Effect Of Microwave Power Level Research Articles

Microwave treatment effect on functional and pasting properties, and storage stability of white finger millet

AbstractMicrowave (MW) treatment is a promising technique in cereal processing to improve nutritional quality. The present study investigated the effect of MW power level and exposure time on white finger millet flour (WFMF). Nine different MW treatment combinations were taken based on power level (720 W, 840 W, and 900 W), and exposure time (2 min, 4 min, and 6 min), after the MW treatment the flours are stored at 45°C for 15 days for storage study. The physicochemical, functional, pasting properties, and storage stability of the treated flours were analyzed. According to the results of the study, MW power level and exposure time significantly (p < 0.05) affected the color, swelling power, and water and oil absorption index. The MW treatment reduces the free fatty acid (FFA) and peak viscosity of the samples. The storage study for up to 15 days reveals the changes in color, FFA, and pasting properties of the sample. During storage, the change in FFA content was higher in control untreated flour (CF) than MW treated samples. Due to the structural changes in the starch molecules, the viscosity of MW treated samples was reduced drastically than the CF sample. Results denote that both MW power level and exposure time had a significant effect to alter the functionality and storage stability of WFMF.Practical ApplicationsWhite finger millet (WFM) is the major raw material used for numerous cereal‐based products. Microwave (MW) treatments are a novel and promising technology used in cereal processing. A study on changes in finger millet properties under MW treatment helps to improve/alter the functional properties of millet flour, which can be used in new product development. Based on the study, MW treatment significantly improves storage stability by reducing the free fatty acid content, so MW treatment can be used to maintain the quality of the WFM during the storage period to minimize storage losses.

The effect of microwave power level and post-synthesis annealing treatment on oxygen-based functional groups present on carbon quantum dots

Despite widespread interest in understanding the properties of carbon quantum dots (CDOTs), there appear to be fewer studies systamaticaly investigating CDOTs' luminescent mechanisms. The primary objective of this study is to prepare CDOTs with desirable optical properties and to understand the photoluminescence (PL) mechanisms involved in order to control the emission charectersitcs. The optical properties of CDOTs are strongly influenced by the functional groups (-OH, –CHO, –COOH, –CO, –COO) formed on the surface of the dots. The key factors affecting the nature and number of functional groups are the preparation method, post synthesis treatment, and the precursor materials. Ascorbic acid was used as the starting material in this study to synthesize CDOTs via microwave-assisted synthesis techniques. Then, the effect of microwave power level and post synthesis annealing temperature on the oxygen-based functional groups present on the surface of the dots was evaluated systematically. It was found that the increasing microwave power level increases the density of functional groups present on the surface of CDOTs, which positively affects the PL. However, annealing at high temperatures decreases the concentration of functional groups and reduces the PL intensity. The PL emission peaks were deconvoluted and the emission wavelength corresponding to each functional group was identified. This work underlines the role of oxygen based functional groups on the PL emission and the ways to control them by physical means.

Microwaved Vermicast Physicochemical Properties and Active Microbial Groups Impact on Photosynthetic Activity, Growth and Yield of Kale

Microwave technology has wide applications, including extraction of active compounds in biomass and compost for agricultural use. A study was carried out to determine the effects of microwave power level from 0 (control) to 1000 W on the properties and active microbial groups in vermicast, and how it may impact the photosynthesis, plant growth, and yield of kale (Brassica oleracea var. sabellica) ‘Red Russian’. Heat accumulation in the vermicast increased rapidly to a peak of 86 °C at 400 W before declining to 68 °C at 1000 W. Vermicast water loss increased exponentially up to 800 W before declining. The C:N ratio of the vermicast was reduced at ≥600 W while the pH remained the same. In a 2D-principal component analysis biplot, vermicast treated at 600, 800 and 1000 W were associated with Gram-positive (G+), GGram-negative (G−), G + G− bacteria, protozoa, and fungi groups while the 0, 200, and 400 W treated vermicast were associated with eukaryotes. However, the trend for total microbial mass was 200 W = 400 W > 0 W > 600 W = 800 W = 1000 W. Kale leaf anthocyanin, chlorophylls, and carotenoids were significantly (p = 0.001) increased by the 400 W or 600 W treatment compared to the other treatments. Stomatal conductance, transpiration, and photosynthesis rates were increased by the 400 W followed by the 600 W. As a result, yield of kale grown in the 400 W microwaved vermicast was the highest. Future studies will explain the functions of specific microbial populations and elemental composition in microwaved vermicast.

