleum Coke Using Response Surface Methodology

The dielectric properties of petroleum coke at five temperatures between 20 to 100 ^° C, covering different moisture content levels at 2.45 GHz, were measured using an open-ended coaxial probe dielectric measurement system. The effects of drying temperature, duration of drying, and sample mass on the moisture content and dehydration rate of petroleum coke was assessed utilizing the response surface methodology. The dielectric constant, loss factor, and loss tangent were all found to increase nearly linearly with increase in moisture content. Three predictive empirical models were developed to relate the dielectric constant, loss factor, and loss tangent of petroleum coke as a linear function of moisture content from 3–10%. An increase in temperature between 20 to 100 ^° C was found to increase the dielectric properties. The penetration depth was observed to increase linearly with decrease in moisture content in the range of 3 to 10%. A predictive empirical model was developed to calculate penetration depth for petroleum coke. Two mathematical models were established and analyzed using RSM to describe the relationship between the microwave drying conditions and the responses, moisture content, and dehydration rate. Statistical analysis with response surface regression showed that microwave drying temperature, duration of drying, and sample mass were significantly related to moisture content and dehydration rate. Based on the RSM analysis, the optimum process conditions were estimated to be a microwave drying temperature of 75 ^° C, drying duration of 10 sec, and sample mass of 60 g, with the resultant moisture content being 0.34 at a dehydration rate of 2.94 g/min.     

Effect of Osmotic Pretreatment on Hot Air Drying Kinetics and Quality of Chilean Papaya (Carica pubescens)

The effect of osmotic pretreatment on the mass transfer kinetics and quality of dried rehydrated Chilean papaya was researched. Osmotic treatments were sucrose solutions of 40, 50, and 60% w/w and dried at 60°C; non-pretreated samples were dried at different temperatures (40, 60, and 80°C). Quality parameters were analyzed: proximal composition, rehydration ratio, water-holding capacity, color, vitamin C content, firmness, and microstructure. Non-pretreated samples showed a clear turgor loss, color loss. and low ascorbic acid retention when rehydrated. Osmotic pretreatment improved the quality of rehydrated papayas, showing higher ascorbic acid retention and best firmness and color. Microstructure is better preserved in the pretreated papayas than in the non-pretreated samples, although this difference is minimal.     

Microwave hybrid sintering of 0.95(Mg0.95Zn0.05)TiO3-0.05CaTiO3 ceramics and its microwave dielectric properties

Microwave dielectric ceramic powder of 0.95(Mg_0.95Zn_0.05)TiO₃-0.05CaTiO₃ (MCT) has been prepared by solid-state reaction method through single-step calcination at 1150 °C. The green bodies prepared from the calcined powder have been sintered by conventional, susceptor-aided, and hybrid microwave sintering techniques followed by annealing. XRD of calcined and sintered ceramics show (Mg,Zn)TiO₃ as a major phase with CaTiO₃ as a minor secondary phase. Fractographs of fired ceramics obtained by SEM show similar features in conventional and hybrid microwave types of sintering. Microwave dielectric properties such as relative permittivity(ε_r), temperature coefficient of resonant frequency(τ_f), and unloaded quality factors (Q_u) for conventional sintered at 1325 °C for 4 h are—ε_r~19.8, τ_f< –6 ppm/°C and Q_u.f 69,600 GHz at 6 GHz. Ceramics obtained through susceptor-aided microwave sintering at 1325 °C for 4 h show poor fired density. But ceramics got by microwave-hybrid sintering (resistive + microwave) at the same temperature show ε_r~20.6, Q_u.f~81,600 GHz at 6 GHz and τ_f~?6.9 ppm/°C. The effect of hybrid microwave sintering on the dielectric properties of MCT ceramics is found to be more subtle than microstructural.     

(1-x)Ca_(15/16)Sr_(1/16)TiO_3-xLi_(1/2)Nd_(1/2)TiO_3陶瓷的相组成、显微结构及微波介电性能

采用传统固相法合成了(1-x)Ca_(15/16)Sr_(1/16)TiO_3-xLi_(1/2)Nd_(1/2)TiO_3(CST-LNT)系列微波介质陶瓷材料,研究了该系列材料的物相组成、显微结构及微波介电性能。XRD分析结果表明所有样品均为钙钛矿结构,无二次相出现。随着Li_(1/2)Nd_(1/2)TiO_3的加入,陶瓷平均晶粒尺寸下降,表明Li_(1/2)Nd_(1/2)TiO_3会抑制晶粒生长。随着x的增加,介电常数下降,频率温度系数向负方向移动。当x=0.85时,1250℃保温4 h可以得到优良的微波介电性能:ε_r=125.4,Q×f=2230GHz,τ_f=+14.4 ppm/℃。     

微波辐射作用下La3+,Co2+,Cu2+和Zn2+与Y沸石的离子交换

采用微波辐射法制备了La^3＋/Y、Co^2＋/Y、Cu^2＋/Y和Zn^2＋/Y离子交换型沸石催化剂。通过考察交换原液浓度、加热时间、微波功率等因素对交换度的影响,得出交换反应的适宜工艺条件为：交换原液浓度0.12 mol·L^-1（La^3＋）、0.06 mol·L^-1（Co^2＋）、0.08 mol·L^-1（Cu^2＋）和0.10 mol·L^-1（Zn^2＋）,加热时间6 min（Co^2＋和Zn^2＋）、12 min（La^3＋和Cu^2＋）,微波辐射功率520 W（La^3＋,Co^2＋,Cu^2＋和Zn^2＋）。La^3＋,Co^2＋,Cu^2＋和Zn^2＋与Y沸石的一次交换度分别为80.8%（La^3＋）、69.6%（Zn^2＋）、67.5%（Cu^2＋）和63.8%（Co^2＋）。对比实验结果表明,在相同工艺条件下,微波辐射加热法所需时间仅为传统加热法的1/40～1/80。XRD结果表明,微波辐射对沸石晶体结构无破坏作用。采用“二交二焙”法可使La^3＋与Y沸石的交换度由80.8%提高到91.6%。