Ultrasound Extraction — an overview, ScienceDirect Topics

Ultrasound Extraction

Ultrasound-assisted extraction (UAE) is generally the term used to refer the extraction process from solid samples (typically, leaching or solid–liquid extraction).

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Acceleration and Automation of Solid Sample Treatment

María Dolores Luque de Castro, José Luis Luque García, in Techniques and Instrumentation in Analytical Chemistry , 2002

Ultrasound-assisted extraction versus microwave-assisted leaching

Ultrasound-assisted extraction provides several interesting advantages over microwave-assisted leaching, namely:

Ultrasound-assisted extraction is occasionally faster than microwave-assisted leaching [ 57 ]

In acid digestions, the ultrasonic procedure is safer as it requires no high pressure

or temperature [ 68 ],

In many cases, the whole procedure is simpler as it involves fewer operations and is thus less prone to contamination.

On the other hand, ultrasound-assisted extraction has the following shortcomings relative to microwave-assisted extraction:

Particle size is a critical factor in ultrasound-assisted applications [ 68 ].

Ultrasound-assisted procedures are usually less robust than microwave-assisted ones since, as suggested by Cencic-Kobda and Marcel [ 45 ], ageing of the ultrasonic probe surface can alter the extraction efficiency.

Classification of Extraction Methods

Dr.Subhash C. Mandal M. Pharm., Ph.D, . Dr.Anup Kumar Das M. Pharm., Ph.D, in Essentials of Botanical Extraction , 2015

6.1.1.2.3 Advantages and Disadvantages of UAE

Ultrasound-assisted extraction is a simple, inexpensive and efficient alternative to conventional extraction techniques. The main benefits of use of ultrasound in solid–liquid extraction include the faster kinetics and increase of extraction yield. Ultrasound can also reduce the operating temperature allowing the extraction of thermolabile compounds. Compared with other novel extraction techniques such as microwave assisted extraction, the ultrasound apparatus is cheaper and is quite ease in operation. Moreover ultrasound-assisted extraction, like Soxhlet extraction, can be used with any solvent for extracting a wide variety of bioactives. However, the effects of ultrasound on extraction yield and extraction kinetics may be linked to the nature of the plant matrix. Therefore, those two factors must be considered carefully in the design of ultrasound assisted extractors. We hereby present a detailed comparison chart of UAE with other well known extraction processes.

Methods based on Soxhlet extraction have traditionally been used as references to assess the performance of methods based on other principles, including ultrasound. The main advantages of UAE over conventional Soxhlet extraction are as follows.

Cavitation increases the polarity of the system, including extractants, analytes and matrix; this increases the extraction efficiency, which can be similar to or greater than that of conventional Soxhlet extraction.

Ultrasound-assisted leaching allows the addition of a coextractant to increase further the polarity of the liquid phase.

It also allows the leaching of thermolabile analytes, which are altered under the working conditions of Soxhlet extraction.

The operating time is invariably shorter than with Soxhlet extraction.

However, ultrasound-assisted leaching is at a disadvantage with respect to Soxhlet extraction in other respects, as follows.

In batch systems, which are the most widely used, the solvent cannot be renewed during the process, so its efficiency is a function of its partitioning coefficient.

The need for altering and rinsing after extraction lengthens the overall duration of the process, and increases solvent consumption and the risk of losses and/or contamination of the extract during handling.

UAE provides several interesting advantages over microwave-assisted leaching, as follows:

It is sometimes faster.

In acid digestions, the ultrasonic procedure is safer than the microwave one, as the former does not require high pressure or high temperature.

In many cases, the ultrasonic procedure is simpler, as it involves fewer operations and is thus less prone to contamination.

However, ultrasound-assisted extraction has the following shortcomings when compared to microwave assisted extraction.

It is usually less robust, as aging of the surface of the ultrasonic probe can alter extraction efficiency.

Particle size is a critical factor in ultrasound assisted applications.

Ultrasound-Assisted Metal Extractions☆

Conclusions

Ultrasound-assisted extraction can be used as an alternative to traditional sample preparation methods for elemental analysis and speciation where matrix separation rather than complete matrix elimination is performed. Sonication methods usually involve mild treatments which meet an important requirement for speciation, that is, extraction of the species of interest without changes in their integrity. As a result of the decreased amount of matrix released during sonication treatments, matrix interferences can also be reduced. Additionally, ultrasonic treatments provide a significant speeding up of those methods requiring long and tedious extractions (e.g., sequential extraction of metals from solid environmental samples). So far, analytical results obtained on applying ultrasound for sample preparation are very promising, and new developments are expected on the topics addressed in the present work. The use of cup-horn systems can to extend applications of UAE. On-line solid–liquid extraction with the use of ultrasound will require specially designed ultrasonic cells to further simplify sample treatment. Routine laboratories can easily implement UAE.

