Microwave Power Levels Research Articles

Physicochemical characteristics of sweet corn kernels during microwave blanching

Sweet corn kernels are easily perishable because of their high amount of moisture content. Microwave blanching was applied at the power level of 180–900 W for 30–70 s to inactivate the enzymes of sweet corn kernels. The increase in microwave power level and processing time reduced the length from 11.13 to 10.78 mm, width from 9.54 to 9.24 mm, thickness from 4.01 to 3.71 mm, true density from 1052.07 to 1012.03 kg/m3, porosity from 37.43 to 24.54%, moisture content from 70.00% to 68.93% on a wet basis, total soluble solid from 22.3 to 18.7 °Brix, total sugar from 8.80% to 6.67%, ascorbic acid from 8.04 to 5.92 mg/100 g, and peroxidase activity up to 1.37% in sweet corn kernels, but it increased the bulk density from 658.23 to 763.6 kg/m3 and total color difference up to 14.55. Novelty impact statement The microwave blanching was found adequate for processing sweet corn kernels at the power level of 720 W for a short duration of 40 s to achieve a 90% reduction in peroxidase activity. The ascorbic acid, total sugar, overall acceptability after the microwave blanching were 6.86 mg/100 g, 7.87%, and 8.21, respectively, indicating 85, 89, and 94% retention of fresh samples properties. The total plate count was 9.1 log cfu/g in fresh kernels, which was also reduced to 1.8 log cfu/g in kernels blanched at the power level of 720 W for 40 s duration.

Assessment of microwave pretreatment on kinetic modeling of moisture loss and oil uptake and acrylamide constitution during deep frying of carrot slices

The effect of microwave power levels, frying time, and temperature on mass transfer and acrylamide formation during deep-fat frying of carrot slices was determined. Maximum and minimum moisture loss were measured, respectively, in control samples fried at 170°C for 4 min and samples pretreated with microwave at 7 W/g power and fried at 150°C for 2 min. The highest (0.69 g/g) and lowest (0.42 g/g) oil uptake were observed in control samples fried at 150°C for 4 min and samples pretreated with microwave at 7 W/g power and fried at 150°C for 2 min, respectively. The effective moisture diffusion and activation energy ranged from 4.84 × 10−10 to 15.41 × 10−10 m2/s and from 6.47 to 11.75 kJ/mol, respectively. The highest (19.83 µg/kg) and the lowest (<4.67 µg/kg) amount of acrylamide formation were, respectively, measured in control and in microwave pretreated samples (with 7 W/g power for 3 min and fried at 150°C for 2 min). Novelty impact statement Using microwaves as a pretreatment could significantly reduce oil uptake and acrylamide formation in carrot samples. A reduction in acrylamide was observed in this study after increasing the microwave thermal power from 3 to 7 W/g. Some studies have shown that the acrylamide content increases by increasing the thermal power of the microwave. This study reports that the acrylamide content is a function of the processing time, and the increasing thermal power of the microwave reduces the acrylamide content in short processes.

Optimization of Parameters Affecting Noodle Drying by Taguchi Method

In this research, Taguchi method application studies have been carried out to optimize the parameters affecting the drying of noodles made in Çankırı region by sun, conventional oven, and microwave method. In the experimental study, the noodles were dried in a single row in thin strips of 3-4 mm constant thickness to form an area of 100 cm2 (square plate). Variable parameters in three different drying methods are temperature, duration, and microwave power level. Sun drying of noodles was performed at an average temperature of 19 °C in June. Oven drying experiments were carried out at different temperatures (75 °C, 100 °C, 150 °C) and times (30, 60, 90 minutes). Microwave drying operations were performed at 300 W, 450 W, 600W power and 1, 2, 3 minutes respectively. The factors affecting the moisture content that can be separated from the noodles in the conventional oven were determined as drying temperature and drying time. In microwave drying, power and drying time were chosen as control factors. For this purpose, the L9 orthogonal sequence was arranged in Taguchi design used in experimental studies. The effects of control factors were determined by analyzing variance analysis (ANOVA) at 95-97.6 % confidence level. The study also analyzed moisture, ash, protein, color, and volume increase for dried noodles with 3 different drying techniques. In the sun drying of the noodles, 9.47 moisture, 1.33 ash, 10.73 protein, 87.48 L* color value, 1.03 â* color value, 22.46 B* color value, and 282.67 volume increase values were found. In the oven drying, 9.20 moisture, 1.31 ash, 10.77 protein, 80.24 L* color value, 1.64 â* color value, 24.10 B* color value, and 250.23 volume increase values were measured. 8.73 moisture, 1.29 ash, 10.83 protein, 78.50 L* color value, 0.90 â* color value, 25.13 B* color value, and 262.40 volume increase values were determined in the microwave drying.