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.

Microwave Treatment of Coconut Inflorescence Sap (Kalparasa®): A Panacea to Preserve Quality Attributes

Coconut inflorescence sap, traditionally called as neera, is a natural and healthy drink obtained by tapping the unopened immature spadix of coconut. The sap tapped by using the device coco-sap chiller, developed by ICAR-Central Plantation Crops Research Institute, is called Kalparasa®. The shelf life of the sap after extraction is 2–3 h in atmospheric condition. Farmer producer companies and palm sap processing industries require suitable preservation techniques to maintain the physico-chemical properties of the coconut sap. Hence, the effect of microwave power level (600 and 900 W) and exposure time (30, 60, 90, and 120 s) on the physico-chemical properties of Kalparasa stored under refrigerated conditions was investigated. The physico-chemical properties of microwave-treated Kalparasa including pH, TSS, titratable acidity, ascorbic acid, total sugar, reducing sugar, and polyphenols were analysed at 1, 3, 5, 7, 9, 12, and 16 days after storage. The results reveal that the microwave treatment and storage period had a significant effect (P < 0.001) on the physico-chemical properties of Kalparasa. Furthermore, it was deduced that a combination of high power (900 W) and exposure time (120 s) maintains the physico-chemical quality of Kalparasa up to 16 days of storage under refrigerated conditions.

Evaluation of microwave toasting of corn flakes

During flake production, corn undergoes processes of cooking, drying, tempering, laminating, and toasting. The toasting dictates the attributes of the finished product for the consumer acceptability. Traditionally corn flakes are toasted in high efficiency forced convection systems such as rotary or fluidized-bed ovens. The aim of the present work was to study microwave thin layer toasting of cooked flakes using a household oven. Flakes toasted in a fluidized-bed industrial oven were adopted as control. The effect of microwave power level and process time on the kinetics of dehydration and quality parameters such as bulk density, thickness, and sensorial attributes of flakes were investigated. Kinetics data were satisfactorily simulated by Peleg's equation as function of drying time. A relationship between moisture ratio, output energy, and microwave power was also derived from experimental tests. A significant reduction of processing time in comparison with the traditional method was observed by selecting a suitable level of microwave power. Practical applications This paper describes an innovative and novel method to obtain organoleptically acceptable corn flakes. The results demonstrated that microwave heating can be used to substitute the traditional drying systems used for flakes toasting, with the possibility of reaching a reduction of process time, depending on the accurate selection of process parameters.

Synthesis and characterization of biocoal from Cymbopogon citrates residue using microwave-induced torrefaction

Abstract This study investigates the effects of microwave-induced torrefaction on the characteristics of lemongrass (Cymbopogon citrates) residue. The effects of microwave power level and reaction time on the proximate and elemental contents, surface morphology, surface chemistry, textural properties, thermal stability, higher heating value (HHV), hydrophobicity, and mass and energy yield of the torrefied lemongrass residue were determined. The development of tubular structure on the torrefied lemongrass residue improved its grindability performance. HHV of 19.37 MJ/kg was achieved by lemongrass residue torrefied at 300 °C. The reduction of H/C and O/C ratios were 14.3% and 60.0%, respectively. Mass and energy yield of the torrefied lemongrass residue was 61.20–81.50% and 66.11–83.85%, respectively. The biocoal showed lower moisture absorbing capacity and was less easily to be segregated into fine particles. The enhancement of physicochemical and thermal characteristics of the lemongrass residue proved the feasibility of converting this biomass into biocoal via microwave-induced torrefaction followed by pelletization.

Drying Kinetics of Microwave-Dried Vegetable Amaranth (Amaranthus dubius) Leaves

The effect of microwave power level (200, 500, 700 and 1000W) on the drying behaviour of amaranth (Amaranthus dubius) leaves was investigated. Higher microwave power levels effected faster drying and there was an increase in drying rate constant (k) as microwave power level increased from 200 to 1000W and an increase in diffusivity (Deff) values from 3.04 x 10-10 to 2.82 x 10-9 m2/s. Leaves dried at 1000W power level however showed noticeable scorching after 540s of drying. Drying at the lower microwave power levels occurred in the constant and falling rate period, while at the higher power levels drying occurred in the falling rate period after an initial warm-up phase. Amaranth leaves could be dried at 700W power from an initial moisture content of 6.00 g H2O/g DM (85.7% wb) to 0.08 g H2O/g DM (7.6% wb) in 11.5 min. Overall, of the twenty-two thin layer models applied to the MR data, the Alibas model gave the best fit in terms of both the root mean square error (RMSE) and the chi-square statistic (c2).

