Microwave-assisted Extraction System Research Articles

Studying the Optimization, Characterization, and Antioxidant Activities of Phenolic Extracts Extracted from Rhus chinensis Mill. Leaf using Microwave-assisted Extraction System with Glycerol as a Green Solvent

Background: The leaves of Rhus chinensis Mill., a common deciduous tree found in the mild temperate zone of Asia, have many medicinal effects, including antioxidant properties. Objectives and Methods: This study aims to optimize the conditions for extracting phenols from Rhus chinensis Mill. (RCM) using a microwave-assisted extraction system with glycerol (MAEG) via response surface methodology (RSM). It also aims to compare the extraction efficacy of decoction and MAEG methods in terms of the bioactive compounds and antioxidant activities of the extracts obtained through them, identify bioactive compounds in both extracts via ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-ESI-QTOFMS/ MS), and determine the cytotoxicity and cellular antioxidant activity of MAEG extract. Results: Temperature and glycerol concentration significantly affected the total phenolic content (TPC) of the extracts. The validated value of TPC was 84.11 ± 4.28 mg GAE/g for the sample obtained under the optimal conditions of 12.76 min at 54.08°C and 34.48% glycerol concentration. MAEG extract exhibited higher antioxidant properties compared to the decoction extract. Different phenolic compounds in the extracts were tentatively identified by LC-QTOF. MAEG concentrations from 1 mg/mL to 7.5 mg/mL were considered non-cytotoxic to NIH/3T3 fibroblasts. Furthermore, the cell viability of NIH/3T3 fibroblasts increased after being treated with MAEG extract (from 2.5 mg/mL to 7.5 mg/mL) and subjected to H2O2- induced oxidative stress compared to H2O2 treatment alone. Conclusion: Finally, MAEG can be used as a novel green extraction method for obtaining bioactive compounds for cosmetic and medicinal applications.

Comparison of the phenolic composition and biological capacities of wastewater from Origanum vulgare L., Rosmarinus officinalis L., Salvia lavandulifolia Vahl. and Thymus mastichina L. resulting from two hydrodistillation systems: Clevenger and MAE

Essential oils (EO) are probably the most marketable product obtained from medicinal plants and have an important demand in different sectors such as food industry, pharmaceuticals, cosmetics or perfumery. However, during EO distillation a large volume of waste is generated including solid residues, hydrolates and wastewater. Wastewater (WW) is mostly generated during hydrodistillation by a conventional Clevenger apparatus (CA) although during the last years a more innovative Microwave-assisted Extraction (MAE) system has increasingly been used. Regardless the system of hydrodistillation, wastewater is a residue from aromatic plants often neglected. In this work, we have compared the phenolic content and composition, extraction yield and some biological activities (antioxidant, antifungal, effects on seed germination/growth and acetylcholinesterase/AChE inhibition) of the wastewater resulting from the hydrodistillation of Origanum vulgare, Rosmarinus officinalis, Salvia lavandulifolia and Thymus mastichina obtained by a traditional Clevenger apparatus (CA) and the alternative Microwave-assisted Extraction System (MAE). The results showed a high content of phenols in all WWs, being the most important the danshensu, rosmarinic acid, as well as different isomers of salvianolic and yunnaneic acid or luteolin glycosides. However, the contents on many of these phenols ranged widely among WWs which seemed to influence the biological activities. Overall, wastewaters were especially active as antioxidants and chelators while the results in other bioactivities were rather uneven and depended in some cases on the distillation system. Consequently, the choice of the distillation method is crucial on the composition of the resulting residues and their biological activities, and therefore determines the feasibility and potential of valorization of this residue.