Microwave-assisted pre-milling treatments of chickpea (Cicer Arietinum) for higher recovery

This research was undertaken to examine the result of microwave pre-treatment on chickpea dehulling. The experiments were conducted at three microwave power levels (PL), 50, 70, and 90, at different five exposers from 1 to 3 minutes at the time interval of 30 seconds to evaluate chickpea dehulling with the pre-milling treatment of microwave exposure for achieving maximum dehulling yield, dhal yield, good dehulled grains in terms of quality with minimum dehulling loss. It was noted that dehulling yield improved with microwave power and exposure period. The highest dehulling yield, 71.02%, was achieved 90 PL with 2.5 minutes exposure and found maximum dhal yields, i.e., 66.40%, and minimum dehulling loss, 10.25%. So, this requirement was correct and better to get a higher dhal yield. These findings are also valuable for the pulse processing industry and fabricators for designing a continuous type pulse pre-milling treater unit. Hence, it could be highlighted that the microwave pre-milling treatment is more suitable for pulse processing like chickpea. This also presents an improvised method for pre-milling treatments for commercial adoption.&#x0D;

Drying kinetics and effective moisture diffusivity of pomelo albedo under vacuum‐assisted microwave drying and its semi‐product

AbstractThe five different microwave power levels (800, 640, 480, 320, and 160 W) assisted with the vacuum of 40 kPa were investigated for the drying kinetics, effective moisture diffusivity and rehydration ratio of the dried pomelo albedo. The comparison of some product quality indicators after production and 6 months of storage was also taken place in this study. The higher microwave power levels provided the shorter drying times, the higher moisture diffusion and the drying rates. Drying time at 160 W needed more than 120 min while the rest needed less than 25 min to reach the moisture content below 8% (dry basis). By basing on χ2 and root mean square error and R2, experimental drying data were best performed for the Page equations compared to other eight models (Diffusion approach, Two term exp, Henderson and Pabis, Lewis, Logarithmic, Vermar, Two modified compartment, Wang and Singh). The effective moisture diffusivity coefficient determined by Fick's second law was varied from 1.0 × 10−5 to 6.52 × 10−7 m2/s. The developed models describing the relationship between different drying parameters in this study can be used for optimizing the parameters in the drying process at a larger scale. The microwave power level of 480 or 640 W and the sample weight of 50 g were recommended for the drying of the pomelo albedo. Under these conditions, the dried albedo product possesses high quality. Most of the characteristic quality indicators changed insignificantly as compared after production and stored for 6 months at room temperature (25–28°C).Practical ApplicationsThe albedo layer consists of cellulose, hemicellulose and pectin which can be used as an ingredient in many foods. Microwave vacuum drying in food processing offers several advantages rather than microwave drying and other traditional drying methods. The combination results in a rapid drying rate, which is one of the desired characteristics for rehydrated products. This combined dying technology becomes well‐known nowadays, which can promise in use at the commercial level in product quality.

Interaction between plasma and electromagnetic field in ion source of 10 cm ECR ion thruster

Through diagnosing the plasma density and calculating the intensity of microwave electric field, four 10 cm electron cyclotron resonance (ECR) ion sources with different magnetic field structures are studied to reveal the inside interaction between the plasma, magnetic field and microwave electric field. From the diagnosing result it can be found that the plasma density distribution is controlled by the plasma generation and electron loss volumes associated with the magnetic field and microwave power level. Based on the cold plasma hypothesis and diagnosing result, the microwave electric field intensity distribution in the plasma is calculated. The result shows that the plasma will significantly change the distribution of the microwave electric field intensity to form a bow shape. From the boundary region of the shape to the center, the electric field intensity varies from higher to lower and the diagnosed density inversely changes. If the bow and its inside lower electric field intensity region are close to the screen grid, the performance of ion beam extracting will be better. The study can provide useful information for the creating of 10 cm ECR ion source and understanding its mechanism.