Ultrasound Extractions☆

Ultrasound-Assisted Extraction for Solid Samples

Ultrasound-assisted extraction (UAE) is generally the term used to refer the extraction process from solid samples (typically, leaching or solid–liquid extraction). As a part of an analytical process, sample preparation is considered to be an essential step so that the entire process can be simplified. In this case, the ability of many analytical systems to handle liquid samples has brought about the development of separation methods which fulfill a main objective, that is, to obtain quantitative analyte leaching from the solid matrix using a suitable solvent, with little or no matrix release, so that matrix effects can be kept to a minimum during the measurement steps. For speciation applications, a last condition of a solid–liquid extraction method must be the maintenance of the species integrity during treatment.

Table 2 shows the most relevant methods for treatment of solid samples based on analyte extraction. Different extraction techniques used with liquid samples have also been added. An important requirement of most techniques shown is that solvents at high temperature (i.e., at boiling point) or pressure must be used. In contrast, operation with ultrasonic processors can be performed at ambient temperature and normal pressure, and mild chemical conditions are used in most cases. 10, 11

Table 2 . Main extraction techniques for solid and liquid samples in analytical chemistry 10, 11

Extraction technique Principle of the technique
Classical solid–liquid extraction Also known as shake-flask extraction. Sample is shaken together with the appropriate solvent in a container and the liquid separated by filtration
Soxhlet Sample is placed in a disposable, porous container (thimble); constantly refluxing solvent flows through the thimble and leaches out analytes that are collected continuously
Soxtec Automated Soxhlet. A combination of hot solvent leaching and Soxhlet extraction; sample in thimble is first immersed in boiling solvent and then the thimble is raised for Soxhlet extraction with solvent refluxing
Forced-flow leaching (FFL) Sample is placed in a flow-through tube, and solvent is pumped or pushed through high pressure nitrogen gas, while the tube is heated near the boiling point of solvent
Accelerated solvent extraction (ASE) Also known as pressurized fluid extraction (PFE) and pressurized solvent extraction (PSE). Sample is placed in a sealed container and heated to a temperature higher than its boiling point, causing pressure in the vessel to rise. Pressurized hot water extraction (PHWE) is used when solvent is water at elevated temperature and pressure (subcritical water)
Microwave-assisted extraction (MAE) Rapid heating of the sample solvent mixture in closed vessels for a more efficiency extraction. Microwave-assisted extraction reduces time and solvent consumption
Supercritical fluid extraction (SFE) Sample is placed in flow-through container and a supercritical fluid (e.g., CO2) is passed through sample; after depressurization, extracted analyte is collected in solvent or trapped on adsorbent and desorbed by rinsing with solvent
Matrix solid phase dispersion (MSPD) Sample is grounded and dispersed in a solid phase sorbent in excess. The homogeneous mixture is packed into a syringe. A solvent is used and the eluated is collected
Ultrasound-assisted extraction (UAE) Finely divided sample in a container is immersed in an ultrasonic bath with solvent and subjected to ultrasonic irradiation; an ultrasonic probe or a sonoreactor can also be used
Direct thermal extraction (DTE) Volatiles analytes can be thermally extracted directly from solid samples without solvents. The sample is heated (controlled) to much higher temperatures (as high as 350°C) than Purge and Trap
Purge and trap (PT) Also known as dynamic headspace extraction. Sample is placed in a sealed vessel and purged with an inert gas. Volatile compounds are then retained in trap. Desorption of volatile analytes is carried out by heating the trap into a gas chromatograph
Liquid–liquid extraction (LLE) Analyte, usually in an aqueous sample, is partitioning between two different phases (aqueous sample and organic solvent). A separation funnel is frequently used. Continuous liquid–liquid extractors are also available
Liquid phase microextraction (LPME) Different miniaturized approaches derived from conventional LLE. Some examples are: (i) single-drop microextraction (SDME) uses a microsyringe to expose an extractant drop to headspace sample or directly within sample; (ii) dispersive liquid–liquid microextraction (DLLME) uses a second solvent or dispersing solvent in order to improve extraction of analytes; (iii) liquid–liquid–liquid microextraction (LLLME), analyte is extracted from the aqueous sample into an organic layer with lower density and simultaneous back-extraction into an aqueous drop; (iv) hollow-fiber liquid phase microextraction (HF-LPME), a water-immiscible extractant is immobilized in the pores of a hollow fiber supported by a microsyringe
Solid phase extraction (SPE) Usually, a solid phase into a cartridge is used as sorbent for analytes or interferences from a liquid sample. An elution step is then used to recovery analyte or to remove interferences
Stir-bar sorptive extraction (SBSE) In this case a liquid sample is exposed to a magnetic stir bar coated with an extractant phase. Miniaturized SBSE or stir bar sorptive microextraction (SBSME) is also used
Solid phase microextraction (SPME) Miniaturization of SPE. Usually, a fiber coated with an extracting phase replaces the cartridge used in SPE. Analyte desorption can be thermal or by a solvent. Other approaches widely used are: microextraction in a packed syringe that uses a sorbent at the top of a syringe needle and dispersive solid phase microextraction (DSPME) that uses a minimum amount of sorbent inside the sample and shaking for some time
Membrane based extraction Use of membranes in order to allow selective passage of analytes or matrix compounds across it. Different device and fundamentals can be used, e.g., pervaporation (volatile substances present in a heated donor phase placed inside a pervaporation module evaporate through a porous membrane and the vapor condenses on surface of a cool acceptor stream on the other side of the membrane) or the semipermeable membrane device (SPMD)