Maximising Recovery of Bioactive Compounds from Coffee Pulp Waste Using Microwave-assisted Extraction

Coffee pulp is a major by-product generated from coffee bean production and is generally known as waste. This study employed response surface methodology (RSM) with Box Behnken Design (BBD) to determine the impact of extraction parameters and optimise the conditions for recovery of total phenolics, flavonoids, chlorogenic acid, and caffeine from coffee pulp using a commercial microwave-assisted extraction system (MAE) for further applications. The results showed that sample to solvent ratio and ethanol concentration significantly affected the recovery yields of bioactive compounds and antioxidant capacity. There were significant interactive effects between the radiation time and sample to solvent ratio, but no significant interactive impacts between radiation time and ethanol concentration, radiation time and power, sample to solvent ratio and power, and ethanol concentration and power on recovery of bioactive compounds and antioxidant capacity of the coffee pulp extract. The optimal conditions were found to be radiation time of 85 min, sample to solvent ratio of 1:100 g/100 ml, 42.5 % (v/v) aqueous ethanol solution, and machine power of 1000 W. Under these conditions, extraction yields of total phenolic compounds, flavonoids, chlorogenic acid, and caffeine were 38.68, 27.00, 6.95, and 5.47 (mg/g DW), respectively. The extract also had high antioxidant capacities, with values measured by ABTS, DPPH, and FRAP assays as 87.95, 9.3, 65.31 (mg TE/g DW), respectively. These conditions are recommended for the recovery of bioactive compounds from coffee pulp for further applications.

Prediction of mass transfer and kinetic behavior during the extraction of high added‐value products from sour cherry ( Prunus cerasus L.) peels

In this study, deep eutectic solvent has been used in order to propose an environmentally and green method for conversion of biowaste into high added-value products. A deep eutectic solvent system consisting of citric acid/ethylene glycol mixture (1/4, molar ratio) has been prepared to extract total polyphenols from sour cherry (Prunus cerasus L.) peels. Deep eutectic solvent-based microwave-assisted extraction has been used in order to evaluate mass transfer, kinetic, and thermodynamic parameters. According to the high Biot number values (1,487.23, 2,970.83, 3,974.28), an efficient contact between the total polyphenols and the deep eutectic solvent system has been confirmed. It is observed that the total amount of phenolic substances varies between 4.29 and 33.61 mg-GAE/g of fresh material. In this study, the pseudo-second-order kinetic model (R2 > 0.90) has been successfully applied for the extraction of TPC during MAE. ∆H > 0, ∆S > 0, and ∆G < 0 denote an endothermic and spontaneous microwave-assisted extraction system for the solid–liquid extraction of TPC from sour cherry (Prunus cerasus L.) peels. Novelty impact statement Polyphenolic compounds (anthocyanins and antioxidants) were extracted from sour cherry (Prunus cerasus L.) peels. Extraction kinetics of economical and environmental MAE method has been investigated for natural antioxidants. The structure of the DES-based MAE of bioactive substances from sour cherry peels will be able to understand comprehensively according to the thermodynamic parameters.

Synthesis and Analytical Characterization of Gold Nanoparticles using Microwave-Assisted Extraction System and Study their Application in Degradation

Preparation of gold nanoparticles (AuNPs) was done by the addition of tetrachloroaurate (HAuCl4) to dodonaea viscose (L.) leaves watery extract. The procedure was performed in microwave-assisted extraction (MAE). Dodonaea viscose (L.) watery extract functions as a reducing and capping agent to synthesis AuNPs. The gold nanoparticles was identified by the changes in colour from yellow to red –purple, UV-vis spectroscopy, and surface plasmon band at (600 nm). (EDX -FESEM) and TEM instruments were used to investigate the element analysis, distribution of nanoparticles and to calculate their sizes and shapes. Energy dispersive X-ray spectra (EDX) was applied for characterization of gold nanoparticles, the detected percentage of gold nanoparticles was (0.52 wt/wt %). The result from TEM shows the nanoparticles with diameter (6-80 nm) and vary shapes. Furthermore, characterization of nanoparticles was performed before and after the formation of gold nanoparticles using FT-IR. The band appeared at 669 cm-1 indicated the gold nanoparticle formation. The synthesized gold nanoparticles have been used for degradation of 6.6 % methylene blue organic dye pollutant in aqueous solution, and also for degradation of aliphatic hydrocarbons in crude oil. The results of degradation were monitored by GC-MS. The breakage of some organic materials and the appearance of new organic materials with less molecular weight and less abundance were achieved. Through the use of gold nanoparticles, it has been observed that a large number of aliphatic compounds have disappeared, especially those with molecular weights 200-288, the loss in the molecular weight is about 40%.