Bioprospecting microwave-alkaline hydrolysate cocktail of defatted soybean meal and jackfruit peel biomass as carrier additive of molasses-alginate-bead biofertilizer

The extraction of soluble hydrolysate protein and sugar from a biomass cocktail of defatted soybean meal (DSM) and jackfruit peel (JP) was examined using microwave-alkaline hydrolysis by varying the NaOH concentrations (0.04–0.11 M) and residence times (2–11 min). Based on the central composite design, the optimized parameters were achieved at 0.084 M NaOH concentration (100 mL), for 8.7 min at 300 W microwave power level to obtain the highest protein (5.31 mg/mL) and sugar concentrations (8.07 mg/mL) with > 75% recovery. Both raw and detoxified hydrolysate (using activated carbon) were correspondingly biocompatible with Enterobacter hormaechei strain 40a (P > 0.05) resulting in maximal cell counts of > 10 log CFU/mL. The optimized hydrolysate was prepared as an additive in molasses-alginate bead encapsulation of strain 40a. Further evaluation on phosphate and potassium solubilization performance of the encapsulated strain 40a exhibited comparable results with those of free cell counterpart (P > 0.05). The DSM-JP hydrolysate cocktail holds potential as a carrier additive of encapsulated-cell bead biofertilizers in order to sustain bacterial cell quality and consequently improve crop growth and productivity.

Energy consumption and dehydration parameters of microwave drying of carrot

The parameters of microwave dehydration (thickness, mass load, and microwave power level) of carrot slices had a statistically significant (P &lt; 0.05) effect on the drying process. Carrot slices (thicknesses of 3, 6, and 9 mm) were dehydrated as monolayers at microwave power levels (80, 240 W) at different mass loads (1.00, 0.63, and 0.38 kg m-2). The optimal microwave model for the carrot slice microwave dehydration was the model with the microwave power level of 240 W, mass load of 0.38 kg m-2 , and 3 mm thickness, with the shortest dehydration time (15 ± 1 minute) and the lowest energy consumption (0.099 ± 0.002 kWh). The minimum resistance to mass transfer (effective moisture diffusivity) was observed in the models with the thickness of 3 mm, a 1.00 kg m-2 mass load, dehydrated at 80 W (8.2519 × 10-8 ± 8.8815 × 10-10 m 2 s-1). The average activation energy for the analyzed models was 8.972 ± 0.009 W g-1. Therefore, the application of the microwave dehydration method can be considered a proper alternative for the dehydration of carrot slices.

Microwave assisted drying and extraction technique; kinetic modelling, energy consumption and influence on antioxidant compounds of fenugreek leaves

Fenugreek leaves contains bioactive compounds, which are helpful in maintaining human health. These compounds are adversely affected in conventional drying methods. Therefore, this study was carried out to retain maximum amount of these components through microwave-assisted drying and extraction technique. The technique was optimized for simultaneous drying and extraction process for fenugreek leaves. The drying rate and drying time were influenced by the level of microwave power; time was reduced from 21 to 5 minutes, when microwave power was changed from 30 to 100 W. Unlikely, the drying rate increased from 1.79 to 4.56 ± 0.05 g/(100 g.min) with the change in power (30 to 100 W). Moreover, moisture ratio analysis determined that two term model was the best to demonstrate the fitness with experimental values. The energy consumption was lowest for 100W compared to other powers. Furthermore, comparison between microwave-based extraction and methanol-extraction indicated that the antioxidant activity was better preserved compared to conventional ones even at higher microwave power levels.