Sonication is usually used as pretreatment of environmental and biological samples for the extraction of nonvolatile and semivolatile organic compounds. When comparing the different procedures available for analyte extraction, sonication is considered as a greener and effective method since unsophisticated instrumentation is used and solid–liquid separations can usually be performed in a short time using diluted reagents, small volumes and low temperatures (safer procedures). Most of applications of UAE have been carried out for organic compounds, but the usefulness of ultrasound for element extraction has also been exploited. Ultrasonic extraction of total elements with a diluted acid, speciation with a suitable extractant and selective extraction for evaluation of mobility and bioavailability of different elements has been proposed. Some examples of solid–liquid extraction with the use of ultrasound are shown in Table 3 . 9, 12–27

Table 3 . Some selected applications of ultrasound-assisted extraction for solid samples

Sample Analyte Extractant Sonication system Ultrasound time (min) References
Extraction of organic compounds
Nuts Aflatoxins 80% v/v acetonitrile Bath 10 12
Marine sediments Humic substances 0.5 M NaOH Bath 30 13
Roots Anthraquinones 50% v/v ethanol Bath 60 14
Raspberries Anthocyanins 50% v/v ethanol Probe 3.3 15
Bakery products Fatty acids n-hexane Probe 6 16
Mycobacterial cells Adenosine, guanosine, uridine Chloroform Probe or cup horn 3 17
Extraction of trace elements
Legumes and dried fruits Cd 2–3 M HNO3 Bath 1–2.5 18
Sediments Pb, Cu, Zn, Ni, Mn HNO3, HClO4 and HCl Bath 25 19
Airbone particulate matter Cd, Fe, Pb, Zn HNO3 and HCl Bath 30 20
Fish and shellfish As, Se, Ni, V 0.5%–3% v/v HNO3 Probe 3 21
Dust sediment Cu, Pb, Zn 2 M HNO3 Probe 5 22
Sewage sludge Cd, Cu, Co, Cr, Mn, Pb, Zn HNO3 and HCl Probe 20 23
Biological and environmental samples Cd, Pb, Mn, Ni, Cr Different mixtures of HNO3, H2O2, HCl and HF Cup horn 3–15 9
Extraction for speciation analysis
Fish and shellfish CH3Hg, Hg 2 + , Hg total KOH or TMAH in MeOH Bath 5–90 24
Mussel tissue CH3Hg, Hg total 2 M HCl and 5 M HCl Probe 5 25
Extraction for sequential analysis
Sewage sludge Cd, Cr, Cu, Ni, Pb, Zn Step: (1) 0.11 M CH3COOH; (2) 0.5 M NH2OH·HCl; (3) 30% w/v H2O2, 1 M CH3COONH4 and aqua regia Bath Total: 90 26
Sediment Cd, Cr, Cu, Ni, Pb, Zn Step: (1) 0.11 M CH3COOH; (2) 0.5 M NH2OH; (3) H2O2, 1 M CH3COONH4 Probe Total: 27 27