In Vitro Anticoccidial Activity of Olive Pulp (Olea europaea L. var. Chemlal) Extract Against Eimeria Oocysts in Broiler Chickens.

The objective of the present study was to investigate in vitro anticoccidial effect of olive pulp (Olea europaea L var. Chemlal) extract on the destruction of Eimeria spp. oocysts isolated from infected chickens naturally. The olive pulp (OP) powder was stirred manually in aqueous ethanol in preparation for extraction using the microwave-assisted extraction system. The identification of the phenolic compounds was obtained by ultra-high-performance liquid chromatography-mass spectrometry with electrospray ionisation (HPLC-ESI-MS). The treatment of Eimeria oocyst with OP extract and standard compounds (quercetin and oleuropein) leads to their lysis as shown by the release of substances absorbing at 273nm. Our results showed that the maximum number of reduced oocysts was recorded after 8h of incubation of optimum OP extract, quercetin and oleuropein for different periods of time. Also, the number of Eimeria oocysts decreased considerably with increase concentrations after adding the optimum of OP extract in concentration ranging from 0.023 to 0.371mg/ml. Positive correlation between the optimum OP extract concentrations and the number of Eimeria oocysts reduced was R2 = 0.959. From this in vitro experiment, it can be concluded that the OP extract possesses an anti-Eimeria spp activity. To our knowledge, this is the first time that quercetin and oleuropein were tested to evaluate their anticoccidial activity. The findings of this study showed that phenolic compound of OP extract tested separately possesses anti-Eimeria spp. effect. Further studies should be carried out to test its in vivo efficacy of the OP bioactive compounds in broiler chickens.

Imidazolium-based ionic liquids with inorganic anions in the extraction of salidroside and tyrosol from Rhodiola: The role of cations and anions on the extraction mechanism

The role of cations and anions of imidazolium ionic liquid-based microwave-assisted extraction system for salidroside and tyrosol of Rhodiola was investigated. To evaluate eight kinds of imidazolium-based ionic liquid with different cations and anions on molecule level, the geometries of related IL molecules and target extracts were optimized by density functional theory at the B3LYP/6-311++G(d, p) level. Electrostatic potential (ESP) distributions of these molecules above are identified in the water modeled by the polarizable continuum model. The theoretical and experimental analysis shows there is some correlation between the characteristic values of ESP distribution and extraction yield. The more similar the ESP distribution of ILs are to salidroside and tyrosol, the higher the extraction yields are. Wider variability of ESP is beneficial to extraction. The main role of cations is interaction with extract molecules by its positive ESP regions. So the cations influence the solubility of extracts by the molecular interaction. Unlike the cations, the types of anions can affect the structure of the cell wall. The ILs with Br anion have greater ability to dissolve cellulose and break the cell wall, which made the target components within the cell could effectively dissolve. Due to the differing function of cations and anions of ILs, the ionic liquid-based MAE could provide higher extraction yields and take much shorter extraction time than conventional organic solvents.

Microwave-assisted Extraction of Natural Dyes from Coleus atropurpureus Leaves: The Effect of Solvent

A microwave-assisted extraction system was used to extract natural dyes from Coleus atropurpureus leaves. The effects of water solvent of the temperature at 100°C and 80°C as well as ethanol solvent 96% were investigated. This is done at the various material to solvent ratio (0.001, 0.0025, 0.005 g/mL) and microwave power (264, 400, 600 watt). The optimal conditions of the extraction were obtained on a water solvent of the temperature at 100°C with material to solvent ratio 0.001 g/mL, irradiation power 400 watt, extraction time 10 min, material size 35-60 mesh, the optimum yield of 44.48%. Identification of groups of pigments contained in the Coleus atropurpureus leaves is known categories tannins and flavonoids. Fourier Transform Infrared Spectroscopy was used to identify the major chemical groups in the extracted dyes.

