Extraction processes using ultrasound

Acetonitrile, acetone, ethanol, and methanol have been used to extract isoflavones from soy foods. Among them, acetonitrile proved to be the most efficient (Griffith et al., 2001 Murphy et al., 2002). The solvent is supplemented with 0.1 M HC1 to completely un ionize the isoflavones and to release them from protein complexes by denaturing and precipitating the proteins. Room temperature is recommended for extraction to avoid alteration of the natural forms of the isoflavones. The time for extraction, 2 hr, was chosen for maximum recovery and shortest processing time. Ultrasound is used to aid the extraction process by degrading and weakening the cellular matrix. 

The classical techniques for the solvent extraction of materials from vegetable sources are based upon the correct choice of solvent coupled with the use of heat and/or agitation. The extraction of organic compounds contained within the body of plants and seeds by a solvent is significantly improved by the use of power ultrasound. The mechanical effects of ultrasound provide a greater penetration of solvent into cellular materials and improves mass transfer. There is an additional benefit for the use of power ultrasound in extractive processes which derives from... 

The UAE technique is based on the employment of the energy derived from ultrasounds that facilitate the extraction of analytes from the solid sample by the organic solvent [66]. The enhancement of extraction efficiency of organic compounds by UAE is attributed to the phenomenon of cavitation produced in the solvent by the passage of ultrasonic waves [67]. The uses of higher temperatures in UAE lead to an increase in the efficiency of the extraction process [67-69]. The ultrasound-assisted extraction of capsaicinoids from pepper has also been carried out by Barbero et al. in... 

One of the main concerns of the extraction and purification processes are the solvents used, which need to be approved for the use in food industry. During the extraction process, solvents that are not included in the list of approved solvents should not be used." " Also, although the potential use of alternative techniques such as ultrasounds or microwaves is widely discussed, these are not totally accepted due to their unknown health effects, as well as their operational costs. Therefore, the traditional methods prevail until the legal authorities guarantee that all the safety requirements of these new methodologies are accomplished, and until these methodologies become economically viable solutions for the industry. 

Plant material extraction using ultrasound technique in a laboratory scale has been widely used. Review papers were published dealing with the extraction of plant origin metabolites [27, 28], food flavonoids with different solvents [29, 28] and bioactives from herbs [30, 28]. The ultrasonic technology in food processing has attracted widely attentions nowadays [31] and also many papers had described the ultrasonic extraction of flavonoids from citrus peel [31,32,33],... 

The application of ultrasound energy or sonication for process enhancement of bioactive molecules or compounds from plant material is widely published (Saliova et al., 1997 Vinatoru et al., 1997 Vinatoru, 2001 Bruni et al., 2002 Melecchi et al., 2002 Albu et al., 2004 Schinor et al., 2004 Wang and Weller, 2006). A fairly recent review has summarized the scope of ultrasonic-assisted extractions (ViUchu et al., 2008). Part of the attraction of ultrasound for extraction processes is that it is a relatively simple and inexpensive method which can be conducted at ambient temperatures using any particular solvent (Ashokkumar et al., 2008). 

Speckle shearing interferometry, or shearography, is a full field optical inspection teclmique that may be used for the nondestructive detection of surface and, sometimes, subsurface defects. Whilst being more sensitive in the detection of surface defects, it may also be considered for pipe inspection and the monitoring of internal conoslon. In contrast, laser ultrasound and other forms of ultrasound, are point by point measurement techniques, so that scanning facilities and significant data processing is required before information on local defects is extracted from any examination of extensive areas [1 - 3]. 

In the main, the original extractive alkylation procedures of the late 1960s, which used stoichiometric amounts of the quaternary ammonium salt, have now been superseded by solid-liquid phase-transfer catalytic processes [e.g. 9-13]. Combined soliddiquid phase-transfer catalysis and microwave irradiation [e.g. 14-17], or ultrasound [13], reduces reaction times while retaining the high yields. Polymer-supported catalysts have also been used [e.g. 18] and it has been noted that not only are such reactions slower but the order in which the reagents are added is important in order to promote diffusion into the polymer. 

Ultrasound-assisted extraction provides efficient extraction in a shorter processing time than is needed for conventional extraction. The aid of ultrasound will result in a higher extraction yield and reduce solvent consumption. The extract may exhibit a wide range of colors (pale yellow, brown, red). For anthocyanin extraction in an acidic environment, the extract will be deep red, pink, or purple. The extract may contain considerable amounts of lipophilic compounds (e.g., chlorophyll, carotenoids, lipids). Prior to solid-phase extraction, those compounds can be eliminated from the extracts using liquid-liquid extraction. 

Ultrasound-assisted extraction (USE) is an effective method for leaching many analytes from different kinds of samples [52-55]. It is simple, fast, efficient, and inexpensive in comparison with conventional extraction techniques such as solvent extraction in the Soxhlet apparatus. Ultrasound-assisted solid-liquid extraction is an effective and time-saving extraction method. Sonication accelerates the mass-transfer process between two phases. Use of ultrasound results in a reduction in operating temperature, allowing the extraction of temperature-sensitive components. The ultrasound apparatus is cheaper and its operation is easier in comparison with other novel extraction techniques such as MAE. 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

As stated above, the use of ultrasound as auxiliary energy for leaching has been widely exploited for the extraction of a variety of analytes from different types of solid samples. While ultrasonic irradiation has been advantageously used over other methods to accelerate manual leaching of solid samples, this type of energy has scarcely been employed for pretreatment in continuous systems, even though it expedites the sampling process considerably. 

The isolation of the effective compositions from some traditional Chinese herbs under influence of ultrasound was reported [71], The compounds Helicid (4-for-mylphenyl-allopyranoside), Berberin Hydrochloride, and Bergenin could each be isolated from different plant materials using ethanol at room temperature under the influence of sonication. Ultrasonic irradiation reduced the temperature and time required for the process, thereby increasing the efficiency of extraction. The products contained fewer impurities and the ultrasonic process appeared to involve simpler technology. 

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