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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 ...

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                   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
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...American journal of biochemistry and biotechnology issn science publications a review on supercritical fluid extraction as new analytical method abbas k mohamed s abdulamir h abas department food technology faculty university putra malaysia upm english arts imam al sadiq iraq abstract this study summarized the sfe advantage disadvantage co sc well special applications in processing such removal fat from enrichment vitamin e natural sources alcohol wine beer encapsulation liquids for engineering solid products characterization functional compounds were also highlighted covered application safety rapid analysis content pesticides foods recent particle formation nan ssupercritical drying outcome finding confirmed that was found to be advance fast reliable clean cheap methods routine key words features introduction temperature especially vicinity critical point small isothermal raise pressure increases is used large scale density remarkably while effect diminishes some grade essential oils...

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