Effect of microwave‐assisted extraction on the release of polyphenols from ginger (Zingiber officinale)

The significance of different variables viz. temperature, time and solvent at constant power in microwave‐assisted extraction (MAE) process of ginger was studied and compared with conventional method. Aqueous ethanol (50%) provided higher yields of extract as well as the highest release of total polyphenols (TPP) than alcoholic solvents. The reason could be the high dielectric constant of aqueous ethanol as compared to alcohols. Microwave heating being a volumetric process, an exposure time of 1 min was found to be sufficient. The better penetration of microwaves and greater solubility at higher temperature resulted in higher yield of TPP and [6]‐gingerol. The resultant extract showed higher radical scavenging activity (RSA) values. Thus, MAE allowed higher recoveries compared to conventional extraction process, with improvement in the quantity and quality of extract in very short period of time.     

Microwave-assisted extraction of betalains from red beet (Beta vulgaris)

The use of microwave assisted extraction (MAE) was investigated in this work for the extraction of betalains from diced red beets. Several treatments with different combinations of time, power and duty cycle applied to the samples were studied. The combination of 400 W and 100% duty cycle for 90–120 s resulted in the highest amount of recovered betanines; whereas at 140–150 s the highest amount of betaxanthins was obtained. The addition of ascorbic acid (0.040 mol/L) to the extracting solvent and the development of a two-step MAE process with a cooling period in-between and after processing steps led to an enhancement in the amount of pigments obtained. The effect of extraction time at each extraction step on betalains yield was determined by applying a factorial design and surface plots were constructed. The duration of the second step significantly affected the yield of betanines and betaxanthins obtained (p < 0.05). A prediction model was proposed and validated to meet the optimal extraction times. Betalain yields obtained by MAE were twice as high as those obtained during conventional extraction and conventional extraction at 80 °C.     

The optimization of microwave-assisted extraction of decursin from Angelica gigas Nakai root

Response surface methodology was used to display the characteristics of microwave‐assisted extraction (MAE) of soluble solids and decursin from Angelica gigas Nakai root, thereby allowing MAE conditions to be optimized. These included ethanol concentration, microwave power and extraction time. The maximal solid yield was predicted to be 44.2% under conditions of 44.9% ethanol concentration, 115.6 W microwave power and 5.8 min extraction time. Decursin content of the extract was estimated to be maximal at 2.52% using 97.7% ethanol, 90.2 W microwave power, and 6.1 min extraction time. The estimated optimal MAE conditions (67% ethanol, 100 W and 6 min) to maximize both components were verified by comparing estimated values with experimental values (42.2% soluble solids, 2.2% decursin), which were higher than those (35.8% solids, 2.0% decursin) obtained by conventional reflux extraction (60% ethanol, 95 °C and 6 h).     

响应面法优化石上柏穗花杉双黄酮提取工艺

采用响应面法优化石上柏穗花杉双黄酮微波提取工艺条件。研究了微波功率、提取时间、固液比和提取温度等对石上柏中穗花杉双黄酮得率的影响,并采用响应面实验设计和多元二次回归分析,优化了此提取工艺。通过实验得出穗花杉双黄酮最佳提取工艺条件:固液比为1:15 g/mL,微波功率为400 W,提取时间为37 min,提取温度为47℃。在此条件下,穗花杉双黄酮的得率达到了0.33%±0.08%。与乙醇回流提取法和索氏提取法相比,该方法节省时间、节约能量、提取效率高、控制方便。可用于石上柏穗花杉双黄酮的提取。     

Microwave-assisted extraction of phenolic compounds from wine lees and spray-drying of the extract

Most research on extraction of phenol compounds from wine by-products and commercial exploitation of extracts use grape seeds and/or skins as raw materials. Looking for alternative antioxidants sources, obtaining antioxidant extracts from wine lees (also known as dregs), a sub-exploited by-product of winemaking process, is here presented. Microwave-assisted extraction (MAE) of phenolic compounds from wine lees has been optimized using the total phenols index, the ORAC values and yield of the extraction as response variables. Under the optimal working conditions, the proposed MAE method provides better extraction efficiency in a much shorter time (17 min) than the conventional extraction method for phenolic compounds (24 h). The liquid extract obtained by MAE was spray-dried. The type and amount of excipients used, as well as the spray-drying temperature, were optimized in order to minimize the oxidation of phenolic compounds and maximize the yield of the spray-drying process. The total phenols index in the dried extract thus obtained was 36.8% (expressed as gallic acid), showing an ORAC value of 3930 μmol TE/g. Additionally, Mv3G, Cm-Mv3G, myricetin, quercetin, quercetin-3-β-glucoside, caffeic acid and p-coumaric acid were quantified in the dry extract by HPLC–DAD. The results indicate that wine lees antioxidant extracts can be a suitable and cheap alternative to those obtained from grape seeds or skins.     

