Simulation and optimization of supercritical fluid purification of phytosterol esters

Supercritical carbon dioxide extraction to separate phytosterol esters from fatty acid esters and tocopherols was simulated and optimized using the group contribution equation of state. Experimental extraction data at 328 K, pressures ranging from 200 to 280 bar and solvent‐to‐feed ratio around 25, was employed to verify the performance of the thermodynamic model. The raw material is the product obtained after a two‐step enzymatic reaction carried out on soybean oil deodorizer distillates, and contains mainly fatty‐acid ethyl esters, tocopherols and phytosterol esters. The extraction process was simulated using model substances to represent the complex multicomponent feed material. Nonlinear programming techniques were applied to find out optimal process conditions for a steady‐state countercurrent process with partial reflux of the extract. The process optimization procedure predicts that a product with 94.2 wt % of phytosterol ester purity and 80% yield could be achieved. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Supercritical fluid extraction of minor lipids from pretreated sunflower oil deodorizer distillates

The recovery of minor lipid compounds (tocopherols and phytosterols) from sunflower oil deodorizer distillates using countercurrent supercritical carbon dioxide extraction has been studied. Since the raw material employed contains large amounts of triacylglycerols and free fatty acids, chemical transformation of these compounds into their corresponding fatty acid ethyl esters was previously carried out, in order to favor the concentration of minor lipids in the raffinate product. Extractions of the original and pretreated raw material were carried out in a pilot‐scale plant at 65 °C, with pressures ranging from 15 to 23 MPa and solvent‐to‐feed ratios from 15 to 30. The influence of the feed composition in the extraction process was analyzed by comparison of the tocopherol and phytosterol yields and enrichment factors obtained in each case. The chemical transformation of the deodorizer distillate composition significantly enhances the concentration of minor lipids in the raffinate product. Additionally, the reaction step produced a solid phase, mainly consisting of sterols, which was isolated from the liquid product.     

Comparison of Supercritical Fluid and Hexane Extraction Methods in Extracting Kenaf (<Emphasis Type="Italic">Hibiscus cannabinus</Emphasis>) Seed Oil Lipids

The objective of this study was to investigate and compare fatty acids, tocopherols and sterols of kenaf seed oil extracted by supercritical carbon dioxide and traditional solvent methods. Fatty acids, tocopherols and sterols were determined in the extracted oils as functions of the pressure (400 bar, 600 bar), temperature (40 °C, 80 °C) and CO₂ flow rate (25 g/min) using a 1-L extraction vessel. Gas chromatography was used to characterize fatty acids and sterols of the obtained oils while tocopherols were quantified by HPLC. No differences were found in the fatty acid compositions of the various oil extracts and the main components were found to be linoleic (38%), oleic (35%), palmitic (20%) and stearic acid (3%). Extraction of tocopherols using high pressure (600 bar/40 °C, 600 bar/80 °C) gave higher total tocopherols (88.20 and 85.57 mg/100 g oil, respectively) when compared with hexane extraction which gave yield of 62.38 mg/100 g oil. Extraction of kenaf seed oil using supercritical fluid extraction at high temperature (80 °C) gave higher amounts of sterols when compared with hexane extraction.     

Kinetics of supercritical carbon dioxide extraction of borage and evening primrose seed oil

In the present work, high‐pressure extraction of borage (Borago officinalis L.) and evening primrose (Oenothera biennis L.) seed oil, containing the valuable γ‐linolenic acid (GLA), has been investigated. Extraction was performed with supercritical carbon dioxide on a semi‐continuous flow apparatus at pressures of 200 and 300 bar, and at temperatures of 40 and 60 °C. A constant flow rate of carbon dioxide in the range from 0.17 to 0.20 kg/h was maintained during extraction. The extraction yields obtained using dense CO₂ were similar to those obtained with conventional extraction using hexane as solvent. The composition of extracted crude oil was determined by GC analysis. The best results were obtained at 300 bar and 40 °C for both seed types extracted, where the quality of oil was highest with regard to GLA content. The evening primrose seed oil extracted with supercritical fluid extraction was particularly rich in unsaturated fatty acids: up to 89.7 wt‐% of total free fatty acids in the oil. The dynamic behavior of the extraction runs was analyzed using two mathematical models for describing the constant rate period and the subsequent falling rate period. Based on the experimental data, external mass transfer coefficients, diffusion coefficients and diffusivity in solid phase were estimated. Results showed good agreement between calculated and experimental data.     