Specific optimization of the variables influencing ultrasound-assisted extraction processes is usually performed: sonication time, vibrational amplitude (horns), extraction solvent, particle size and solid concentration in the liquid. In general, solvents used are acid solutions or organic solvents with low viscosity and surface tension since these factors hinder the cavitation. The presence of an acidic media is an important prerequisite for quantitative extraction of element. Nitric acid at low concentration (e.g., 3%–5% v/v) is usually chosen for extraction of elements from solid samples when a probe is used, although it depends greatly on the nature of the matrix and the element. Nevertheless, incomplete extraction has been observed from samples containing a typical inorganic matrix (e.g., sediment). It is believed that this finding is related to the ability of ultrasound to penetrate the solid material. Thus, strongly bound analytes should be more difficult to extract, thereby requiring more stringent extraction conditions. A relationship between extractability and binding characteristics of elements in the sample is yet to be established.

The extraction efficiency obtained with ultrasound could be increased by addition of glass beads which promote particle disruption by focusing the energy released by cavitation, and by physical crushing. The use of a bubbling gas during sonication gives rise to an enhanced formation of H2O2 and hydroxyl radicals (OH) thus aiding analyte extraction from oxidizable materials. In general, the use of probe-type sonicators at the appropriate vibrational amplitude and sonication time is required so that extraction efficiency can be improved for strongly-bound elements.

Although most of methods based on UAE have been developed in batch, several continuous procedures have been implemented. To this end, ultrasonic baths or probes are included in flow systems. More frequently, sample is placed in an extraction cell or chamber and then extractant flows through it. This system is immersed in an ultrasound bath or even in a bath with a dipped probe (indirect sonication). Alternatively, a probe can be introduced in an ultrasonic flow cell, the mixture of sample and extractant flowing through it (direct sonication).

Analysis of Marine Samples in Search of Bioactive Compounds

K. Duarte, . Armando C. Duarte, in Comprehensive Analytical Chemistry , 2014

4.1.3 Ultrasound Assisted Extraction (UAE)

Ultrasound assisted extraction (UAE) is also used in the search for bioactive compounds from marine sources and it is based on the effects of acoustic cavitation. The propagation of ultrasonic waves provides a greater solvent penetration into the sample matrix, increasing the contact between the sample and the solvent (or reagent) and improving the mass transfer rates. In addition, this technique is also useful for the extraction of compounds from living organisms since it promotes the breaking of biological cell walls. This technique allows performing simultaneous extractions, the use of low quantities of solvent, the reduction of working times, and the increase in yield and quality of extract. Moreover, UAE is also inexpensive, fast, and versatile compared to traditional techniques, since it can use several solvents of different polarities. However, UAE has some drawbacks, including difficulties in combination with other instruments and automation [5,37] . Oh et al. [18] compared the extraction of polysaccharides from microalgae Spirulina maxima and found that the extraction yield of UAE is improved at least from 25 to 30% in comparison to extraction with hot water or 80% ethanol using traditional extraction processes. Oh et al. [18] also found that the ultrasonic frequency is more effective at improving extraction yields than extraction time, in order to obtain S. maxima extracts, which are most important due to their anticancer activity. In this way, UAE also provides extracts with lower cytotoxicity than conventional solvent and hydrothermal extraction methodologies.

A nutraceutical carotenoid, astaxanthin, was extracted from Haematococcus pluvialis using the UAE technique by Zou et al. [19] . The UAE was performed at 41 °C, for a period of 16 minutes using a mixture of 48% ethanol and 52% ethyl acetate as solvent (optimal conditions) and a liquid-to-solid ratio of 20:1 mL/g, under ultrasound irradiation of 200 W ( Table 4.1 ). The extraction yield of astaxanthin under such conditions was estimated at 27.58 ± 0.40 mg/g. A response surface methodology, based on a Box-Behnken experimental design, was used to optimize the effects of several experimental parameters such as extraction solvent, extraction temperature, and extraction time, on the extraction efficiency of astaxanthin from H. pluvialis. Zou et al. [19] have found that all experimental parameters, both in linear and quadratic terms, exhibit a significant effect on the yield of astaxanthin (p [16] also performed a comparative study of the ability of two extraction methods, PLE and UAE, in the extraction of bioactive compounds (carotenoids) from Chlorella vulgaris. In the PLE experiments, the optimal conditions of temperature and pressures were, respectively, 200 °C and 10.3 MPa, for a period of 20 minutes, using water as solvent, and the UAE was carried out at 25 °C for 25 minutes with ethanol. The results obtained by Plaza et al. [16] suggest that PLE is more efficient than UAE, providing higher yield extraction (39.1 g per 100 g of dry weight) than UAE (extraction yield of 4.79 g per 100 g of dry weight). On the other hand, the authors suggest that PLE is more amenable to control and automation, thus becoming a faster technique.