A Rapid Method, Combining Microwave-Assisted Extraction and Gas Chromatography-Mass Spectrometry with a Database, for Determining Organochlorine Pesticides and Polycyclic Aromatic Hydrocarbons in Soils and Sediments

ABSTRACTA rapid method for determining organochlorine pesticides and polycyclic aromatic hydrocarbons in soils and sediments was developed to allow pollution surveys to be performed in emergencies. The method involves microwave-assisted extraction and uses an automated identification/quantification system with a gas chromatography mass spectrometry database. A sample (3 g) is extracted with a 3:2 v/v hexane:water mixture (10 mL) for 30 min using a microwave-assisted extraction system at 120°C. The hexane extract is then cleaned using silica gel, then analyzed by gas chromatography mass spectrometry. The total analysis time is approximately 4 h. The precision of the quantitative results and accuracy of the analyte identification were determined. The total analyte concentrations were generally comparable to (61%–110% of) the concentrations determined using a Soxhlet extraction method, but the concentrations of individual high-molecular-weight polycyclic aromatic hydrocarbons were unacceptably low compared with the concentrations determined using the Soxhlet method. However, these compounds (e.g., benzo(ghi)perylene and indeno(1,2,3-cd)pyrene) were subsequently efficiently extracted using a hexane:water:ethanol mixture. The accuracy of identification was evaluated using accurate masses determined by gas chromatography time-of-flight mass spectrometry, and the mass error was 2 ppm for 21 of the 22 compounds identified using the new method.

Rapid metal extractability tests from polluted mining soils by ultrasound probe sonication and microwave-assisted extraction systems.

Ultrasonic probe sonication (UPS) and microwave-assisted extraction (MAE) were used for rapid single extraction of Cd, Cr, Cu, Ni, Pb, and Zn from soils polluted by former mining activities (Mónica Mine, Bustarviejo, NW Madrid, Spain), using 0.01molL-1 calcium chloride (CaCl2), 0.43molL-1 acetic acid (CH3COOH), and 0.05molL-1 ethylenediaminetetraacetic acid (EDTA) at pH 7 as extracting agents. The optimum extraction conditions by UPS consisted of an extraction time of 2min for both CaCl2 and EDTA extractions and 15min for CH3COOH extraction, at 30% ultrasound (US) amplitude, whereas in the case of MAE, they consisted of 5min at 50°C for both CaCl2 and EDTA extractions and 15min at 120°C for CH3COOH extraction. Extractable concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The proposed methods were compared with a reduced version of the corresponding single extraction procedures proposed by the Standards, Measurements and Testing Programme (SM&T). The results obtained showed a great variability on extraction percentages, depending on the metal, the total concentration level and the soil sample, reaching high values in some areas. However, the correlation analysis showed that total concentration is the most relevant factor for element extractability in these soil samples. From the results obtained, the application of the accelerated extraction procedures, such as MAE and UPS, could be considered a useful approach to evaluate rapidly the extractability of the metals studied.

Optimization of Microwave-assisted Extraction of Thymoquinone from Nigella sativa L. Seeds

The high potential of thymoquinone as an ingredient and/or additive in the food, pharmaceutical and cosmetic industries has been well established in previous studies. However, its extraction from natural sources was considered in the limited studies and none of them included the microwave-assisted extraction (MAE) of a thymoquinone-rich extract and process optimization. In the present study, this high-value-added bioactive was aimed to extract from its well-known natural source, black cumin seed (&lt;em&gt;Nigella sativa&lt;/em&gt; L.), using methanol as a solvent for all of the studied extraction methods. For extraction of a compound of interest, microwave-assisted extraction system having temperature controlling function was used and its performance was compared with common extraction methods, Soxhlet and conventional solid/liquid extraction. The results indicated that the MAE system provided a rich extract containing thymoquinone, which was 2 and 7 times higher than those produced by conventional solid/liquid extraction and Soxhlet, respectively. Influences of temperature, time and solvent/solid ratio on thymoquinone yield were investigated for MAE. The solvent/solid ratio was found to have the main effect on extraction performance, whereas an interaction effect of temperature and time was significant. Variables of MAE were optimized by response surface methodology to produce a thymoquinone-rich extract. Optimal conditions for the highest yield of thymoquinone were determined as 10 minutes extraction at 30 °C, using 30 ml solvent per gram of black cumin seed. The estimated thymoquinone yield of the extract was 628 mg/kg black cumin seed. It could be concluded that the currently optimized MAE with temperature controlling function is a promising technique to produce a thymoquinone-rich extract from black cumin seeds.