Supercritical Fluid Extraction and Chromatography of Lipids in Bilberry

A supercritical fluid extraction (SFE) method has been developed for the extraction of lipids in bilberry. Experimental design was used to optimize pressure, temperature and extraction time using CO₂ as solvent. Best SFE condition for total lipids was 450 bar, 60 °C and 45 min. The SFE method was compared to conventional Bligh & Dyer (B&D) extraction. The amount of fatty acid methyl esters (FAME) was found to be 4.84 ± 0.06 mg and 4.564 ± 0.003 mg per g of the freeze‐dried bilberry sample for the developed SFE and B&D methods, respectively, while the amount of total lipids was found to be 54.40 ± 6.06 mg and 65.70 ± 0.67 mg per g of sample for SFE and B&D, respectively. This discrepancy between FAME and total lipids could be explained by the presence of wax esters, sterol esters, carotenoids and phospholipids, as determined by supercritical fluid chromatography.     

Extraction of hiprose fruit by supercritical CO2 and propane

Extraction of whole fruit, seeds and peel of hiprose were studied with carbon dioxide, propane + carbon dioxide and propane as solvents under super- and subcritical conditions. The percentage of extract recovered from seed, whole hipfruit and hippeel was found to be 5.7–6.7, 3.0–3.5 and 0.32–0.42, respectively. The ratios of solvent to plant material, required to attain a complete extraction, were found to be 10 applying CO₂ at 35 °C and 250 bar, 3 using a solvent mixture rich in propane at 28 °C and 100 bar, and 1.1 with propane at 25 °C and 50 bar. As determined by high-performance liquid chromatographic (HPLC) methods the biologically active compounds such as carotenoids and tocopherols occur mainly in the peel of hipfruit. The oils from hip seeds increase extractability of such compounds in SF-CO₂ alone or with propane. Of the fatty acid analysed linoleic acid (C18:2) was the most abundant (52–55%) followed by linolenic acid (C18:3) which accounted for 23–24% of the total fatty acid species. No significant changes were observed in fatty acid composition of the extracts as a function of changes in the conditions of sub- and supercritical extraction.     

Supercritical fluid extraction of oil from millet bran

Proso millet bran [Panicum miliaceum (L.)], variety Dakota White, was extracted with supercritical carbon dioxide (SC-CO₂) to yield crude oil. The effects of operating parameters (pressure, temperature, and specific solvent flow) and of features of the raw material (moisture content and particle size) on oil extraction were investigated. Complete de-oiling of ground millet bran pellets was achieved under 300 bar at 40°C with a specific solvent flow of 2–10 h⁻¹ within 200 to 500 min. Solvent requirements were 20–30 kg CO₂/kg raw material. Composition of crude SC-CO₂ oil extracted under optimal conditions, i.e., fatty acid profile, amount of unsaponifiables, tocopherols, free fatty acids, sterols, sterol esters, waxes, hydrocarbons, and phospholipids, was compared to that of crude oil obtained by petroleum ether extraction. These two oils were similar in terms of fatty acid profile and amount of free fatty acids, unsaponifiables, peroxides, and tocopherols. They differed in respect to phospholipids (present in petroleum etherextracted oil and absent in SC-CO₂ extracted oil), metals, and waxes (lower levels in SC-CO₂ extracted oil). The effects of extraction procedures on oxidative stability of crude SC-CO₂ oil were studied. Ensuring that all pieces of the extractor in contact with the oil were in stainless steel; cleaning the separator, i.e., washing with KOH, rinsing, purging with N₂ and CO₂, and heating; performing a couple of extractions before the main extraction; and achieving the extraction without interruption all positively influenced the oxidative stability of the oil. Conversely, increasing CO₂ purity above 99.5% had no effect. Oxidative stability of the SC-CO₂ oil extracted under these conditions was only slightly lower than that of the oil extracted with petroleum ether.     

