Supercritical fluid extraction in herbal and natural product studies — a practical review

Department of Chemistry, University of Idaho, Moscow, ID 83844-2343, USA
Talanta (Impact Factor: 3.5). 02/2001; DOI: 10.1016/S0039-9140(00)00557-9

ABSTRACT Due to increasingly stringent environmental regulations, supercritical fluid extraction (SFE) has gained wide acceptance in recent years as an alternative to conventional solvent extraction for separation of organic compounds in many analytical and industrial processes. In the past decade, SFE has been applied successfully to the extraction of a variety of organic compounds from herbs and other plants. This review article presents the practical aspects of SFE applications in sample preparation, selection of modifiers, collection methods, on-line coupling techniques, means for avoiding mechanical problems, and approaches to optimization of SFE conditions. SFE can also be used to clean up pesticides from herb medicines. SFE processes can be modeled to acquire useful information for better understanding of the extraction, mechanisms and optimization of the extraction procedures. With increasing public interest in natural products, SFE may become a standard extraction technique for studying herbal, food and agricultural samples.

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    ABSTRACT: Supercritical fluid extraction (SFE) is a recent technology that is based on the solvent power that some fluids exhibit under pressure and temperature above certain values named as critical point. This process, using supercritical CO 2 as solvent, has gained wide acceptance in the last years, because of its advantages compared to conventional solvent extraction ones. Nevertheless one of the difficulties of SFE is to achieve favourable kinetics due to the fact that mechanical stirring is not easily applied to an extractor vessel operating at high pressures. An interesting alternative is the use of power ultrasound (HPU). Ultrasonic radiation represents an efficient way to enhance mass transfer processes, because of mechanisms such as acoustic streaming, turbulence, radiation pressure, compressions and decompressions in the material, heat and/or cavitation.
    41º Congreso Nacional de Acústica, Tecniacústica 2010; 01/2010
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    ABSTRACT: The use of hot compressed water in both its sub-and super-critical regions embraces a range of reduced temperatures (T r) and pressures (P r) depending on the unit processing result that is desired. Solute solubility enhancements in sub-critical water can be estimated a priori by several empirical cubic equations correlating solute solubility with temperature. These include the well known Clifford relationship which predicts solubility enhancements of 10 2 – 10 6 or greater depending on the properties of solute moieties being extracted in sub-critical water. We have also utilized solution thermodynamic data such as solute solubility data, Henry Law constants, and partition coefficients in aqueous media at ambient conditions to predict the increase in solubility under sub-critical water conditions. The recent compendium of aqueous solubility data of Yalkowsky and He at ambient conditions can be used with the above relationship and other predictive equations. Fundamental mass transfer data; such solute diffusivities, mass transfer coefficients, and fluid linear velocity should be optimized to achieve high solute flux rates in the case of sub-critical water extraction (SWE). Solute diffusion in sub-H 2 O increases over ten-fold relative to ambient diffusivities and similarly, k pi , the overall mass transfer coefficient increases with temperature in the sub-H 2 O region. Experimental data show that an accurate mass balance of all of the components in sub-critical water process requires differential equations formulated to account for the extraction of the target solutes -as well as their conversion (degradation) – as a function of temperature and processing time. Preliminary evidence from degradation rate constants suggests that components in the sample matrix synergistically-interact to reduce loss of the sub-critical water-extracted solutes due to thermally-induced degradation. From a practical perspective, the simultaneous occurrence of both extraction and reaction modes during sub-critical water processing predicts that there is an optimal extraction time to achieve SWE and minimize degradation of the target solutes, unless conversion to another end product is desired. Experiments in the sub-H 2 O processing of milk thistle verify this as well as the importance of conducting extractions at the lowest temperature possible and/or optimizing the sub-H 2 O velocity through the processing vessel to avoid solute degradation. Hence in the case of SWE, the suppression of the rate constant for solute degradation, k d , is opposite for the case of sub-critical water reaction (SWR), where k d is optimized or regulated to give a desired product composition.
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    ABSTRACT: The aim of this study was to compare the effects of solvent and ultrasound-assisted extraction methods with supercritical fluid extraction on antioxidant activity of loquat (Eriobotrya japonica Lindl.) fruit skin extract in stability of soybean oil at 25°C. Oxidative stability alterations of soybean oils containing 400 (SEA) and 1000 ppm (SEB) of ethanol extract, 400 (SSA) and 1000 ppm (SSB) of supercritical CO2 extract, 400 (SUA) and 1000 ppm (SUB) of ultrasound-assisted extract, and 100 ppm of tertiary butylhydroquinone (TBHQ) were monitored by measuring the peroxide value, thiobarbituric acid value, free fatty acids, conjugated dienes and trienes values. Oxidative changes in SEA were lower than that of oils treated with other extracts, but the best protection was observed in soybean oil consisting TBHQ. The solvent extraction method produces the maximum amount of phenolic and tocopherol compounds from loquat fruit skin. Therefore, solvent extraction method had a better effect on antioxidant activity of the loquat fruit skin extract.
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