Green bio-oil extraction for oil crops

The move towards a green bio-oil extraction technique is highlighted in this paper. The commonly practised organic solvent oil extraction technique could be replaced with a modified microwave extraction. Jatropha seeds (Jatropha curcas) were used to extract bio-oil. Clean samples were heated in an oven at 110 ° C for 24 hours to remove moisture content and ground to obtain particle size smaller than 500μm. Extraction was carried out at different extraction times 15 min, 30 min, 45 min, 60 min and 120 min to determine oil yield. The biooil yield obtained from microwave assisted extraction system at 90 minutes was 36% while that from soxhlet extraction for 6 hours was 42%. Bio-oil extracted using the microwave assisted extraction (MAE) system could enhance yield of bio-oil compared to soxhlet extraction. The MAE extraction system is rapid using only water as solvent which is a nonhazardous, environment-friendly technique compared to soxhlet extraction (SE) method using hexane as solvent. Thus, this is a green technique of bio-oil extraction using only water as extractant. Bio-oil extraction from the pyrolysis of empty fruit bunch (EFB), a biomass waste from oil palm crop, was enhanced using a biocatalyst derived from seashell waste. Oil yield for non-catalytic extraction was 43.8% while addition of seashell based biocatalyst was 44.6%. Oil yield for non-catalytic extraction was 43.8% while with addition of seashell-based biocatalyst was 44.6%. The pH of bio-oil increased from 3.5 to 4.3. The viscosity of bio-oil obtained by catalytic means increased from 20.5 to 37.8 cP. A rapid and environment friendly extraction technique is preferable to enhance bio-oil yield. The microwave assisted approach is a green, rapid and environmental friendly extraction technique for the production of bio-oil bearing crops.

Accuracy evaluation of ultrasound probe sonication and microwave-assisted extraction systems for rapid single extraction of metals in soils

Ultrasonic probe sonication (UPS) and microwave-assisted extraction (MAE) have been evaluated as alternatives to the conventional Standards, Measurements and Testing program (SM&T) procedures for single extraction of metals in soils, in order to reduce the extraction time and the consumption of samples and extracting agents. Optimization studies were carried out on the certified reference materials (CRMs) BCR 483 (sewage sludge amended soil) and BCR 700 (organic rich soil) for accuracy evaluation of the proposed methods. Extractable concentrations of Cd, Cr, Cu, Ni, Pb and Zn using 0.01 mol L−1 calcium chloride (CaCl2) (in BCR 483), 0.43 mol L−1 acetic acid (CH3COOH) and 0.05 mol L−1 ethylenediaminetetraacetic acid (EDTA) at pH 7.0 (in both CRMs) were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The extraction time for the CaCl2 extraction method was reduced from 3 h (conventional procedure) to 2 min by UPS or 5 min at 50 °C by MAE. Similarly, the time required for acetic acid extraction was also reduced from 16 h to 15 min by UPS or 15 min at 120 °C by MAE. Finally, the extraction time with EDTA was reduced from 1 h (conventional procedure) to 2 min by UPS or 5 min at 50 °C by MAE. For these extraction conditions proposed, quantitative extraction recoveries were obtained for most elements studied. In addition, the amount of sample and extractants was drastically reduced, maintaining the sample weight/extractant volume ratio.