Combination of Water-Based Extraction Technologies

Noelia Flórez-Fernández, . Herminia Domínguez González, in Water Extraction of Bioactive Compounds , 2017

4.4 Ultrasound and Microwave–Assisted Extraction

The simultaneous application of ultrasound and microwave–assisted extraction is one of the most promising hybrid techniques for fast, efficient extractions because double irradiation can bring additive or even synergic effects. The combination of the two treatments could dramatically improve the release of soluble compounds from plant matrices by disrupting the cell walls, enhancing the mass transfer and facilitating the solvent access to the intracellular compartments, an advantage related to the cavitation phenomenon of ultrasound and the internal heating of microwave ( Leonelli and Mason, 2010 ). Although most combined uses refer to extraction with nonaqueous or with alcoholic solvents ( Cravotto et al., 2008; Hu et al., 2008; Huang et al., 2008; Barrera Vázquez et al., 2014 ), aqueous extraction results also benefited ( Table 17.4 ). Simultaneous application was proposed for the extraction of jujube pectin ( Bai et al., 2015 ) and inulin and a phenols-rich dietary fiber powder from Burdock roots in significantly shorter extraction time than conventional extraction ( Lou et al., 2009; Zhu et al., 2016 ). The process was highly influenced by the microwave power and the solvent to solid ratio. The microscopic observation confirmed the presence of microfractures and disruption of cell walls ( Lou et al., 2009 ). The yield and purity of polysaccharides from Inonotus obliquus obtained with ultrasonic and microwave–assisted extraction were superior to those from traditional hot water extraction ( Chen et al., 2010 ). Sequential combination of ultrasound and microwave extraction was tried for phenolics and iridoids from Fructus corni ( Liu et al., 2011b ) and could potentially minimize or prevent the degradation of pomelo peel extract. This approach provided the highest yield of pectin and galacturonic acid content than adopting the microwave ultrasound and the individual techniques ( Liew et al., 2016 ). Similarly, ultrasound was used as a pretreatment step for microwave extraction of grapefruit pectin ( Bagherian et al., 2011 ). However, despite the beneficial effect of individual assistance of microwaves or ultrasound on alkaline extraction of peanut proteins, yields, purities, and some functional properties, the sequential use of both technologies did not result in a synergistic effect in protein extraction ( Ochoa-Rivas et al., 2017 ). The application of different physical pretreatments before the enzymatic aided oil extraction improved both yield, because of the cell wall disruption and the facilitated deemulsification, and quality, because of the presence of other bioactives in the oil ( Yusoff et al., 2015 ). Sequential application of ultrasound and enzyme–assisted extraction proved suitable. Almost, quantitative extraction of oil from watermelon kernels was achieved when the enzyme treatment with proteases was applied to the previously ultrasound-irradiated material ( Sui et al., 2011; Liu et al., 2011b ) or to microwave-dried material subjected to ultrasound-assisted aqueous extraction of oil, β-carotene, and lycopene from gac aril ( Kha et al., 2015 ).

Table 17.4 . Some Examples of Combined Ultrasound and Microwave–Assisted Extraction of Plant Components

Material (Solute) Conditions Benefits References
Arctium lappa root (inulin, phenolics) 15 mL/g
MW-US: 50 W, 40 kHz
Higher yield and shorter time than conventional process Lou et al. (2009)
Citrus paradisi peels (pectin) 29 mL/g
US: pH 1.8, 27.5 min
MW: 643.4 W, 6.4 min
Higher extraction yield than conventional extraction Liew et al. (2016)
Inonotus obliquus (polysaccharides) 20 mL/g; 19 min
MW: 90 W
US: 50 W
Higher extraction yield than conventional extraction Chen et al. (2010)
Ziziphus jujuba (pectin) 10.03 mL/g
US: 17.66 min
MW: 52.73 s
Bai et al. (2015)
Momordica cochinchinensis (oil, beta-carotene, lycopene) MW drying
US: 9 mL/g, 32 W/g, 20 min
Higher extraction yield than each technique alone Kha et al. (2015)
Zingiber officinale press cake (essential oil, gingerols, and 6-shogaol) MHG: 1.6 W/g
US: 25 mL/g, 0.303 W/cm 3 , 90 min
Total valorization of components Jacotet-Navarro et al. (2016)

MHG, microwave hydrodiffusion and gravity processing; MW, microwave; US, ultrasound.

