Vegetable oils, supercritical fluid extraction

E. Reverchon and C. Marrone, Modeling and simulation of the supercritical CO2 extraction of vegetable oils , / Supercrit Fluids, 2001,19,161-75. 

Supercritical fluid extraction (SFE) has been widely used to the extraction processes in pharmaceutical industries. Besides application of SFE in phannaceuticals, it has been applied on a wide spectmm of natural products and food industries such as natural pesticides, antioxidants, vegetable oil, flavors, perfumes and etc [1-2]. 

M.A. Lage Yusti and J.L. Cortizo Davina, Supercritical fluid extraction and high-performance hquid chromatography-fluorescence detection method for polycyclic aromatic hydrocarbons investigation in vegetable oil. Food Cont. 16 (2005) 59-64. 

The promise shown by supercritical fluid extraction led to the development of the Solexol process for the purification and separation of vegetable and fish oils. This process concentrated the polyunsaturated triglycerides in vegetable oils and the so-called vitamin A values from fish oils using propane as a selective solvent [5]. 

Toward this end, we have investigated tandem or coupled processes that embodied the use of pressurized fluids, namely carbon dioxide, for both extraction, fiactionation and reaction. Related exanqrles to the work described here are coupling supercritical fluid extraction (SFE) with production scale supercritical fluid chromatography (SFC) for the enrichment of high value tocopherols from natural botanical sources (/0), or subcritical water hydrolysis of vegetable oils (77) followed 1 partition into dense carbon dioxide to produce industrially-useM mixtures of tty acids. 

In this chapter an environmental friendly extraction process of com germ oil based on the use of supercritical CO2 (SC-CO2) is presented. The effect of important operating parameters in supercritical fluid extraction (SEE) processes such as pressure, temperature and flow rate on the extraction kinetics and the quality of the extracted oil is discussed. As for many SC-CO2 extractions of vegetable oils, extraction curves of com germ oil present an initially linear part with a slope close to the oil solubility value in CO2. Then, a second section of the extraction curve is determined by the diffusional resistance in the solid matrix. Characterization of supercritical cmde com oil is presented by showing some properties reported in the literature such as physical parameters, fatty acid composition, neutral lipids, content of tocopherols, acid index, peroxide value, antioxidant capacity and the oxidative stability. 

Vasapollo G, Longo L, Rescio L and Ciurlia L 2004. Innovative supercritical CO2 extraction of lycopene from tomato in the presence of vegetable oil as co-solvent. J Supercrit Fluids 29(1-2) 87-96. 

The interest in mass transfer in high-pressure systems is related to the extraction of a valuable solute with a compressed gas. This is either a volatile liquid or solid deposited within a porous matrix. The compressed fluid is usually a high-pressure gas, often a supercritical fluid, that is, a gas above its critical state. In this condition the gas density approaches a liquid—like value, so the solubility of the solute in the fluid can be substantially enhanced over its value at low pressure. The retention mechanism of the solute in the solid matrix is only physical (that is, unbound, as with the free moisture), or strongly bound to the solid by some kind of link (as with the so-called bound moisture). Crushed vegetable seeds, for example, have a fraction of free, unbound oil that is readily extracted by the gas, while the rest of the oil is strongly bound to cell walls and structures. This bound solute requires a larger effort to be transferred to the solvent phase. 

A cylindrical extractor, 1-m long, is filled with crushed-vegetable-oil seeds. The oil is to be extracted with pumping supercritical carbon dioxide at a density of 500 kg/m3 through the packed bed. The estimated solubility of the oil in the dense gas at this density is 3.425 kg/m3. The superficial velocity of the carbon dioxide in the bed will be 1 mra/s. This fluid velocity is sufficiently small for the fluid to become saturated with oil. We are required to estimate the minimum time of operation for complete extraction of the oil from the bed. The initial oil fraction is 12% (wt/wt) based on wet seeds, the void fraction of the bed is 40%, and the density of the particles is 900 kg/m3. 

The use of supercritical fluids in extraction processes has become well established. Until now, the extraction of liquids, as for example vitamins or vegetable edible oils, has been carried out in countercurrent columns. Dense gases offer several advantages over conventional solvents such as selective dissolving power, reduced thermal stress of the products or its physiological harmlessness. A supercritical fluid also has a density close to those for liquids, the viscosity is nearly 100 times lower and the diffusivity is up to 100 times higher than those of ordinary liquids as can be seen in table 1. 

Numerous high pressure Hquid chromatographic techniques have been reported for specific sample forms vegetable oils (55,56), animal feeds (57,58), sera (59,60), plasma (61,62), foods (63,64), and tissues (63). Some of the methods require a saponification step to remove fats, to release tocopherols from ceHs, and/or to free tocopherols from their esters. AH require an extraction step to remove the tocopherols from the sample matrix. The methods include both normal and reverse-phase hplc with either uv absorbance or fluorescence detection. Application of supercritical fluid (qv) chromatography has been reported for analysis of tocopherols in marine oHs (65). 

SFE has been used for a relatively long time on a large industrial scale and only recently on a smaller, laboratory scale. There are excellent reviews that cover the entire gamut of SFE applications (3,8). The often cited example is decaffeination of coffee. Other examples of natural products extraction in the food industry include extraction of hops, spices, flavors, and vegetable oils. Table 2 lists selected companies that are involved in supercritical fluid processes for natural products (24). 

Other carotenoids such as lycopene from tomato and its industrial waste [65-68] and lutein esters from marigold (Tagetes erecta) petals [69-71] had been extracted with supercritical fluids, achieving better extractiOT yields when modifiers and cosolvents were used as acetone, chloroform, ethanol, and vegetable oils. 

Reverchon, E., and C. Marrone. 2001. Modeling and Simulation of the Supercritical CO2 Extraction of Vegetable Oils. Journal of Supercritical Fluids 19 (2) 161-175. 

Although a continuous and isobaric operated high-pressure column process seems to be beneficial, no absorption liquid with suitable distribution coefficients is often available. An incomplete purification of the supercritical fluid leads to strongly increased solvent to feed ratios. Thus, the extracted components are separated by pressure reduction or by adsorption like in supercritical processes for solid material. An example is given in Figure 8.18 for the deacidiflcation of vegetable oil [36]. 

The technology of extraction applying supercritical fluids is a viable alternative to conventional methods for extraction of many compounds, among which are vegetable oils, which are a source of a variety of pigments, vitamins, essential fatty acids, and other constituents of high nutritional and functional value that can be preserved more effectively. 

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