Microwave-assisted extraction and content determination of astilbin in Lysiphyllum strychnifolium stems

Lysiphyllum strychnifolium (Craib) A. Schmitz. (in Thai name, Ya nang daeng) has been traditionally used to treat fever, alcohol intoxication, cancer, allergies, and blood toxins. It can be used as a health-promoting herbal tea and contains hydroalcoholic extracts. The purpose of the present study was to develop a microwave-assisted extraction method for astilbin in L. strychnifolium stems. HPLC was used to determine astilbin content. Three extraction conditions were optimized: types of solvent, microwave power levels, and the number of extraction cycles. Water:methanol (40:60) was the best solvent for astilbin extraction from L. strychnifolium stems using 450 watts and six microwave-assisted extraction cycles. This technique offers important advantages over conventional methods, such as shorter extraction times, substantial energy savings, and a reduced environmental burden.

Characterizing thermal damage of diorite treated by an open-ended microwave antenna

The thermal damage induced by microwave treatment in rocks has not been well explored, especially when using the dielectric-loaded converging waveguide antennas (DLCWAs). In this paper, the effects of microwave power level, heating time and working distance on the temperature increase, ultrasonic wave velocity reduction, and more importantly, the fracturing characteristics and the damage zone, are comprehensively investigated using a 6 kW microwave source and a customized DLCWA. A novel method is also proposed to adjust the P-wave velocity (Vp) reduction across the thickness of the specimens and to determine the equivalent damage zone. The results show that the temperature and high temperature area, crack number, length and density, and the Vp reduction rate as well as the damage zone all increase as either the power level or the heating time increases and decrease as the working distance increases. The damage zone can be divided into the crushed zone, fracture zone and discrete fragment zone based on the crack characteristics and the crack generation mechanisms. The method proposed is demonstrated to be reliable in predicting the damage zone induced by microwave heating.

DRYING OF ZUCCHINI AND CARROT SLICES: INFLUENCE OF TISSUE STRUCTURE ON MASS TRANSFER PARAMETERS

The present work aimed mainly at investigating the influence of tissue structure on dehydration characteristics of zucchini and carrot. Microwave power levels of 100, 350, 550 and 750 W used to dehydrate the samples with thicknesses of 3, 5, 7 and 9 mm. The results showed that moisture removal from the slices occurred in a short accelerating period at the process beginning followed by a falling rate period. The moisture diffusivity increased with both increasing microwave power and the samples thickness where the average values for zucchini and carrot slices changed from 1.17×10-8 to 9.42×10-8 and from 0.73×10-8 to 5.51×10-8 m2 s-1, respectively. The average activation energy for zucchini and carrot slices varied in the range of 1.22–1.68 and 1.57–1.84 W g-1, respectively and decreased with increasing samples thickness.

Extraction of palm fatty acids from sterilized oil palm mesocarp by microwave technique: Optimization and kinetics

Production of crude palm oil (CPO) from palm oil mill involves several processes such as sterilization, stripping, digesting, and pressing, all of which require great amount of water. Wastewater from these processes is collected in several ponds to produce palm oil mill effluent (POME). They are the main contributor of pollution in the industry and numerous researches have been carried out to reduce the production of POME. One of the methods used to extract oil palm mesocarp is microwave, as it has the advantage of short processing time. Microwave has also been used in the sterilization of oil palm fresh fruit and drying process. To date, limited studies have been conducted in the extraction of oil palm mesocarp by using microwave. Hence, this work investigates the best process conditions extraction of oil palm mesocarp and its kinetic and mathematical model based on heat transfer in the microwave. Temperature increment rate in the microwave was measured by determining the slope of linear regression equation obtained from its temperature profile. Steep slope describes how fast the extraction process occurs. A Box-Behnken design was applied to evaluate the effects of three independent variables of microwave power level (100–400 W), extraction time (20–30 min), and mass of mesocarp loading (80–120 g) on the responses, such as CPO yield and free fatty acids. The optimal extraction condition was found to be at 300 W, 30 min, and 80 g. From this result, based on the kinetics modeling done, it is found that a second-order kinetic model represents the palm fatty acid extraction by microwave-assisted extraction method.