Effect of energy density and citric acid concentration on anthocyanins yield and solution temperature of grape peel in microwave-assisted extraction process

In order to verify the sensitivity of anthocyanins (Acys) yield of grape peel to the energy density (microwave power for a given unit of volume) and citric acid concentration in microwave-assisted extraction (MAE) process, the effect of energy density and citric acid concentration in MAE process were investigated. The results indicated that, Acys yield was more sensitive to energy density than to microwave power. The correlation between Acys yield and energy density follows well Gaussian function, suggested by higher R squares (R² > 0.9399). Exponential decay model can well describe the correlation between Acys yield and citric acid concentration, or between solution temperature rise and energy density. The solution temperature was a linear function of citric acid concentration and extraction time. Energy density was the most significant factor affecting the Acys yield, followed by citric acid concentration, ratio of liquid to solid and extraction time (p < 0.05).     

Structural modification by different pretreatment methods to enhance microwave-assisted extraction of β-carotene from carrots

Since the structure of a material is a key factor influencing the extraction efficiency, any means to modify the structure to enhance extraction is attractive. As limited information is available on the effect of sample pretreatment prior to extraction on the extractability of a bioactive compound, the effects of selected pretreatment methods, i.e., soaking in citric acid, blanching in water as well as in citric acid, on the sample structure and subsequent microwave-assisted extraction (MAE) were investigated; carrots and β-carotene (as well as carotenoids) were selected as the test material and bioactive compound, respectively. A suitable condition to extract β-carotene in terms of the microwave power and extraction time was determined. Comparison between MAE and Soxhlet extraction was also made. At the optimized condition the contents of β-carotene and total carotenoids extractable from carrots blanched in water (29.74 and 58.04 mg/100 g dry basis) and in citric acid (32.08 and 61.62 mg/100 g dry basis) were significantly higher than those from the untreated carrots (23.26 and 51.79 mg/100 g dry basis). The antioxidant activities of the extracts obtained from carrots blanched in water and in citric acid were also higher than that from carrots with no pretreatment. Comparison between MAE and Soxhlet extraction revealed that the extract from MAE contained lower amounts of β-carotene and total carotenoids and exhibited lower antioxidant activity; the required MAE time was significantly shorter, however.     

Optimization of various extraction methods for quercetin from onion skin using response surface methodology

Quercertin and typical flavonoids present in onion skin draw interest due to bioactive properties. For utilizing quercetin from onion skin, conventional solvent extraction (CSE), microwave assisted extraction (MAE), and ultrasound assisted extraction (UAE) were employed. Statistic models of each method were proposed to estimate the best possible yield of quercertin employing response surface methodology (RSM). The effects of several independent variables including concentration of ethanol, provided power or the temperature, and reaction time were investigated. From 1 g sample of dried onion skin, the highest yield of each method could be achieved at 16.5 min of process time under 59.2°C for CSE with 59.3% ethanol, 117 s for MAE with 69.7% ethanol, and 21.7 min for UAE using power of 606.4 W with 43.8% ethanol. The most productive method was MAE, whose maximum yield was 20.3 and 30.8% higher than UAE and CSE, respectively.     

Optimization of microwave-assisted extraction of anthocyanins in red raspberries and identification of anthocyanin of extracts using high-performance liquid chromatography – mass spectrometry