Other possible combinations and the application of the proposed techniques in multistage processes have been tried. A sequence consisting of the microwave hydrogravity and hot subcritical water processing or alternatively enzyme hydrolysis were useful to extract phenolic compounds from Sargassum muticum in shorter times than conventional processes. Despite the fact that the yield was lower than with conventional solvent extraction, the phenolic content of the extracts and their antiradical properties were enhanced ( Pérez et al., 2014 ). Parada et al. (2015) reported a multistage process consisting on microwave hydrogravity, supercritical CO2 extraction, and the remaining raffinates were subjected either to enzyme-assisted extraction or subcritical water to obtain the soluble fraction of Hericium erinaceus. Sequential application of microwave hydrogravity processing of ginger press cake to recover essential oil and further ultrasound-assisted extraction to obtain gingerols and 6-shogaol from the solid by using constituent water as solvent allowed increased yields over conventional maceration ( Jacotet-Navarro et al., 2016 ). These technologies and combinations have been claimed in different patents; a summarized survey is presented in Table 17.5 .

Table 17.5 . Some Examples of Combined Ultrasound and Microwave–Assisted Extraction of Bioactives

Raw Material Product Technology Steps Advantages References
Biological material Volatiles MAE 25 + 54 + 56 Visinoni et al. (2004)
Solid material Chemical compounds UAE 2; 6 Bates et al. (2006)
Chinese figwort Polysaccharide EAE + MAE 9 + 35 + 25 + 46 + 45 + 47 + 52 + 37 + 60 2; 12 Zhang et al. (2015)
Cinnamon Cinnamon aqueous extract SD 4 + 7 + 11 + 33 + 54 2; 16; 17 He et al. (2015)
Coffee grounds Fatty oils MAE 25 + 56 + 43 + 52 Non declared, 2015
Asian clam Sober-up MAE + EAE 4 + 16 + 25 + 43 + 18 + 19 + 35 + 25 + 43 2; 8; 13; 20 Zhu et al. (2014)
Biological materials Lower the amount of furocoumarins in the preparation of essential oil MHG 25 + 55 Chemat et al. (2007) and Chemat and Vian (2010)
Chrysanthemum Essential oil UAE + SFME 6 + 7 + 11 + 23 + 25 + 56 2; 3; 10; 11; 14 Miao et al. (2015)
Traditional Chinese medicinal plant Flavonoids MAE 1 + 25 + 43 + 48 + 37 + 46 + 59 2; 6 Chen et al. (2014)
Dogwood Saponins UAE + MAE 10 + 29 + 47 + 51 + 59 2; 5; 6; 10; 14 Kang et al. (2014)
Medicinal materials Oleuropein rp UAE 1 + 24 + 48 + 53 1; 4; 6; 16; 17; 20 Chen et al. (2015)
Edible fungus Polysaccharide EAE + MAE 11 + 19 + 16 + 22 + 35 + 25 + 56 + 43 + 51 + 42 Han et al. (2014)
Fritillaria bulb Polysaccharide UAE 14 + 7 + 11 + 23 + 43 + 37 2; 6 Zheng et al. (2013)
Gingko leaves Thermally labile compounds, such as bilobalides PWE 1 Wai and Lang (2000)
Gut weed Polysaccharides MAE 15 + 7 + 9 + 5 + 13 + 16 + 25 + 46 + 51 + 37 + 46 + 60 1; 2; 9; 15; 16; 17; 20 Li et al. (2015b)
Honeysuckle, red peony root, and male fern rhizome Paeoniflorin UAE 10 + 16 + 23 + 43 + 37 + 43 + 54 + 61 Qiang et al. (2006)
Lappaconitine UAE 1 + 23 + 18 + 53 1; 2; 6; 15; 16; 17; 19; 20 Junyi et al. (2012)
Hamamelis Tannins and polyphenols HWE 10 + 21 + 31 + 51 + 56 + 58 Dubois (2004)
Hawthorn and tea leaves Hawthorn tea MAE 4 + 10 + 18 + 25 + 43 Kong et al. (2011)
Lobe and petal Color extraction MAE 6, 2, 15 Lai et al. (2014)