Effect of intermittent microwave drying on nutritional quality and drying characteristics of persimmon slices

The novelty of this paper was to evaluation the effect of intermittent microwave drying (IMD) on the nutritional quality and drying characteristics of persimmon slices. Persimmon slices were treated with IMD at the microwave power levels of 280, 350, 420, 490, and 560 W, and the drying characteristics, nutritional components, and sensory properties were determined and analyzed. The results showed that the drying process of persimmon slices could be divided into three stages; increasing speed, constant speed, and decreasing speed. Meanwhile, the higher the microwave power, the shorter the drying time and the higher the drying rate. With the increase of microwave power, the contents of soluble sugar, soluble tannin, vitamin C, and ash increased gradually, but had no obvious effect on the content of insoluble tannin, while the contents of soluble protein and vitamin E decreased gradually, and the overall acceptability score increased first and then decreased. In this study, the comprehensive scoring method was used for dried persimmon slices. The optimal microwave power for IMD persimmon slices was determined to be 490 W, which could effectively improve the drying rate and nutritional value, and has good sensory acceptability.

Microwave and ultrasound assisted extraction of phytocompounds from black jamun pulp: Kinetic and thermodynamics characteristics

The present study focuses on the extraction of phenolic compounds, anthocyanin and antioxidants from black jamun pulp by microwave and ultrasound assisted extraction process. The microwave-assisted extraction was carried out for 240 s at microwave power level of 100–400 W. The yield of total anthocyanin and total phenolic content in the microwave assisted extraction process at 400 W power level after an extraction period of 240 s was 8.197 mg of C3G g−1 and 37.671 40.632 mg GAE g−1, respectively. The ultrasound assisted extraction was performed at temperatures of 40, 50, 60, and 70 °C for 150 min. In the ultrasound assisted extraction at a sonication temperature of 70 °C, the yield of anthocyanin was 8.525 mg of C3G g−1, while the yield of the phenolic compound was 47.331 mg GAE g−1. The pseudo-second order model was found to be the most suitable model to represent the extraction kinetics of anthocyanin, phenolic compounds, and antioxidant activity of black jamun pulp. The effective diffusion coefficient for ultrasound assisted extraction of phenolic components, anthocyanin, and antioxidant activity in the temperature range of 40-70 °C was 5.704× 10−12–10.515 10−12, 2.485× 10−12 -8.507× 10−12, and 2.061× 10−12–11.977 × 10−12 m2.s−1 respectively. The negative Gibbs free energy change values for extraction of phenolic compounds and anthocyanin specified that the reaction was feasible and spontaneous. Thermodynamic parameters such as positive enthalpy change and positive entropy change indicated that the ultrasound assisted extraction process was endothermic and irreversible in nature.

Comparison of Microwave-Assisted Extraction to Soxhlet Extraction of Mango Seed Kernel Oil using Ethanol and n-Hexane as Solvents

Mango seed kernel oil was extracted by Soxhlet Extraction (SE) and Microwave-Assisted Extraction (MAE) with ethanol and n-hexane as extraction solvents. To optimize the extraction condition for SE, the temperature was set to 90°C for ethanol and 80°C for n-hexane with varying solvent-to-feed ratios (S/F ratio) of 75/12, 75/10, and 60/6 mL/g. As for MAE, the same S/F ratios were considered. Extraction was done for 5, 10, and 15 minutes with microwave power levels of 120 and 240 W. It was found out that the highest yield per extraction process for SE was: 18.00±0.25 % and 9.38±2.03 % using ethanol and n-hexane, respectively; and 6.69±0.05 % and 4.68±0.06 %using ethanol and n-hexane, respectively for MAE. It was also noted that MAE, with the microwave power level of 120 W has less extraction time for about 15 minutes as compared to SE of 8 hours. Also, the best S/F ratio in this study is 60/6 for all processes. In oil quality determination, the oil extracted was examined through several tests such as FTIR, GC-MS, acid value, % FFA, iodine value, saponification value, and melting point. It was noted that oil extracted in ethanol has a better yield compared to that of n-hexane but the oil extracted using n-hexane would provide superior quality.

