Use Of Microwave Pretreatment Research Articles

On the use of microwave pretreatment to assist zero-waste chemical-free production process of nanofibrillated cellulose from lime residue

Microwave (MW) pretreatment as an energy-efficient method to enhance the production of nanofibrillated cellulose (NFC) from lime (Citrus aurantifolia Swingle) residue after juice extraction is proposed. NFC was prepared by subjecting lime residue to MW pretreatment for up to 3 rounds; this was followed by high-shear and high-pressure homogenization. Repeated application of MW pretreatment helped remove non-cellulosic components and resulted in an increased cellulose content and crystallinity index but a decrease in fiber diameter. Freshly prepared NFC sample exhibited gel-like behavior. G′ and G″ of suspension prepared from dried NFC markedly decreased, indicating the loss of gel-like property upon drying. Proper pectin molecular weight as well as pectin content were noted to play an important role in controlling aggregation of NFC during drying and hence water redispersibility of dried NFC. Significant amounts of pectin and limonin could be recovered and utilized as co-products after the first round of MW pretreatment.

Extraction of phenolic principles: value addition through effective sample pretreatment and operational improvement

Edible plants generally green leafy vegetables contain bioactive Phenolics and antioxidant principles which are important in maintaining the oxidative balance of the human body and are used widely as dietary supplements. Optimal extraction of such principles is the need of the hour for the nutraceutical industries. The work presents three innovative sample pretreatment such as providing additional heat to the thimble, use of microwave pretreated sample and pretreatment with acoustic waves. These modifications are intended to improve the working efficiency and output of traditional Soxhlet extraction and make it at par with modern extraction techniques. Extraction of plant phenolics/flavonoids from edible leaves of Amaranthus viridis Linn (Amaranthaceae) and their subsequent HPTLC mapping was used as the performance indicator. Check of nutraceutical and biological integrity upon application of such pretreatment methods was performed. SEM analysis was carried out to get a true inside of the exctraction events occurring internally. Such findings can be helpful for small scale industries who cannot afford costlier modern extraction methods. Four assumptions have been proposed which can be a critical in impriving any extraction method.

Microwave fragmentation of a synthetic alundum-pyrite ore

ABSTRACT In the mining industry, the comminution process is very inefficient in terms of energy utilisation. Numerous research studies have investigated the use of microwave pre-treatment to fracture ore, prior to subsequent unit operations, such as grinding, flotation and leaching, therefore saving on energy consumption. The objective of the present work was to investigate the microwave fragmentation of a synthetic ore with controllable composition and particle size. The synthetic ore was composed of both a hyperactive material (pyrite) and an active material (alundum cement), which were compacted into a briquette. Heating behaviour, permittivity and thermogravimetric/differential thermal analysis (TGA/DTA) studies were conducted in order to understand the fundamental interactions of powdered samples with microwaves. The briquettes were processed in a microwave system followed by compression testing and image analysis to determine the effects of microwaving on the failure load and the fragmentation degree. It was found that the failure load of the briquettes decreased and the fragmentation degree increased with increasing pyrite particle size, pyrite content, and microwave energy absorption.

Microwave Pretreatment for Thiourea Leaching for Gold Concentrate

In this research, we studied the use of microwave pretreatment to enhance the efficiency of Au leaching from gold concentrate. The gold concentrate was pretreated using microwaves with different irradiation time. The sample temperature was increased up to 950 °C by the microwave irradiation. A scanning electron microscope-energy dispersive spectrometer showed the evolution of microcracks and the reduction of sulfur on the mineral surface. X-ray diffraction data also showed the mineral phase shift from pyrite to hematite or pyrrhotite. A leaching test was conducted for the microwave-treated and untreated gold concentrates using thiourea. Although the thiourea leaching recovered 80% of Au from the untreated concentrate, from the treated concentration, the Au could be recovered completely. Au leaching efficiency increased as the microwave irradiation time increased, as well as with a higher composition of thiourea.

Effect of Microwave Treatments on Antioxidant Activity and Antigenicity of Fish Frame Protein Hydrolysates

Protein solubility, protein recovery, antioxidant activity, and antigenicity of microwave pretreatment and/or microwave-assisted hydrolysis of trout frame protein hydrolysates was investigated. Treatments consisted of (1) microwave pretreatment at low temperature (55 °C) followed by conventional enzymatic hydrolysis or (2) high temperature (90 °C) followed by conventional enzymatic hydrolysis; (3) microwave pretreatment at high temperature (90 °C) followed by microwave-assisted enzymatic hydrolysis, and (4) no microwave pretreatment followed by microwave-assisted enzymatic hydrolysis. Compared to controls, microwave treatments significantly improved (P < 0.05) protein solubility, protein recovery, degree of hydrolysis, and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) free radical scavenging radical scavenging activity. Decrease of antigenicity (55–93 %) was obtained in all microwave-treated samples. Based on the results of this study, the use of microwave pretreatment for 5 min at 90 °C, followed by conventional enzymatic hydrolysis with alcalase for 2–10 min was the best treatment condition to produce fish peptides with antioxidant activity and the lowest immunoreactivity. These peptides have potential to be applied as hypoallergenic ingredients in food formulations and nutraceuticals.