Anthocyanins (Acys) are naturally occurring compounds that impart color to fruit, vegetables, and plants. The extraction of Acys from red raspberry (Rubus idaeus L. var. Heritage) by microwave-assisted process (MAP) was studied. A central composite rotate design (CCRD) was used to obtain the optimal conditions of microwave-assisted extraction (MAE), and the effects of operating conditions such as the ratio of solvents to materials, microwave power and extraction time on the extraction yield of Acys were studied through response surface methodology (RSM). The optimized conditions of MAE were ratio of solvents to materials 4:1 (ml/g), extraction time 12 min, and microwave power 366 W. Under these conditions 43.42 mg of Acys from 100 g of fresh fruits (T _Acy, expressed as cyanidin-3-glucoside), approximately 98.33% of the total red pigments, could be obtained by MAE. The Acys compositions of extracts were identified by high-performance liquid chromatography – mass spectrometry (HPLC-MS), 12 kinds of Acys had been detected and 8 kinds of Acys were characterized. Result indicated that cyanidin-3-sophoroside, cyanidin-3-(2 ^G -glucosylrutinoside), cyanidin-3-sambubioside, cyanidin-3-rutinoside, cyanidin-3-xylosylrutinoside, cyanidin-3-(2 ^G -glucosylrutinoside), and cyanidin-3-rutinoside were main components in extracts. In addition, in comparison with the conventional solvent extraction, MAE is more efficient and rapid to extract Acys from red raspberry, due to the strong disruption of fruit tissue structure under microwave irradiation, which had been observed with the scanning electron microscopepy (SEM). However, the Acys compositions in extracts by both the methods were similar, which were investigated using HPLC profile.     

Green extraction of soluble dietary fibre from coffee silverskin: impact of ultrasound/microwave-assisted extraction

Coffee silverskin (CSS), a potential source of soluble dietary fibre (8%–11%), is a major coffee by-product obtained during the coffee roasting process. Ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) have been considered as efficient and economic novel extraction techniques. In this study, UAE, MAE and simultaneous ultrasound–microwave-assisted extraction (UMAE) techniques were investigated for soluble dietary fibre (SDF) extraction from CSS and compared with conventional solvent extraction (CSE). The highest recovery rate of SDF was accomplished by UMAE (42.7 ± 0.4%), which was 1.5-fold, 1.9-fold and 1.2-fold of the recovery rates achieved by CSE, UAE and MAE, respectively. The extraction time of UMAE was 20 min, which was the same as UAE and MAE, and 4.5-fold less than CSE. It implied that the combination of UAE and MAE could enhance the extraction process by increasing the recovery rate as well as by reducing extraction time as compared with CSE or other individual novel extraction methods applied. Nutritional composition and physicochemical characteristics of the SDF extracts from CSS were also investigated in the study.     

Optimization of microwave-assisted extraction of triterpene saponins from defatted residue of yellow horn (Xanthoceras sorbifolia Bunge.) kernel and evaluation of its antioxidant activity

Microwave-assisted extraction (MAE) of triterpene saponins from defatted residue of yellow horn (Xanthoceras sorbifolia Bunge.) kernel was optimized in this study. Compared with the conventional extraction methods ultrasonic-assisted extraction (UAE) and heat reflux extraction (HRE), MAE possessed higher efficiency for the extraction of triterpene saponins. The MAE conditions including extraction temperature, extraction duration, irradiation power, ethanol concentration, ratio of solvent to material and extraction cycles were studied and optimized. The optimum extraction parameters were as follows: 51 °C, 7 min, 900 W, 32 ml/g, 42% (v/v) ethanol and 3 cycles. Under the above conditions, the highest extraction yield of triterpene saponins reached 11.62 ± 0.37% of defatted kernel, which was much higher than those of conventional extraction methods. In addition, MAE extract of triterpene saponins exhibited substantial free radical-scavenging activity with an IC₅₀ value of 0.782 mg/ml.

Industrial relevance

Large amounts of defatted kernels of yellow horn are discarded after oil extraction in biodiesel production. It is not only an environmental pollution but also a waste of bioresource. In fact, the residue still has potential for bioactive and medicinal use. Therefore, this study focused on the utilization of defatted kernels of yellow horn by optimizing MAE and evaluation of the antioxidant activity of the resulting extract. MAE provided a better way to deal with defatted kernels of yellow horn as a utilization of waste material of the bioactive resource in food and pharmaceutical industry.     

