127x Filetype PDF File size 0.20 MB Source: thescipub.com
American Journal of Biochemistry and Biotechnology 4 (4): 345-353, 2008 ISSN 1553-3468 © 2008 Science Publications A Review on Supercritical Fluid Extraction as New Analytical Method 1 1 1 2 Abbas, K.A., A. Mohamed, A.S. Abdulamir and H.A. Abas 1Department of Food Technology, Faculty Food Science and Technology, University Putra Malaysia (UPM), Malaysia 2Department of English, Faculty of Arts, University of Imam Al-sadiq, Iraq Abstract: This review study summarized the Supercritical Fluid Extraction (SFE) as new analytical method. The advantage and disadvantage of CO (SC-CO )as well as special applications of SFE in 2 2 food processing such as removal of fat from food, enrichment of vitamin E from natural sources, removal of alcohol from wine and beer, encapsulation of liquids for engineering solid products and extraction and characterization of functional compounds were also highlighted. The study also covered the application of SFE in food safety such as rapid analysis for fat content, rapid analysis for pesticides in foods as well as the recent applications of SFE in food such as supercritical particle formation and nan particle formation and ssupercritical drying. The outcome finding confirmed that SFE was found to be advance, fast, reliable, clean and cheap methods for routine food analysis. Key words: Supercritical fluid, applications, features INTRODUCTION temperature. Especially in the vicinity of the critical point a small isothermal raise in pressure increases the SFE is used on a large scale for the extraction of fluid density remarkably while the effect diminishes some food grade and essential oils and pharmaceutical with increasing distance from the critical values. Thus, products from plants. It is relatively rapid because of the solvent strength of a fluid can be controlled more [1] the low viscosities and high diffusivities associated easily than that of a liquid solvent . Recently, the with supercritical fluids. The extraction can be selective supercritical fluid has approved higher diffusion to some extent by controlling the density of the medium coefficient and lower viscosity and surface tension than and the extracted material is easily recovered by simply a liquid solvent, which leads to a more favorable mass [3] depressurizing, allowing the supercritical fluid to return transfer . to gas phase and evaporate leaving no or little solvent The demand for new analytical techniques in food [1] residues . However, carbon dioxide is the most and environmental sciences is strongly related to the common supercritical solvent. higher demand of information on processing, quality Since the end of the 1970s, supercritical fluids has control, adulteration, contamination, environmental and been used to isolate natural products, but for a long food regulations and the need for faster, more powerful, time the applications concentrated on only few cleaner and cheaper analytical procedures are required products. Now the development of processes and by chemists, regulatory agencies and quality control equipment is beginning to pay off and industries are laboratories to meet these demands can be achieved by getting more and more interested in supercritical SFE. Thus, this review paper has been justified. [2] techniques . In SF the physicochemical properties of a given Properties and fundamentals of supercritical fluids fluid, such as density, diffusivity, dielectric constant Solvent strength: The density of a supercritical fluid is and viscosity can be easily controlled by changing the extremely sensitive to minor changes in temperature pressure or the temperature without ever crossing phase and pressure near the critical point. The densities of the [1] boundaries . The phase diagram of a single substance fluids are closer to that of organic liquids but the can be seen in Fig. 1. solubility of solids can be 3-10 orders of magnitude The dissolving power of a supercritical fluid higher. The solvent strength of a fluid can be expressed depends on its density, which unlike that of liquid by the solubility parameter, which is the square root of solvents is highly adjustable by changing pressure or the cohesive energy density and is defined rigorously Corresponding Author: Abbas, K.A., Department of Food Technology, Faculty Food Science and Technology, University Putra Malaysia (UPM), Malaysia 345 Am. J. Biochem. & Biotech., 4 (4): 345-353, 2008 CO is not a very good solvent for high molecular 2 weight and polar compounds. To increase the solubility of such compounds in supercritical carbon dioxide, small amounts (ranging from 0 to 20 mol %) of polar or non-polar cosolvents called modifiers may be added. The co solvent interacts strongly with the solute and [1,2] significantly increases the solubility . Co-solvents or modifiers: A more common practice in SFE is to change the polarity of the supercritical fluid and increase their solvating power towards the analyte of interest by employing polar modifiers (co-solvents). For example, the addition of relatively small percentages (1-10%) of methanol to carbon dioxide expands its extraction range to include more polar analytes. The modifiers can also reduce the analyte- Fig. 1: Phase diagram for a single substance. P , critical [1] c matrix interactions improving their quantitative pressure; T , critical temperature [1] c extraction . There are two main procedures to study with co- from first principles. A plot of the solubility parameter solvents or modifiers in SFE are; the first one, and the for carbon dioxide versus pressure would resemble that most common, accounts for a mixing of the modifier [3] a plot of density versus pressure . This confirms that with the CO flow while the second mixes the modifier the solvation strength of a supercritical fluid is directly 2 with raw material in the extraction cell. This procedure related to the fluid density. Thus the solubility of a solid is always associated to a static extraction step in which can be manipulated by making slight changes in the modifier, in intimate contact with the sample temperatures and pressures. Another attractive feature matrix, is able to substitute the analyte molecules bound of supercritical fluids is that the properties lie between