Microwave pretreatment can enhance tolerance of wheat seedlings to CdCl 2 stress

In order to determine the role of microwave in cadmium stress tolerance of wheat ( Triticum aestivum L.), seeds were exposed to microwave radiation for 0, 5, 10 and 15 s (wavelength 125 mm, power density 126 mW cm −2, 2450 MHz), and when the seedlings were 7 d old (with one fully expanded leaves), they were treated with 150 μM CdCl 2 solution for 10 d. Changes in a number of physiological and biochemical characteristics were measured and used as indicators of the protective capacity of microwave radiation in this experiment. Our results showed that 150 μM CdCl 2 treatment reduced plant height, root length, dry weight, AsA and GSH concentration and the activities of SOD, POD, CAT and APX, enhanced the concentration of MDA, H 2O 2 and the production rate of O 2 − when compared with the control. However, seeds with microwave pretreatment 5 or 10 s conferred tolerance to cadmium stress in wheat seedlings by decreasing the concentration of MDA and H 2O 2, the production rate of O 2 − and increasing the activities of SOD, POD, CAT, APX and AsA and GSH concentration. Therefore, antioxidative enzymes and antioxidative compounds may participate in tolerance of wheat seedlings to cadmium stress. The results also showed that the microwave radiation had a positive physiological effect on the growth and development of cadmium stressed seedlings. This is the first investigation reporting the use of microwave pretreatment to enhance cadmium stress tolerance of wheat.

Evaluation of energy consumption in different drying methods

This study was conducted to evaluate energy consumption in various drying systems including hot-air convection, use of microwave pretreatment with convection dryer, microwave drying, vacuum drying and infrared drying. Tests were conducted using pomegranate arils under various experimental conditions as follows. In convection dryer at six temperature levels (45, 50, 55, 60, 65 and 70 °C) and three air velocity levels (0.5, 1 and 1.5 m/s) at three pretreatments of control, 100 W microwave pretreatment for 20 min and 200 W microwave pretreatment for 10 min. Experiments in the microwave dryer were done at three power levels of 100, 200 and 300 W and in vacuum dryer at five temperature levels (50, 60, 70, 80, and 90 °C) under 250 kPa pressure. For infrared drying, there were four air velocity levels (0.3, 0.5, 0.7 and 1 m/s) and three illumination levels (0.22, 0.31 and 0.49 W/cm 2). Experimental results showed that minimum and maximum energy consumption in pomegranate drying were associated with microwave and vacuum dryers, respectively. The use of microwave pretreatment in drying pomegranate arils in hot air dryer decreased drying time and energy consumption in comparison with pure convection drying. In infrared drying, it was found that drying time increased with air velocity which resulted in increased energy consumption.

Microwave Treatment of Eight Seconds Protects Cells of lsafis indigofica from Enhanced UV‐8 Radiation Lesions

To determine the role of microwaves in the stress resistance of plants to enhanced ultraviolet-B (UV-B) radiation, Isatis indigotica Fort. seeds were subjected to microwave radiation for 8 s (wavelength 125 mm, power density 1.26 mW mm(-2), 2450 MHz). Afterwards they were cultivated in plastic pots in an artificial-glass greenhouse maintained at 25 degrees C, 70% relative humidity, and 400 micromol mol(-1) CO2, under visible-light conditions of 1500 micromol m(-2) s(-1) for 8 h day(-1). When the seedlings were 10 days old, they were subjected to 10.08 kJ m(-2) UV-B (PAR: 220 micromol m(-2) s(-1)) radiation for 8 days. Changes in a number of physiological and biochemical characteristics and in the thermal decomposition enthalpy of biomass were measured and used as indicators of the protective capacity of microwave radiation in this experiment. Our results revealed that microwave pretreatment of seeds enhanced UV-B stress resistance in the seedlings by decreasing the concentration of malondialdehyde (MDA) and increasing the concentration of ascorbic acid (AsA) and UV-B-absorbing compounds, increasing the activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), and increasing the energy accumulation of photosynthesis. All these results suggest that microwave radiation enhances plant metabolism and results in increased UV-B stress resistance. This is the first investigation reporting the use of microwave pretreatment to protect the cells of Isatis indigotica from UV-B-induced lesions.

Use of microwave pretreatment for enhanced anaerobiosis of secondary sludge

This work elucidates the effects of pretreatment of secondary sludge by microwave irradiation on anaerobic digestion. The soluble chemical oxygen demand (COD) concentration increased up to 22% as microwave irradiation time increased, which indicated the sludge particles disintegrated. Three identical automated bioreactors with working volume of 5 l were used as anaerobic digesters at mesophilic temperature (35 degrees C). The reactors were separately fed with sludge with microwave pretreated- and control- sludge at different hydraulic retention times (HRT). The volatile solid (VS) reduction in the control operation was approximately 23.2 +/- 1.3%, while it was 25.7 +/- 0.8% for the reactors with the pretreated sludge. The average biogas production rate with the pretreated sludge at 8, 10, 12, and 15 days HRTs was 240 +/- 11, 183 +/- 9, 147 +/- 8, and 117 +/- 7 ml/l/d respectively, while those with the control sludge were 134 +/- 12 and 94 +/- 7 ml/l/d at 10 and 15 days HRTs. Maximum rates of COD removal and methane production with the pretreated sludge were 64% and 79% higher than those of the control system, respectively.

Tissue preparation for immunocytochemistry.

AIMS: To investigate the effect of tissue preparation on immunostaining and to establish whether there is a standard tissue preparation schedule that allows optimal demonstration of all antigens. METHODS: Blocks...