Comparison of a supercritical fluid extraction method for the extraction of oilseeds with the DGF standard method B-I 5 (87)

Three different oilseeds, rapeseed, sunflower, and soybeans are extracted by SFE (supercritical fluid extraction). As parameter for the extraction conditions the extracts are analyzed regarding the contents of tocopherols, and as parameter for the content of more polar lipids the contents of diglycerides and free fatty acids are analyzed. The extraction temperature has a significant influence on the determined oil content, the content of tocopherols, diglycerides, and free fatty acids. With increasing temperature the oil content increases. The content of tocopherols, diglycerides, and free fatty acids increases up to 75 °C. At 100 °C the content of diglycerides and free fatty acids decreases and the content of tocopherols shows no appreciable changes. The optimal extraction conditions are described and the results of the determination of the oil content under optimal conditions are compared with the results of the DGF standard method B-I 5 (87). The oil contents investigated with both methods correspond well. The content of tocopherols is significantly higher in the oil of rapeseed and soybeans extracted by SFE, whereas the content of diglycerides and free fatty acids varied in dependence on the oilseed.     

Use of the Product from Low Pressure Extraction (Crambe Seed Oil and Methyl Acetate) for Synthesis of Methyl Esters and Triacetin Under Supercritical Conditions

Methyl esters (ME) and triacetin production from the supercritical interesterification of the product from low pressure extraction (crambe seed oil and methyl acetate) are evaluated. Reactions are conducted at 300–375 °C for different residence times, at 20 MPa, and under these conditions the thermal stability of triacetin is evaluated. The effect of the free fatty acid (FFA) concentration (in oil) is determined. An increase in temperature favors the formation of ME and triacetin at shorter reaction times. At 375 °C, after 15 min a drop in the ME yield is observed and triacetin is not detected. A reduction in the triacetin concentration (reaching ≈99%) is observed at 375 °C. High FFA concentration (in oil) initially provided higher product generation, however, after 15 min no influence is observed. The highest ME yield (≈60%) is obtained at 300 °C, along with 1.22 wt% triacetin and ≈5.0 wt% unreacted compounds. Practical Applications: This paper reports new experimental data on an integrated process for the production of methyl esters from low pressure extraction (crambe seeds and methyl acetate) and supercritical reaction of the extraction mixture. The technique used allows the removal of a high quantity of oil from good quality crambe seeds. The viability of applying the integrated process to obtain oils with a high content of free fatty acids is verified, promoting the obtainment of relatively simple methyl esters. The procedure does not require oil purification and solvent recovery prior to the reaction.     

Comparison of supercritical CO2 and hexane extraction of lipids from sorghum distillers grains

Total yields and compositions of sorghum dried distillers grains with solubles (DDGS) lipids obtained by supercritical CO₂ (SC‐CO₂) extraction were compared with those obtained by recirculated solvent extraction (RSE) with hexane. The total yield of lipids obtained by SC‐CO₂ extraction at 27.5 MPa and 70 °C was 150 g lipids/kg DDGS, while the yield obtained by RSE with hexane at 69 °C was only 85 g lipids/kg DDGS. The contents of four high‐value compounds, i.e., policosanols, phytosterols, free fatty acids (FFA) and tocols, in the lipids obtained by SC‐CO₂ extraction were 31.2, 15.6, 155.3 and 0.50 mg/g at 27.5 MPa and 70 °C, compared to 26.6, 9.6, 57.3 and 0.03 mg/g for RSE with hexane at 69 °C. The profiles of phytosterols and FFA in the sorghum DDGS lipids were relatively independent of the extraction methods and operating conditions.     