Effect of different microwave power levels on inactivation of PPO and PME and also on quality changes of peach puree

The effect of microwave (MW) treatment with different power densities (4.4, 7.7, and 11.0 W/g) on polyphenol oxidase (PPO) and pectin methyl esterase (PME) inactivation in peach puree were studied, and the changes in color, rheological properties, total polyphenol and flavonoid and antioxidant capacity were evaluated. By using time/temperature data collected during MW heating, three cook values levels (0.36, 10, 24 min) for each power density were calculated. The PPO was significantly decreased from ca. 50% to ca. 5% when increasing the cook value level, regardless of power density applied. While PME significantly decreased from 40.6% to 10.2% when power density increased from 4.4 to 11.0 W/g at cook value 24 min. MW treatment did not alter the flow behaviour of peach puree. The apparent viscosity values of peach puree significantly increased after MW treatment with increasing cook value, regardless of power density applied. The L* values of peach puree significantly increased from 36.98 to 38.10 or more after MW treatment at cook value 10 min and 24 min. MW treatment could maintain the amount of total polyphenol, total flavonoid and antioxidant capacity, preserving the nutritional and functional values of the product.

Central composite design, Pareto analysis, and artificial neural network for modeling of microwave processing parameters for tender coconut water

Polyphenol oxidases (PPO) and peroxidases (POD) are the major enzymes that affect the quality of tender coconut water (TCW). Advanced thermal treatment such as microwave treatment has the potential for the inactivation of food enzymes. The experiments were conducted at three different microwave power levels (450, 600, and 900 W) and five different exposure times (70, 80, 90, 100, 110, and 120 s). The modeling and optimization of process parameters were done using a central composite design and artificial neural network. The microwave power level of 600 W for 120 s exposure time was suitable for enzyme inactivation with minimal quality loss. Optimized treatment has pH=5.02, total soluble solids (TSS)=5.68 °Brix, turbidity=12.51 NTU, titratable acid (TA)=0.07% of malic acid, PPO=0, POD=0, phenolic content=37.238 mg GAE/L and overall acceptability (OA)=7.5. These results confirmed that microwave treatment could be the potential alternative to conventional thermal treatment for processing tender coconut water.

Effect of microwave treatment on the thermal properties and dynamic splitting behavior of red sandstone

Microwave energy is a promising application in future rock breakage operations in the civil, mining, processing, and space industries. Rock engineering projects frequently experience mechanical vibration and blasting impacts. Thus, understanding the dynamic fracturing behavior of microwave-treated rock is essential for its future application in microwave-assisted mechanical rock breakage. A customized industrial microwave system with a multimode resonant cavity was used to heat red sandstone at different microwave power levels (up to 4 kW) for a constant exposure time (4 min). The rock surface temperature distribution after microwave treatment was measured by an infrared camera. Dynamic splitting tests were conducted using a split Hopkinson pressure bar (SHPB) system in combination with a high-speed camera. Experimental results indicate that the rock dynamic splitting strength is negatively related to the microwave power, and the maximum reduction is 47.8%. Microwave treatment induced an obvious nonuniform temperature distribution and C-shaped surface cracks on disc specimens. During the dynamic splitting test, the crack induced by dynamic loading always initiates from the crack tip induced by microwave irradiation and then propagates along the loading diameter. The distribution of the inner high-temperature zone in the disc specimen is symmetric along the horizontal centerline of the disc specimen.

Inactivation of Salmonella spp., Escherichia coli O157:H7 and Listeria monocytogenes in Tahini by Microwave Heating.

Tahini (sesame paste) is a traditional food. Numerous foodborne outbreaks have been associated with it. This study aimed to (i) explore the efficiency of 2450 MHz microwave heating at 220, 330, 440, 550, and 660 W on the inactivation of Salmonella spp, Escherichia coli O157:H7, and Listeria monocytogenes in tahini; (ii) determine the impact of desiccation and starvation stresses on pathogen survival; (iii) assess the impact of microwave heating on the physicochemical characteristics of tahini. The inoculated microorganisms in tahini were reduced with higher microwave power levels (p < 0.05) and longer exposure times. The D-values of unstressed Salmonella spp., Escherichia coli O157:H7, and L. monocytogenes ranged from 6.18 to 0.50 min, 6.08 to 0.50 min, and 4.69 to 0.48 min, respectively, at power levels of 220 to 660 W, with z-values of 410, 440, and 460 W, respectively. Generally, desiccation and starvation stress levels prior to heating increased microbial resistance to heat treatment. Microwave heating did not affect acid, peroxide, p-anisidine, or color values of tahini up to 90 °C. These findings reveal microwave heating as a potential method for lowering the risk of Salmonella spp., E. coli O157:H7 and L. monocytogenes in tahini with no compromise on quality.