Microwave Drying of Black Olive Slices : Effects on Total Phenolic Contents and Colour

In this study, the drying behaviour of black olive slices using microwave was investigated and the effects of microwave power on total phenolic content and colour were determined. Black olive slices were dried at different power levels (180, 360, and 540 W) using a microwave cabin. The results showed that the drying time of the olive slices decreased considerably as the microwave power increased. The total phenolic content of the product dried at 540 W was found to be significantly lower than those dried at 180 or 360 W. For the microwave power range studied, the use of an irreversible first-order model adequately described the decrease in the total phenolic content. The effects of microwave power level on changes of the surface temperatures and weight loss of the olive slices were also determined. The temperature increase and the weight loss were the highest at 540 W during drying. Changes in the colour values (L*, a*, and b*) of the black olive slices during drying were statistically different (P&amp;amp;lt;0.05) for each microwave power level and the maximum change in brightness occurred drying at 360 W. It is thought that results obtained in this study will provide valuable data for the design of microwave drying systems used for drying of olive slices in pilot or industrial scales.

Optimization of microwave-vacuum drying of pomegranate arils

Pomegranate arils (Punica granatum L.) were dried in a microwave-vacuum drier up to a final moisture content of around 5–6 % (d.b.). The effect of microwave power level (25–95 W), vacuum pressure (25–195 mm Hg) and sample mass (65–235 g) on drying efficiency and some quality attributes (color, texture, rehydration ratio and sensory score) of dried pomegranate arils 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 experimented data. All three process parameters microwave power, vacuum pressure and sample mass strongly affected quality attributes of dried pomegranate arils and drying efficiency. A lower vacuum pressure during drying resulted in better quality products. Optimum drying conditions of microwave power level of 80 W, vacuum pressure of 60 mm Hg and sample mass of 193.7 g were established for microwave-vacuum drying of pomegranate arils. Separate validation experiment was conducted at the derived optimum conditions to verify the predictions and adequacy of the models.

Properties of walnut influenced by short time microwave treatment for disinfestation of insect infestation

Insect infestation is the major cause of losses in many stored products such as grains, seeds, cereals and nuts. The use of chemicals to control insect infestation has widely been adopted but now is a cause of concern because of hazardous side effects. Alternative quarantine methods such as ionizing radiation, controlled atmosphere, conventional hot air treatment and dielectric heating have been suggested. Recent studies have indicated that microwave treatment is a potential means of replacing other techniques because of selective heating, absence of pollution in the environment, the achieving of equivalent or better quality retention and energy minimization. However improper application of microwaves can cause irreversible changes in the quality of the final product. The main objective of this research is to evaluate the effect of microwave power level and exposure time on the quality of walnuts. The quality parameters studied were water activity, colour change, temperature rise, peroxide value (PV) and free fatty acid levels (FFA). It was found that microwave power level and exposure time significantly affected colour change and temperature rise. Untreated walnut kernels exhibited significantly higher (p < 0.05) peroxide and FFA values than treated walnut kernels. Microwave treatment to target temperatures of 50–55 °C (which is unfavourable for insect survival) made the PV of walnut drop down to between 1.35 and 1.42 meqO2/Kg (from the initial value of 2.89 ± 0.048) and FFA value to 0.63–0.69% (from 1.08 ± 0.037).

MAE of phenolic compounds from blueberry leaves and comparison with other extraction methods