Phase behavior of semicrystalline polyester resin in supercritical fluid solvents and solvent mixtures: Implications for supercritical fluid processing

Cloud‐point data between 40 and 240°C and pressures to 2750 bar are presented for a low molecular weight, semicrystalline polyester resin of 53.4 mol % adipic acid and 46.6 mol % 1,4‐cyclohexanedimethanol in supercritical CO₂, dimethyl ether (DME), and chlorodifluoromethane (CDFM), and in mixtures of CO₂ with DME, CDFM, methanol, ethanol, butanol, octanol, hexafluoroisopropanol, acetone, and cyclohexane. Carbon dioxide, by itself, is an extremely weak supercritical fluid (SCF) solvent because this polyester only dissolves at pressures in excess of 2000 bar and at temperatures over 180°C. However, DME and CDFM are excellent solvents for this polyester, which dissolves at 16 bar and 40°C in CDFM and at 167 bar and 55°C in DME. The melting point of this polyester is reduced from 105 to 40°C in CDFM and to 55°C in DME, which makes the polyester amenable to high intensity mixing for the efficient dispersion of inorganics or crosslinking agents and other hard to deposit materials. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2642–2648, 2001     

Antioxidant effect of mono‐ and dihydroxyphenols in sunflower oil with different levels of naturally present tocopherols

Antioxidant properties of mono‐ and dihydroxyphenolic acids and their alkyl esters were examined, with emphasis on the relationship between their molecular structure and antioxidant activity. Test media with different tocopherol level were used for determining the oxidative stability: original refined sunflower oil (total tocopherols 149.0 mg/kg), partially tocopherol‐stripped sunflower oil (total tocopherols 8.7 mg/kg) and distilled fatty acid methyl esters (FAME) as a tocopherol‐free medium. The chemical reaction of tocopherols with diazomethane tested for the purpose to eliminate their antioxidant activity failed due to the negligible degree of methylation of hydroxyl group in the tocopherol molecule. Caffeic acid and protocatechuic acid (3,4‐dihydroxyphenolic acids) and their alkyl esters were found to be more active antioxidants than monohydroxyphenolic acid (p‐hydroxybenzoic acid), 2,5‐dihydroxyphenolic acid (gentisic acid), 3‐methoxy‐4‐hydroxyphenolic acids (vanillic and ferulic acids) and their corresponding alkyl esters. Naturally present tocopherols in refined sunflower oil proved to have a synergistic effect on gentisic acid but not on its alkyl esters. In contrast, tocopherols showed an antagonistic effect on alkyl esters of caffeic acid, because their protection factors decreased with increasing level of tocopherols in the test medium. Moreover, the antioxidant activity of these alkyl esters decreased with increasing length of their alkyl chain in conformity with the polar paradox hypothesis. Practical applications: Tocopherols as naturally present antioxidants influence considerably the antioxidant activity of other antioxidants added to plant oils used as a test medium. Distilled fatty acid methyl esters prepared from refined sunflower oil may serve as an optimal tocopherol‐free test medium. Some alkyl esters of phenolic acids were evaluated to be applicable as natural more lipophilic antioxidants in comparison with phenolic acids.     

Effect of Tocopherols on the Anti-Polymerization Activity of Oryzanol and Corn Steryl Ferulates in Soybean Oil

Steryl ferulates (SFs) are ferulic acid esters of phytosterols and/or triterpene alcohols which have potential as frying oil antioxidants. The objective of this study was to evaluate the anti-polymerization and antioxidant activity at frying temperatures of corn steryl ferulates (CSFs), rice steryl ferulates (oryzanol), and a mixture of CSFs with oryzanol, alone and with tocopherols. Antioxidant activity was measured by the reduction of polymerized triacylglycerol formation, and loss of olefinic and bisallylic protons from fatty acid double bonds by ¹H NMR. CSFs and oryzanol slowed the oxidation and polymerization of soybean oil triacylglycerols heated to 180 °C more effectively than a mixture of alpha and gamma tocopherols. CSFs were more effective at preventing polymerization than oryzanol, but when oryzanol was combined with tocopherols, they all had similar antioxidant activity. In addition, tocopherols had a protective effect on SFs. Corn SFs were degraded more quickly during heating than oryzanol, however, the phytosterol constituents of corn SFs, sitostanol and campestanol, were actually more resistant to degradation compared to the phytosterol constituents of rice SFs. Results demonstrate that corn and rice SFs may be effective antioxidants for use in frying oils, and that their activity is enhanced in the presence of tocopherols.     