in active centers of the matrix and release them into the that of gases and liquids. A supercritical fluid has [5] supercritical fluid phase . densities similar to that of liquids, while the viscosities and diffusivities are closer to that of gases. Thus, a Extraction with supercritical fluids: Supercritical supercritical fluid can diffuse faster in a solid matrix extraction has been applied to a large number of solid than a liquid, yet possess a solvent strength to extract matrices. The desired product can be either the extract [4, 2] the solute from the solid matrix . or the extracted solid itself. The advantage of using supercritical fluids in extraction is the ease of Phase behavior: An understanding of the phase separation of the extracted solute from the supercritical behavior is important since the phase behavior observed fluid solvent by simple expansion. In addition, in supercritical fluids considerably differ from the supercritical fluids have liquid like densities but behavior observed in liquids. One such behavior is the superior mass transfer characteristics compared to retrograde region. For an isobaric system, an increase in liquid solvents due to their high diffusion and very low the temperature of a solution increases the solubility of surface tension that enables easy penetration into the the solute over certain ranges of pressure (consistent porous structure of the solid matrix to release the with the typical liquid systems) but decreases the solute [2,6] solute . solubility in other pressure ranges. This anomalous Extraction of soluble species (solutes) from solid behavior wherein the solubility of the solute decreases matrices takes place through four different mechanisms. with a temperature increase is called the retrograde If there are no interactions between the solute and the behavior. Thus, the following generalizations may be solid phase, the process is simple dissolution of the made regarding the solute solubilities in supercritical solute in a suitable solvent that does not dissolve the fluids. Solute solubilities approach and may exceed that [2] solid matrix . If there are interactions between the of liquid solvents. Solubilities generally increase with solid and the solute, then the extraction process is increase in pressure. An increase in the temperature of termed as desorption and the adsorption isotherm of the the supercritical fluid may increase, decrease or have no solute on the solid in presence of the solvent determines effect on the solubility of the solute depending upon the the equilibrium. Most solids extraction processes, such [1] pressure . as activated carbon regeneration, fall in this category. A 346 Am. J. Biochem. & Biotech., 4 (4): 345-353, 2008 third mechanism is swelling of the solid phase by the solvent accompanied by extraction of the entrapped solute through the first two mechanisms, such as extraction of pigments or residual solvents from polymeric matrices. The fourth mechanism is reactive extraction where the insoluble solute reacts with the solvent and the reaction products are soluble hence extractable, such as extraction of lignin from cellulose. Extraction is always followed by another separation process where the extracted solute is separated from the [4] solvent . Another important aspect in supercritical extraction relates to solvent/solute interactions. Normally the Fig. 2: A simplified drawing of a process-scale [1] interactions between the solid and the solute determine supercritical fluid extractor . the ease of extraction, i.e., the strength of the adsorption isotherm is determined by interactions between the the system. The product is then collected via a valve [1,2] adsorbent and the adsorbate. However, when located in the lower part of the separator(s) . supercritical fluids are used, interactions between the solvent and the solute affect the adsorption Advantages and drawbacks of supercritical CO2 characteristics due to large negative partial molar (SC-CO ): There are a large number of compounds that 2 volumes and partial molar enthalpies in supercritical can be used as a fluid in supercritical techniques, but by [4,6] far the most widely used is carbon dioxide. From the fluids . The thermodynamic parameters that govern the viewpoint of pharmaceutical, nutraceutical and food extraction are found to be temperature, pressure, the applications it is a good solvent, because it is non-toxic, adsorption equilibrium constant and the solubility of the non-flammable, inexpensive, easy to remove from the organic in supercritical fluid. Similar to the retrograde product and its critical temperature and pressure are behavior of solubility in supercritical fluids, the relatively low (Tc=31.1°C, pc=72 bar) make it important adsorption equilibrium constants can either decrease or for food and natural products sample preparation, is the increase for an increase in temperature at isobaric ability of SFE using CO to be operated at low 2 conditions. This is primarily due to the large negative temperatures using a non-oxidant medium, which partial molar properties of the supercritical fluids. In allows the extraction of thermally labile or easily addition to the above factors, the rate parameters like oxidized compounds. It is environmental friendly and the external mass transfer resistances, the axial generally recognized as safe by FDA and EFSA. These dispersion in the fluid phase, and the effective diffusion properties make it suitable for extracting, for example, of the organics in the pores also play a crucial role in thermally labile and non-polar bioactive compounds the desorption process. A thorough understanding of but, because of its non-polar nature, it cannot be used these governing parameters is important in the for dissolving polar molecules. The solubility of polar modeling of supercritical fluid extraction process and in compounds and the selectivity of the process can be the design, development and future scale-up of the increased by adding small quantities of other solvents, [4] such as ethanol, in the fluid that named as co-solvent or process . modifier. On one hand, it decreases the processing SFE process: A simplified process-scale SFE system is times, increases yields and makes it possible to use shown in Fig. 2 and a typical