小麦胚芽VE的微波萃取工艺和神经网络模型的研究

本文研究了微波萃取小麦胚芽中维生素E的方法。考察了溶剂浓度，微波萃取时间，液固比，预浸取时间对萃取率的影响。与常规萃取方法相比，当小麦胚芽5g，液固比6：1(V／W)，微波功率468W时，微波萃取时间2min，乙醇浓度50％时，维生素E的萃取率可达到16．65mg／100g，其效率远大于常规萃取方法。因此微波萃取小麦胚芽中维生素E具有时间短，效率高的特点。本文还运用取得的实验数据建立了小麦胚芽中VE微波萃取的BP神经网络模型。并验证了模型的正确性。     

Lipid content of frozen fish: Comparison of different extraction methods and variability during freezing storage

In this work, a microwave-assisted extraction (MAE) methodology was compared with several conventional extraction methods (Soxhlet, Bligh & Dyer, modified Bligh & Dyer, Folch, modified Folch, Hara & Radin, Roese-Gottlieb) for quantification of total lipid content of three fish species: horse mackerel (Trachurus trachurus), chub mackerel (Scomber japonicus), and sardine (Sardina pilchardus). The influence of species, extraction method and frozen storage time (varying from fresh to 9 months of freezing) on total lipid content was analysed in detail.The efficiencies of methods MAE, Bligh & Dyer, Folch, modified Folch and Hara & Radin were the highest and although they were not statistically different, differences existed in terms of variability, with MAE showing the highest repeatability (CV = 0.034). Roese-Gottlieb, Soxhlet, and modified Bligh & Dyer methods were very poor in terms of efficiency as well as repeatability (CV between 0.13 and 0.18).     

Microwave‐assisted extraction of secoisolariciresinol diglucoside from flaxseed hull

Microwave‐assisted extraction (MAE) of secoisolariciresinol diglucoside (SDG) from defatted flaxseed hull (DFH) was studied. The effects of pre‐soaking methods and extraction parameters (ethanol concentration (0–100%, v/v), microwave energy input (50–390 W), liquid to solid ratio (5:1 to 40:1, mL g^?1) and irradiation time (10–330 s)) on the SDG yield were investigated. Response surface methodology (RSM) was applied to optimise the MAE conditions as irradiation time 90.5 s, ethanol concentration 40.9% (v/v), liquid to solid ratio 21.9:1 (mL g^?1) and microwave power 130 W. The SDG recovery from DFH with MAE was 11.7 g SECO kg^?1 DFH (on dry‐weight basis), which was significantly higher than that of stirring extraction (10.0 g SECO kg^?1 DFH) and Soxhlet extraction (7.60 g SECO kg^?1 DFH). Compared with stirring extraction and Soxhlet extraction, MAE showed its superiority in improving SDG yield and saving time and energy. Copyright © 2007 Society of Chemical Industry     

Microwave-assisted extraction of chlorogenic acids from green coffee beans

Microwave-assisted extraction (MAE) has been considered as a potential alternative to conventional solvent extraction for the isolation of phenolic compounds from plants. Aqueous and alcoholic extracts of green coffee bean obtained by MAE were quantitatively analysed for total yield of extracts, chlorogenic acids, caffeine and total polyphenol content. The extracts were also evaluated for radical-scavenging activity, using 1,1-diphenyl-β-picrylhydrazyl radical. Under optimum conditions of time (5 min), temperature (50 °C) and wattage (800 W), the maximum chlorogenic acids and caffeine could be extracted with water as solvent. The extracts contained chlorogenic acids and caffeine in the ranges of 31–62% and 22–40%, respectively. The yields of MAE under optimum conditions were higher than those from the conventional solvent extraction at 5 min and 50 °C and the extracts showed radical-scavenging activity of >75%, even at the concentration of 25 ppm. The MAE process can thus be predicted and controlled for industrial application.     

Comparative evaluation of microwave‐assisted extraction and preheated solvent extraction of bioactive compounds from a plant material: a case study with cabbages

Preheated solvent extraction (PSE) was evaluated via the analysis of the extraction kinetics, microstructure of extracted samples and energy consumption as alternative to microwave‐assisted extraction (MAE). Cabbage outer leaves and ethanol were used as test material and extraction solvent, respectively. MAE was first optimised in terms of glucosinolates and phenolics yields; total antioxidant activity of the extracts was also assessed. MAE at a specific absorbed power of 0.37 W g^?1 for 9 min was selected as optimum condition to extract glucosinolates and phenolics, while PSE was optimised at 6 min of the extraction. The highest normalised total glucosinolates and phenolic contents as well as antioxidant activities of the extracts obtained via MAE were not significantly different from those obtained via PSE. Confocal laser scanning microscopy revealed no significant differences in cabbage cell damages rendered by MAE and PSE. PSE nevertheless exhibited slightly higher specific energy consumption than MAE.     