Fast determination of adenosine and cordycepin in Cordyceps and its deserted solid medium

A fast analytical method for adenosine and cordycepin in Cordyceps and its deserted solid medium was developed by using a normal-phase cyan-group chromatographic column. The sample was extracted for 1.5 min using a microwave-assisted extraction system. The extraction was repeated twice. The analysis of adenosine and cordycepin was performed on an Eclipse XDB-CN column. The mobile phase was composed of methanol and water with a ratio of 7:93 (v/v) for isocratic elution. The detection wavelength was 260 nm. The composition and pH value of the mobile phase were investigated. The results showed that adenosine and cordycepin could be completely separated without matrix interference in 4.5 min. The linearity of the method was good with a linear correlation coefficient (r2) of 0. 999 8 for adenosine and 0.999 5 for cordycepin. The limits of quantification (LOQs, S/N = 10) of adenosine and cordycepin were 0.21 and 0.083 mg/L, respectively. The relative standard deviations (RSDs) of peak areas of six replicate injections were less than 2% both for intra-day and inter-day analysis. The average recoveries of adenosine and cordycepin ranged from 93.8% to 102.9% with the RSD not more than 3.62% (n = 5). The developed method is simple, fast, accurate and low-cost, and it can be used in the fast detection of adenosine and cordycepin in Cordyceps, carpohole, the deserted solid medium and its praeparatum.

Occurrence, distribution, and sources of six phenolic endocrine disrupting chemicals in the 22 river estuaries around Dianchi Lake in China

The objectives of this study are to track the occurrence, distribution, and sources of phenolic endocrine disrupting compounds (EDCs) in the 22 rivers around Dianchi Lake in China, to estimate the input and output amounts of phenolic EDCs in the water system, and to provide more comprehensive fundamental data for risk assessment and contamination control of phenolic EDCs in aquatic environment. Six phenolic EDCs were systematically evaluated in water and surface sediment in the estuaries of those rivers. The water and sediment samples were preconcentrated by solid-phase extraction system and microwave-assisted extraction system, respectively. Phenolic EDCs were analyzed by GC-MS (Thermo Fisher Scientific, USA) after derivatization. Phenolic EDCs were found ubiquitously in the aquatic environment. The total concentrations ranged from 248 to 4,650 ng/L in water, and 113 to 3,576 ng/g dry weight in surface sediment. The residue amount of phenolic EDCs in Dianchi Lake was 258 kg/a. Concentrations of the phenolic EDCs in the Lake decreased with increase in distance to the estuaries of those rivers which run through urban and industrial areas. The rivers seriously contaminated by phenolic EDCs were Xin River, Yunliang River, Chuanfang River, Cailian River, Jinjia River, Zhengda River, and Daqing River which run through the old area of Kunming City. Satisfying correlations were observed between the concentrations of the target compounds in water and in surface sediment. NP1EO, NP2EO, and BPA were identified as the three predominant phenolic EDCs. There were significant correlations between phenolic EDCs and many basic water quality parameters. Urban and industrial areas are the major contributors for phenolic EDCs, especially in Kunming City. Compositional profiles of phenolic EDCs in surface sediment were similar to those in river water. The concentrations of phenolic EDCs in the rivers located in the northwest part of the valley were very high, and posed a potential risk to aquatic organisms and even human. The concentrations of NP2EO, NP1EO, and BPA were at moderate levels of other areas. The basic water quality parameters (TOC, TN, DO, and pH) play important roles on the distribution, fate, and behavior of phenolic EDCs in the valley.

Microwave-assisted extraction performed in low temperature and in vacuo for the extraction of labile compounds in food samples

In this study, low temperature vacuum microwave-assisted extraction, which simultaneous performed microwave-assisted extraction (MAE) in low temperature and in vacuo environment, was proposed. The influencing parameters including solid/liquid ratio, extraction temperature, extraction time, degree of vacuum and microwave power were discussed. The predominance of low temperature vacuum microwave-assisted extraction was investigated by comparing the extraction yields of vitamin C, β-carotene, aloin A and astaxanthin in different foods with that in MAE and solvent extraction, and 5.2–243% increments were obtained. On the other hand, the chemical kinetics of vitamin C and aloin A, which composed two different steps including the extraction step of analyte transferred from matrix into solvent and the decomposition step of analyte degraded in the extraction solvent, were proposed. All of the decomposition rates ( K 2) for the selected analyte in low temperature, in vacuo and in nitrogen atmosphere decreased significantly comparing with that in conventional MAE, which are in agreement with that obtained from experiments. Consequently, the present method was successfully applied to extract labile compound from different food samples. These results showed that low temperature and/or in vacuo environment in microwave-assisted extraction system was especially important to prevent the degradation of labile components and have good potential on the extraction of labile compound in foods, pharmaceutical and natural products.