batch extraction proceeds milder processing conditions, but on the other, it as follows. Raw material is charged in the extraction complicates system thermodynamics and increases [3] tank which is equipped with temperature controllers capital costs . and pressure valves at both ends to keep desired The use of high purity SFE-grade CO is not 2 extraction conditions. The extraction tank is pressurized required but impurity and moisture in industrial grade with the fluid by means of pumps, which are also CO can accumulate and may interfere with further 2 needed for the circulation of the fluid in the system. analytical operations (gas or liquid chromatography). From the tank the fluid and the solubilized components Thus, an on-line fluid cleanup system may be used to are transferred to the separator where the solvation remove trace contaminants. An important drawback of power of the fluid is decreased by increasing the SC-CO2 and most of the other supercritical fluids is that temperature, or more likely, decreasing the pressure of predominantly, a non-polar extraction fluid, such as 347 Am. J. Biochem. & Biotech., 4 (4): 345-353, 2008 CO, is used. Therefore, a logical trend to widen the Enrichment of vitamin E from natural sources: SFE 2 application range of this technique is the study of new offers several advantages for the enrichment of methods to decrease analyte polarity to make them tocochromanols over conventional techniques such as more soluble in non-polar supercritical fluids. In this vacuum distillation, in particular a lower operating sense, chemical in situ derivatization has been applied temperature. As starting material one can use various to improve the selectivity of the extraction towards a edible oils or their distillates. Most promising as feed specific group of compounds[3,5]. So the solvent power [9] of SC-CO can be summarized by a few rules: materials are CPO) and SODD . CPO contains several 2 tocotrienols and tocopherols at a total concentration of approximately 500ppm. SODD may contain (after • It dissolves non-polar or slightly polar compounds. several conventional concentration steps) about 50% • The solvent power for low molecular weight tocopherols. Both materials can be used for the compounds is high and decreases with increasing [8,9] molecular weight. production of enriched fractions of tocochromanols . • SC-CO has high affinity with oxygenated organic Although it is possible to recover tocochromanols 2 directly from CPO, it is better to produce esters of the compounds of medium molecular weight. triglycerides in order to be able to more easily separate • Free fatty acids and their glycerides exhibit low these compounds from the tocochromanols. In this solubilities. method, the triglycerides are subject to an esterification • Pigments are even less soluble. with methanol to form fatty acid methyl esters, which • Water has a low solubility (<0.5% w/w) at o are easily extractable with CO . That means that the temperatures below 100 C. 2 • Proteins, polysaccharides, sugars and mineral salts tocochromanols, together with other unsaponifiable are insoluble and; matter such as squalene and sterol are enriched in the • SC-CO2 is capable of separating compounds that bottom phase of an extraction column. This attempt is are less volatile, have a higher molecular weight described in more detail by. For a discussion of [2] enriching tocochromanols, phase equilibrium data have and/or are more polar as pressure increases . [10] to be considered first . FFA and tocochromanols Special applications of supercritical fluids to food exhibit a much higher solubility in CO than the 2 processing: As mentioned before carbon dioxide is the triglycerides. Hence, these components are enriched in most common supercritical fluid in the food industry. the gaseous phase, expressed by a distribution Due to the non-toxicity and low critical temperature, it coefficient being higher than one. The distribution can be used to extract thermally labile food components coefficient of the triglycerides is smaller than one, and the product is not contaminated with residual whereas that for the carotenes is much smaller than one, solvent. Further, the extract’s color, composition, odor, meaning that these components stay in the liquid oil texture are controllable and extraction by supercritical phase. Thus, tocochromanols can be extracted as the top fluid carbon dioxide retains the aroma of the product. phase product in a separation column, whereas Supercritical fluid extraction provides a distinct carotenes remain in the bottom phase product together advantage not only in the replacement but also extracts with triglycerides. For recovering the carotenes together oils that are lower in iron and free fatty acid. Some with the tococromanols the above mentioned application of SFE in food is mentioned below: esterification to volatile (CO soluble) methyl esters 2 Removal of fat from foods: Edible oils and their makes possible to recover tocochromanols and components has been the target of supercritical fluid carotenes (together with squalene and sterols) as bottom [9,11] processing since the early 70s. Although product from this natural source .When the triacylglycerides are only fairly soluble in SC-CO , the glycerides (in case of the esterification) or the FFAs 2 from deodorizer distillates have been removed, then advantages of organic solvent-free processing have there is a feed material available for obtaining enriched stimulated research and development in various areas. fractions of tocochromanols and carotenes of much One of these is the removal of fat from food. The higher concentration. In this feed material, process has been fully designed for commercial tocochromanols and carotenes (in case of palm oil) are application, using the aforementioned standard design. the main components and have to be separated from The process has the advantage of producing fat-free or other unsaponifiable substances present, such as fat-reduced potato chips. According to the expected squalene and sterols. Of these compounds, squalene has taste the amount of remaining fat in the potato chips can [7,8] the highest solubility in SC-CO , all phytosterols have a easily be controlled . 348 2
no reviews yet
Please Login to review.