微波法和水蒸气蒸馏法提取丁香精油的研究

以丁香为原料,分别采用微波法和水蒸气蒸馏法提取精油,探讨微波萃取对丁香精油提取率和精油品质的影响。以丁香精油提取率为指标,通过正交试验优化微波提取条件,采用气相色谱-质谱(GC-MS)法鉴定其化学成分,并与水蒸气蒸馏法提取的精油进行比较。结果表明,微波萃取丁香精油的最佳工艺参数为微波功率300 W、料液比1∶4(m∶V)、微波时间25s、提取次数4,该条件下精油的提取率可达到20.65%,远远高于水蒸气蒸馏法的11.33%;从该精油中鉴定出19种成分,其中3种丁香精油有效成分的得率分别为丁香酚13.2%、石竹烯4.4%、乙酰基丁香酚2.2%,石竹烯和乙酰基丁香酚得率分别是水蒸气蒸馏精油的2.8倍和2倍。微波萃取是丁香精油较有效的提取方式。     

微波辅助提取葡萄皮渣中白藜芦醇的工艺研究

目的优化葡萄皮渣中白藜芦醇的微波辅助提取工艺。方法通过单因素试验,选择微波时间、料液比以及微波功率为自变量,白藜芦醇提取率为考察指标,采用正交试验设计分析研究各自变量对多糖提取率的影响。经极差与方差分析,从而获得最适的提取工艺条件。结果在微波提取时间70 s、料液比1:20(m:V)、微波作用功率为600 W的条件下获得白藜芦醇提取率为0.284%,相比有机溶剂乙醇提取法的提取率增加了42%。结论本研究可为葡萄皮渣的再利用与开发提供参考。     

山茱萸籽总黄酮的响应曲面法优化微波辅助提取工艺的研究

目的:利用微波辅助提取技术对山茱萸籽总黄酮的提取工艺进行研究。方法:以芦丁为对照品,采用紫外-分光光度法测定山茱萸籽中总黄酮的含量,以总黄酮含量为考察指标,采用响应曲面优化法(RSM)优化山茱萸籽总黄酮的提取工艺。结果:优化的山茱萸籽总黄酮微波辅助提取工艺参数为:微波功率350W,乙醇体积分数50%,液料比20mL/g,提取时间13min。在此最佳条件下,山茱萸籽总黄酮的一次提取率为6.68%。结论:山茱萸籽含有较高的总黄酮含量,所确定的提取工艺提取率高、速度快、操作简便。     

Optimized microwave-assisted extraction of total phenolics (TP) from Ipomoea batatas leaves and its antioxidant activity

An efficient microwave-assisted extraction (MAE) technique was employed to extract total phenolics (TP) from sweetpotato [Ipomoea batatas (L.) Lam.] leaves (TPSL). The optimal conditions for microwave-assisted extraction of TPSL were determined by response surface methodology. A face-centered cubic design (FCD) was applied to evaluate the effects of three independent variables (microwave power, extraction time and ethanol proportion) on the recovery of TPSL. The correlation analysis of the mathematical-regression model indicated that quadratic polynomial model could be employed to optimize the microwave extraction of TPSL. From response surface plots, microwave power, extraction time and ethanol proportion exhibited independent and interactive effects on the extraction of TPSL. The optimal conditions to obtain the highest recovery of TPSL were as follows: microwave power, 302 W; extraction time, 123 s; ethanol proportion, 53% (v/v). Under these optimal conditions, the experimental values agreed with the predicted ones by analysis of variance. It indicated high fitness of the model used and the success of response surface methodology for optimizing TPSL extraction. After method development, the antioxidant activity of the MAE extract was preliminarily evaluated. MAE showed obvious advantages in terms of high extraction efficiency and antioxidant activity of extract with in shortest extraction time.Industrial Relevance: Sweet potato leaves have been neglected except for a partial use as livestock feed in China. This study describes the response surface optimization of microwave-assisted extraction (MAE) process for the enhanced recovery of total phenolics from sweetpotato leaves (TPSL). MAE showed obvious advantages in terms of high extraction efficiency and antioxidant activity of extract within shortest extraction time. TPSL obtained using MAE showed potential for use in health-care food and pharmaceutical industry.