Plant oil, crude protein and fiber UAE 4 + 8 + 11 + 16 + 23 + 46 Lanqin et al. (2005, 2008)
Chinese medicine residue Pectin WSD 19 + 46 + 25 + 16 + 43 3; 16; 11 Li et al. (2013)
Herbage plant Polysaccharide MAE 11 + 16 + 22 + 25 + 56 + 43 + 42 + 43 2; 6; 9; 11; 15; 16 Han et al. (2013)
Plant embryos or seeds rich in DNA and RNA Nucleic acid-rich aqueous extract EAE 18 + 35 + 39 Lubrano et al. (2003)
Plant v-MAE 30 + 45 + 25 2 Mou et al. (2013)
Plant material Essential oil, polyphenol, anthocyanin or protein mixture UAE + MAE 9 + 16 + 29 + 56 + 43/59/46/60 Patrascu et al. (2016)
Lemon peel Essential oil MAE 4 + 7 + 11 + 16 + 25 + 54 1; 5; 11; 12 15; 16 17; 19 Wei and Zheng (2014)
Longan and litchi Polysaccharide UAE 23 + 54 + 42/37 + 43 + 57 2; 3; 5; 16; 20 Zhao (2006)
Medicinal herbs Pharmacologically active constituents SWE Davison and Wheatley (2009)
Medicinal plants Pharmacologically active constituents SWE 32 + 59 Wheatley and Davison (2010)
Medicinal plants Pharmacologically active constituents SWE 10 + 32 + 59 Wheatley and Davison (2011)
Nitraria Polysaccharide MAE 1 + 25 Bi et al. (2015)
Oil bearing plants Oil MAE 10 + 16 + 25 + 46 + 44 Dong (2014)
Plant SWE 7; 17; 19 Zheng et al. (2012)
Rose Essential oil MAE 5 + 27 + 36 1; 2; 16 Wang et al. (2015a,b)
Savin Essential oil WD 1; 6; 16 Wang et al. (2009)
Tea Protein MAE 1 + 25 + 43 + 48 + 38 + 46 + 59 2; 5; 6 Chen (2014)
Tea Polyphenol v-MAE, EAE 4 + 11 + 19 + 28 + 35 + 46 + 47 + 52 + 60 2; 6; 12; 13; 17; 16; 19 Jin (2014)
Tea seeds Tea oil UAE 2 + 5 + 8 + 11 + 13 + 16 + 23 + 39 + 49 1; 6; 8; 16 Zhien et al. (2011)
Tea seeds Oil UAE + EAE 3 + 7 + 11 + 16 + 17 + 23 + 18 + 19 + 35 + 46 + 39 + 50 1; 6; 16; 17; 20 Zhou (2012)
Whole plant or part of a plant Plant extract MAE 26 + 54 Chemat et al. (2011)

Steps: 1: Herb pretreatment; 2: Harvesting; 3: Hulling; 4: Removing impurities/cleaning; 5: Sorting/screening; 6: Refrigerating; 7: Drying; 8: Shelling; 9: Grinding; 10: Cutting/reduction of particle size; 11: Crushing/shattering; 12: Sieving; 13: Weighing; 14: Degreasing; 15: Bleaching; 16: Adding/mixing with/dipping in solvent (water); 17: Heating to enzyme deactivation; 18: Adjusting pH; 19: Adding enzymes; 20: Soaking; 21: Macerating; 22: Stirring; 23: Ultrasound-assisted extraction; 24: Reduced-pressure ultrasound-assisted extraction; 25: Microwave-assisted extraction; 26: Microwave distillation; 27: Microwave hot air deenzyming drying; 28: Vacuum microwave; 29: Ultrasound and microwave–assisted extraction; 30: Water extraction; 31: Boiling; 32: Subcritical water extraction; 33: Steam distillation; 34: Leaching; 35: Enzyme hydrolysis; 36: Extraction by an eddy flow condensation method; 37: Alcohol precipitation; 38: Acidic precipitation; 39: Separation; 40: Liquid/solid separation; 41: Chromatographic elution; 42: Flocculation/precipitation; 43: Filtration; 44: Washing with water; 45: Vaccum/vacuum breaking; 46: Centrifugation; 47: Resin adsorption; 48: Decolorization; 49: Evaporating; 50: Vacuum drying; 51: Concentration; 52: Vacuum/reduced pressure concentration/distillation; 53: Crystallization/recrystallization; 54: Condensing; 55: Collecting by gravity and condensation; 56: Cooling; 57: Freezing; 58: Adding solubilizing and stabilizing agent; 59: Removing water/drying; 60: Freeze-drying; 61: Spray drying.