Blueberry leaves are a prospective source of phenolic compounds which can be obtained by microwave assisted extraction leading to higher yield in shorter period of time and with lower solvent consumption when compared to solvent extraction. During this study, three experiments with microwave assisted extraction, were separately designed and conducted using highbush blueberry (variety Bluetta) leaves collected during the late fall season. The yields of different compounds obtained during these experiments with microwave extraction were compared with ultrasonic extraction for one hour and 24-h room temperature extraction. The first microwave assisted extraction experiment was conducted to streamline the combination of ethanol and citric acid concentration for further analysis of microwave as a potential extraction method for phenolic compounds and anthocyanins from blueberry leaves. During the second experiment the effect of microwave power level (10–20% absolute power level) and time of extraction (4–16min) on total phenolics, total anthocyanins and chlorogenic acid was studied which was further used to design the third experiment consisting of a face-centred central composite design with varying factors namely power level and time, each at 3 levels. All the experimental combinations for the 2nd and 3rd experiments were conducted with 80ml of solvent consisting of 30% ethanol and 1.5M citric acid combination in ratio of 97:3 (v/v). The total anthocyanins and chlorogenic acid extracted during the study were between 2.321–2.636mg malvidin 3-glucoside/g dry matter and 49.34–52.66mg chlorogenic acid/g dry matter respectively, not showing a huge variation between highest and lowest yields, however both compounds with a noteworthy yield. For total phenolics extraction, both microwave power and time of microwave application were observed to be statistically significant factors and the yield of total phenolics was found to be much higher (in the range of 92.719–128.76mg GAE/g dry weight) than for 24-h extraction at room temperature (average 89.164mg GAE/g dry weight) and 1h extraction by sonication (average 97.77mg GAE/g dry weight) with the same solvent combination.

Experimental Research on Tensile Strength Reduction of Concrete Caused by Microwave Irradiation

In order to understand the law on concrete degradation induced by microwave irradiation, the experimental research is conducted in which the following works are completed. At first, the different concrete specimens are exposed to microwave of various power levels for various time periods, and then some specimen irradiated by microwave are cooled in air, the other cooled by spraying water. After that, the tensile strengths of the heated and unheated specimens are measured with Brazilian test method. According to the test results, the reduction of tensile strength of plain concrete and steel-fiber reinforced concrete induced by microwave irradiation is analyzed, and the relations between the tensile strength reduction and the microwave exposure time and the effect of microwave power level on the residual tensile strength of concrete are obtained. The experimental research shows that the tensile strength reduction of concrete induced by microwave irradiation is dependent on the concrete component, microwave exposure time, microwave power level, and cooling method after irradiation. It is expected that the findings in the paper will become the basis of the future research of concrete and rock degradation induced by microwave irradiation, and will aim in searching the new method of breaking concrete and rock more efficiently.

Preparation and characterization of activated carbon from leather waste microwave-induced pyrophosphoric acid activation

The present study probes the preparation of activated carbon using pyrophosphoric acid (H4P2O7) as the activating agent by microwave heating from leather waste (LW). The effect of microwave power level and radiation time on BET surface area and carbon yield of activated carbon (AC) was discussed. The properties of AC were characterized by thermogravimetric analyses (TGA), the element analyzer, scanning electron microscopy (SEM) and Fourier transforms infrared spectroscopy (FTIR). Methylene blue (MB) was chosen as model dye compound to evaluate the adsorption behavior. The best conditions for preparing activated carbon were identified to be: microwave power level of 700W and radiation time of 15min with BET surface area of 638.57m2/g and carbon yield of 36.25%. Equilibrium data were better fitted by the Langmuir isotherm model, indicating a monolayer adsorption capacity of 303.03mg/g.

Microwave drying and moisture diffusivity of white mulberry: experimental and mathematical modeling

The literature surveyed revealed that drying kinetics of white mulberry under microwave treatment has not been investigated. In present study, both experimental study and mathematical modeling on microwave drying of white mulberry was performed. The microwave drying process which reduced the moisture content of mulberry from 3.76 to 0.25 (g water/g dry matter) was carried out at 90, 180, 360, 600, and 800 W in a modified microwave drying set-up. The effects of microwave drying technique on the moisture ratio and drying rate of white mulberry were investigated experimentally. Both the effects of microwave power level (under the range of 90–800W) and initial sample weight (50–150g) were studied. No constant rate period was observed. Mathematical modeling of thin layer drying kinetics of white mulberry under microwave treatment was also investigated by fitting the experimental drying data to eight thin layer drying models. Among the models proposed, Midilli et al. model precisely represented the microwave drying behavior of white mulberry with the coefficient of determination higher than 0.999 and mean square of deviation (χ2) and root mean square error (RMSE) lower than 1.1×10−4 and 8.9×10−3, respectively for all the microwave drying conditions studied. The effective moisture diffusivity (Deff) of white mulberry varied from 0.45×10−8 to 3.25×10−8 m2s−1. Both the drying constant (k) and Deff increased with the increase of microwave power level.

