Isolation using supercritical carbon dioxide extraction

Reverchon E, Ambruosi A, Senatore F. Isolation of peppermint oil using supercritical carbon dioxide extraction. Flavour Fragrance J 1994 9 19-23. 

Supercritical fluid extraction (SEE) using supercritical carbon dioxide (SC-CO2) has been successfully used for isolation of volatile nitrosamines from different matrices such as tobacco and food products. This technique presents several advantages with respect to other extraction methods (e.g., mineral oil distillation or low-temperature vacuum distillation) currently used. Thus, SEE minimizes sample handling, provides fairly clean extracts, expedites sample preparation, and reduces the use of environmentally toxic solvents. Good results have also been obtained with the use of SPE in the analysis of food matrices combining extraction with Extrelut sorbent and purification with Florisil. This method is applicable for the analysis of a range of the most widely encountered volatile N-nitrosamines, including the poorly volatile NDBA, NDBzA, and N-nitroso-N-methylaniline in various food products. Active carbon is suitable for this preconcentration step due its low cost, versatility, and easy application. 

Plants and plant extracts have been used as medicine, culinary spice, dye and general cosmetic since ancient times. Plant extracts are seen as a way of meeting the demanding requirements of the modem industry. In the past two decades, much attention has been directed to the use of near critical and supercritical carbon dioxide solvent, particularly in the food pharmaceutical and perfume industries. CO2 is an ideal solvent because it is non-toxic, non-explosive, readily available and easily removed from the extracted products. At present the major industrial-scale applications of supercritical fluid extraction (SFE) are hop extraction, decaffeination of coffee and tea, and isolation of flavours, fragrances and other components from spices, herbs and medicinal plants [1-4]. 

Microcystins are an increasingly important group of bioactive compounds, produced mainly by planktonic cyanobacteria. They are a family of cyclic heptapeptides that cause both acute and chronic toxicity. Purified microcystins are utilized in a range of research applications. This review summarizes the isolation of microcystins from the cyanobacteria by supercritical fluid extraction (SFE). The microcystins can be successfully extracted when a modifier is used in supercritical carbon dioxide fluid. The advantage of the method is that the sample handling steps are minimized, thus reducing possible losses of microcystin and saving extraction and purification time. 

In the present investigation, supercritical carbon dioxide and carbon dioxide -h co-solvent mixtures were used to extract and isolate a model pyrrolizidine alkaloid from its parent plant. Pyrrolizidine alkaloids have been used in herbal medicine to combat tumors as long ago as the fourth century A.D. (4) and to treat cancer since the tenth century A.D. (5). More recently, they have received increasing attention as chemotherapeutic drugs. Processes for their separation, however, are specific to each alkaloid, and either lead to chemical modification of the alkaloid or require the use of solvents which must then be completely removed from the extract. 

The first report on DFA formation in higher plants dates back to 1933, when Schlubach and Knoop [23] isolated a compound tentatively identified as a-D-fructofuranose p-o-fmctofuranose l,2 2,l -dianhydride (10, also known as DFA I) from Jerusalem artichoke. Alliuminoside, a difructofuranose 2,6 6,2 -dianhydride for which configuration at the glycosidic linkages was not determined, was isolated from tubers of Allium sewertzowi [24], However, the fact that these results have not been further confirmed throws some doubt onto whether the DFAs were actually from plant origin or were formed by the presence of microorganisms. The enzymic formation of a-o-fructofuranose p-o-fructofuranose l,2 2,3 -dianhydride (1, DFA HI) in sterilized homogenates of the roots of Lycoris radiata, a plant use in China as a traditional folk medicine, unequivocally demonstrated the capacity of this plant to produce this particular DFA [25]. The compound was further extracted from the intact bulbs by supercritical carbon dioxide and its structure unequivocally established by NMR [26]. 

For sample preparation, isolation and separation traditional methods like distillation (e.g. essential oil content of raw materials) or Soxhlet extraction are still in use. Beyond that, more recent methods are employed, for example supercritical fluid extraction with liquid carbon dioxide. 

Supercritical fluid extraction processes are particularly appropriate for the separation and isolation of biochemicals where thermal decomposition, chemical modification, and physiologically-active solvents are undesirable. Examples of these bioseparations include the extraction of oils from seeds using carbon dioxide (1), of nicotine from tobacco using carbon dioxide-water mixtures (2), and of caffeine from coffee beans again using carbon dioxide-water mixtures (3). 

The use of ion exchange resins combined with supercritical extraction results in an attractive isolation technique. Since the pyrrolizidine alkaloids are generally basic, the process described here could be used for the isolation of other members of this class, and for other basic alkaloids. In designing a process using ion exchange resins, it is important that the co-solvent not deactivate the resin. In our example, water and ethanol are acidic in carbon dioxide and, therefore, do not deactivate the acidic resin. An industrial process based on this concept could be quite efficient and inexpensive since pressure reduction and subsequent solvent recompression are unnecessary (Figure 11). 

The use of critical fluids for the extraction and refining of components in natural products has now been facilitated for over 30 years. Early success in the decaffeination of coffee beans and isolation of specific fractions from hops for flavoring beer, using either supercritical carbon or liquid carbon dioxide, are but two examples of the commercial application of this versatile technology. Critical fluid technology, a term that will be used here to embrace an array of fluids under pressure, has seen new and varied applications which include the areas of engineering-scale processing, analytical, and materials modification. 

A supercritical fluid is defined as any substance that is above its critical temperature and pressure. Supercritical fluids have physical properties intermediate between liquid and gas phases the solvating power (density) of a SE is similar to that of a liquid, and its diffusivity and viscosity are similar to that of a gas. Carbon dioxide (CO2) is the most widely used SE because of its inertness, low cost, high purity, low toxicity, and low critical parameters (CO2 Tc = 31.3°C, Pc = 72.9 atm). If extraction cannot be achieved using CO2, a more polar SE (e.g., N2O or CHE3) can be used. Alternatively, a polar modifier (MeOH, EtOH, or H2O) may be added to the SE in order to increase the solvating power. Several SEE applications have been reported in peer-reviewed literature for selective isolation of residues from food. " The number of published applications has decreased in recent years, which may be... 

The lipid extraction processes commonly used to explore the potential of various oilseeds are hot and cold extraction by hydraulic/mechanical pressing solid-liquid extractions using petroleum ether, hexane, ethanol, methanol, and chloroform among other reagents isolated or combined and extractions using supercritical fluids, such as ethanol, propanol, n-pentane, ammonia, and carbon dioxide (CO )- However, research on the interactions between methods of extraction and their effect on the quality and the thermal and oxidative behavior of these oilseeds has so far been scanty [1-3]. 

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