Microwave-assisted extraction of polyphenols from Camellia oleifera fruit hull.

The abundant fruit hulls of tea-oil tree (Camellia oleifera) are still underutilized and wastefully discaded to pollute the environment. In order to solve this problem and better utilize the fruit hulls of C. oleifera, a microwave-assisted extraction system was used to extract their polyphenols using water as the extraction solvent. A central composite design (CCD) was used to monitor the effects of three extraction processing parameters – liquid:solid ratio (mL/g), extraction time (min) and extraction temperature (°C) – on the polyphenol yield (%). The results showed that the optimal conditions were liquid:solid ratio of 15.33:1 (mL/g), extraction time of 35 min and extraction temperature of 76 °C. Validation tests indicated that under the optimized conditions the actual yield of polyphenols was 15.05 ± 0.04% with RSD = 0.21% (n = 5), which was in good agreement with the predicted yield. Phenolic compounds in the extracts were analysed by HPLC, and gallic acid was found to be the predominant constituent. The total flavonoid content in the extracts was determined and high total flavonoid content was revealed (140.06 mg/g dry material).

Microwave-assisted extraction of phenolic antioxidant compounds from peanut skins

A microwave-assisted extraction system was used to extract phenolic antioxidants from peanut skins. The effects of microwave power (10%, 50%, 90% nominal), irradiation time (30, 90, 150 s) and sample mass (1.5, 2.5, 3.5 g) on total phenolic content (TPC), ORAC (oxygen radical absorbance capacity) level and resveratrol content of peanut skin extracts (PSE) were investigated. Peanut skins were extracted with 37.5 ml of 30% ethanol (EtOH) in water. A response surface method was used to estimate optimum extraction conditions, based on TPC, ORAC level and resveratrol content. The maximum predicted TPC, under the optimised conditions (90% microwave power, 30 s irradiation time and 1.5 g skins), was 143.6 mg gallic acid equivalent (GAE)/g skins. The highest ORAC value was 2789 μmol trolox equivalents (TE)/g skins, which occurred at 90% power, 150 s and 1.5 g of skins. Resveratrol was identified in PSE by LC–MS–MS analysis.

Dynamic microwave-assisted extraction of flavonoids from Saussurea medusa Maxim cultured cells

An approach for automated, continuous and rapid extraction of flavonoids from Saussurea medusa Maxim dried cell cultures has been developed in a new-designed dynamic microwave-assisted extraction system. The main factors affecting the extraction process namely power of microwave irradiation, liquid/solid ratio, flow rate of solvent and irradiation time were optimized. The yield of flavonoids reached 4.97% in 60 min under the optimum microwave-assisted extraction conditions: 1200 W of radiation power, 50:1 (v/w) of the liquid/solid ratio, and 50 ml s −1 of solvent flow rate. The dynamic microwave-assisted extraction showed obvious advantages in short duration and high efficiency to extract flavonoids without causing degradation of target components from the S. medusa dried cell cultures in comparison with the dynamic solvent extraction without microwave assistance.

Solvent effects on focused microwave assisted extraction of polyphenolic acids from Eucommia ulmodies

An open microwave-assisted extraction system was used to extract gallic acid, protocatechuic acid, chlorogenic acid and caffeic acid from Eucommia ulmodies. The effect of extraction variables, especially solvent, on the recoveries of these polyphenolic compounds was investigated using factorial design. As extracting solvent for these compounds, methanol produced a higher recovery than pure water. For straight chain alcohol solvents, the lower the carbon number, the higher the recoveries of the polyphenolic acids. The optimal ratio of methanol:water:glacial acetic acid in the solvent mixture used in microwave-assisted extraction was 2:8:0.3 (v/v) and this solvent could be directly used as the mobile phase in HPLC separation without additional intermittent treatment as reported in literature. The extraction under the condition of 50% microwave power and 30 s irradiation at a solvent:sample ratio of 10 (mL/g) was found to be the most advantageous. The repeatability test of extraction and chromatographic analysis was satisfactory for the analysis of these polyphenolic compounds.