Microwave-Assisted Thin Layer Drying of Wheat

Drying characteristics of Canada Western Red Spring (CWRS) wheat were studied using a domestic microwave convective oven. The effects of microwave power level, grain bed thickness, and initial grain moisture on the drying kinetics were investigated. Wheat samples with initial moisture levels of 0.18 to 0.29 kg water/kg of dry matter were dried for different drying periods of 180 to 360 s. The moisture loss data were recorded at regular short intervals. Then moisture loss data were fitted to various models (Page equation, modified drying equation, and Midilli equation) to study the drying kinetics of wheat. The results showed that wheat moisture loss increased with increasing microwave power level. A mathematical model was developed by coupling mass and energy balances, resulting in a system of non-linear equations. The predicted moisture loss data from the developed model were compared by fitting to experimental microwave data that were in good agreement.

Investigation on the drying kinetics of sliced and whole rosehips at different moisture contents under microwave treatment

Microwave drying kinetics of rosehips (Rosa Canina L.) harvested at different moisture contents was investigated. The experiments were conducted for both sliced and whole rosehips at different microwave power outputs (90 to 800 W) in a modified microwave drying set-up. Rosehips with initial moisture contents of 0.44 to 0.80 (g water/g dry matter) were dried to moisture content lower than 0.1 (g water/g dry matter). The effects of microwave power level, initial moisture content and slicing on moisture content and drying rate were studied. Drying took place in the falling rate period. To determine the kinetic parameters, drying data were fitted to ten mathematical thin layer drying models. Among the models proposed, Page model precisely represented the microwave drying behavior of rosehip with the coefficient of determination higher than 0.997 and mean square of deviation and root mean square error lower than 4.7×10-4 and 17 ×10-3, respectively for all output powers studied. Values of drying constant (k) were in the range of 0.0049 to 0.23 min-1. Key words: Drying kinetics, microwave drying, thin layer drying models, rosehip.

전자레인지 출력에 따른 분쇄 돈육 패티의 가열패턴 및 품질특성

This study was carried out to evaluate the effects of microwave power level on cooking properties of ground pork patties (fat level: 20%). Each patty was cooked from a thawed state to <TEX>$76.7^{\circ}C$</TEX> (center temperature) in a microwave oven with power levels of 40% (360 W), 60% (540 W), 80% (720 W), and 100% (full power, 900 W), respectively. Cooking rate increased with power level, and the non-uniformity also increased with time during cooking. Overheating at the edge of the patties was observed for all power levels, and maximum temperature differences in between the edge position and center position were found in patties cooked at the 900 W power level. Compositional properties, total cooking loss, and drip loss were not affected by power level, although moisture content was lower at the edge than at the center position. As the power level increased, the reduction in patty diameter of cooked patties increased while the reduction in patty thickness decreased. Pork patties cooked at lower power levels (360 W and 540 W) had higher shear force values than those cooked at higher power levels (720 W and 900 W). Few changes were observed in instrumental color values.

The Role of Processing Parameters on Energy Efficiency during Microwave Convective Drying of Porous Materials

A small-scale microwave convective dryer was built to study the effects of microwave power level, air temperature, and air velocity on drying kinetics, temperature development, and specific energy consumption (MJ/kg evaporated water) using statistical designs. Increased microwave power had a large significant effect on moisture loss and temperature development and it reduced specific energy consumption. Increased air temperature and air velocity increased specific energy consumption, as their effect on drying kinetics was smaller in the system used. Low air temperature slowed the drying process, without affecting the relationship between average sample temperature and average moisture content during drying.

Kinetics of mass transfer in microwave precooked and deep-fat fried chicken nuggets

The objective of this study was to evaluate the effect of microwave precooking on mass transfer during deep-fat frying of chicken nuggets. The effect of microwave power level, frying temperature and time on mass transfer in the breading coating and the core parts were determined. The results showed an interaction effect of these processing conditions on mass transfer. The most reduction in fat absorption was observed when samples were precooked at 6.7 W/g and fried 170 °C. The first order kinetic model fitted the moisture and fat transfer data well except for fat transfer in the core portion. The effective moisture diffusivity for the breading coating and core portion ranged between 6.39 × 10 −10 to 14.7 × 10 −10 m 2 /s and 1.77 × 10 −10 to 14.0 × 10 −10 m 2 /s, respectively, and the R 2 values were between 0.86 and 0.99. Fat transfer rate constant in the breading region was between 0.04 and 40.96 s −1 with R 2 from 0.67 to 0.97. Activation energy obtained from the Arrhenius plot for the effective moisture diffusivity ranged between 13.65 and 54.93 kJ/mol.