Advantages: 1: Easy/simple operation; 2: Reduced extraction time; 3: Reduced temperature; 4: Mild reaction conditions; 5: High recovery rate; 6: High yield/efficiency; 7: Selective extraction of products with different polarities; 8: Full utilization of raw material; 9: Small solvent amount; 10: Improved extraction ratio; 11: High quality; 12: High purity; 13: High bioactivity; 14: Small damage to molecular structure; 15: Save energy; 16: Low cost operation/investment; 17: Organic solvents and/or pollution free/low toxicity; 18: Acid solvent free; 19: Environmental friendly; 20: Suitable for industrialization.

EAE, enzyme-assisted extraction; HWE, hot water extraction; MHG, microwave hydrodiffusion; PWE, pressurized water extraction; rpUAE, reduced-pressure ultrasound-assisted extraction; SD, steam distillation; SFME, solvent-free microwave-assisted extraction; v-MAE, vacuum microwave–assisted extraction; WD, Water distillation; WSD, Water steam distillation with duplex effects.

Fundamentals of Ultrasound-Assisted Extraction

Isela Lavilla, Carlos Bendicho, in Water Extraction of Bioactive Compounds , 2017

Abstract

This chapter is mainly concerned with the fundamentals of ultrasound-assisted extraction (UAE) of bioactive compounds using aqueous solutions. In special, the phenomenon of cavitation in heterogeneous media is addressed. Main advantages and drawbacks of ultrasonic systems used for extraction (essentially, baths and probes) are established. Parameters that influence UAE, e.g., sonication time, sonication amplitude, solvent, particle size, solid/liquid ratio, are discussed. A comparison of ultrasound-assisted extraction with other techniques commonly used for extraction of bioactive compounds, both classical and modern, can be found in this chapter. A number of selected applications using different aqueous solutions are also discussed.

Pharmaceutical Analysis | Sample Preparation☆

Ultrasonic Extraction (USE) 42,54,76–78

Ultrasonic extraction (USE), also called ultrasound-assisted extraction (UAE), is a conventional technique for the preparation of solid samples, such as plant-derived medicines. The ability of ultrasound to enhance the efficiency of extraction of organic compounds has been attributed to the phenomenon of cavitation produced in the solvent by the passage of an ultrasonic wave. Several extraction parameters should be optimized, including the polarity and amount of extraction solvent, the mass and type of sample, extraction temperature and time, and the ultrasound source (frequency and intensity). The most important parameters affecting extraction efficiency are extraction solvent and its mixing ratio with water, extraction temperature and time. Although methanol and ethanol are the usual extraction solvents, the optimal solvent depends on the chemical form of the target organic compounds. In general, extraction efficiency is optimized using solvents containing 10%–50% water. The use of high temperatures in USE can increase the efficiency of the extraction process due to an increase in the number of cavitation bubbles. The volume of water required for maximum extraction efficiency may require adjustment, depending on the type and characteristics of individual samples. USE has been widely used, not only for the inexpensive and effective extraction of active components from solid plant matrices, but in combination with pressurized liquid extraction (PLE).

Green Extraction Techniques

Ciara McDonnell, Brijesh K. Tiwari, in Comprehensive Analytical Chemistry , 2017

Abstract

The objective of this chapter is to outline various applications of ultrasound-assisted extraction of bioactive compounds using clean and green solvents. Ultrasound-assisted extraction (UAE) has shown potential to extract range of bioactives from a range of matrices. Compared with conventional extraction techniques, UEA enhances a possibility to improve extraction yields while reducing the use of solvents, providing the opportunity to use greener alternative solvents and enhancing extraction of heat-sensitive components. Factors affecting extraction yields and effect of various extrinsic and intrinsic control parameters of UAE are also discussed. Various advantages, disadvantages and challenges encountered in employing ultrasound for extraction purposes are also outlined.

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