Concentration of tocopherols from soybean sludge by supercritical carbon dioxide

A supercritical fluid extraction method has been applied to test the feasibility of tocopherol concentration from soybean sludge with carbon dioxide at temperatures and pressures ranging from 35 to 70°C and 200 to 400 bar, respectively. The supercritical solubility of the esterified soybean sludge was over 4–6 times greater than that of the original soybean sludge. By a simple batch-type one-stage method the tocopherols in the esterified soybean sludge could be concentrated up to 40 wt%. The overall results of the present study show that soybean sludge initially containing about 13–14 wt% tocopherols may require a countercurrent multistage column to be highly and effectively concentrated.     

Quality of wheat germ oil extracted by liquid and supercritical carbon dioxide

The extraction of wheat germ oil by liquid and supercritical CO₂ is described from the point of view of both operative method and pretreatment of raw material. The best conditions for wheat germ oil extraction are: pressure, 150 bar; temperature, 40°C; and solvent flow rate, 1.5 L/min at standard temperature and pressure. The yields and fatty acid compositions obtained are very similar to those resulting from the conventional extraction process using hexane as solvent (8.0 wt%), although a higher-quality oil is obtained by using CO₂ as solvent (free fatty acids, 12.4%; tocopherol content, 416.7 mg tocopherol/g wheat germ oil). These factors lead to the conclusion that the extraction process using CO₂ could be economically competitive with the conventional process, since it considerably simplifies the oil refinement stages and completely eliminates the solvent distillation stage, which are the most costly processing steps in terms of energy consumption.     

Esterification affects phytosterol oxidation

The effect of esterification with rapeseed oil fatty acids on the oxidation reactions of sitosterol, campesterol and sitostanol was investigated, as well as the interactions between phytosterol/stanol compounds and the saturated lipid matrix at 100 °C and 180 °C. Free and esterified phytosterols differed in their reactivity in terms of the formation and profile of secondary oxidation products. Phytosteryl esters were more reactive than free phytosterols during prolonged heating at 100 °C. In contrast, free phytosterols were slightly more reactive than phytosteryl esters at 180 °C. The oxidation reactions of phytostanol compounds were low under all conditions studied. Changes in the phytosterol compounds during heating were also studied via the losses in the original phytosterol contents. This study revealed that the formation of secondary oxides did not account for all the phytosterol losses; this indicates the presence of other oxidation products, especially at 180 °C, and during the heating of free sitosterol. Thus, in order to understand the overall deterioration of phytosterol and phytostanol compounds, both the secondary oxide formation and the sterol loss need to be studied. The deterioration of the saturated lipid matrix used in this study was rather low and was mainly associated with the heating temperature and time.     

Isolation of tocopherol and sterol concentrate from sunflower oil deodorizer distillate

The isolation of tocopherols and sterols together as a concentrate from sunflower oil deodorizer distillate was investigated. The sunflower oil deodorizer distillate was composed of 24.9% unsaponifiable matter with 4.8% tocopherols and 9.7% sterols, 28.8% free fatty acid (FFA) and 46.3% neutral glycerides. The isolation technology included process steps such as biohydrolysis, bioesterification and fractional distillation. The neutral glycerides of the deodorizer distillates were hydrolyzed byCandida cylindracea lipase. The total fatty acids (initial FFA plus FFA from neutral glycerides) were converted into butyl esters withMucor miehei lipase. The esterified product was then fractionally distilled in a Claisen-vigreux flask. The first fraction, which was collected at 180–230°C at 1.00 mm of Hg for 45 min, contained mainly butyl esters, hydrocarbons, oxidized products and some amount of free fatty acids. The fraction collected at 230–260°C at 1.00 mm Hg for 15 min was rich in tocopherols (about 30%) and sterols (about 36%). The overall recovery of tocopherols and sterols after hydrolysis, esterification and distillation were around 70% and 42%, respectively, of the original content in sunflower oil deodorizer distillate.     

Dealcoholisation of Cider by Supercritical Extraction with Carbon Dioxide

A study of cider dealcoholisation by supercritical extraction with carbon dioxide using pilot-plant-scale equipment has been carried out. The effects of pressure, temperature and solvent to feed ratio have been examined. Supercritical and liquid carbon dioxide have been used to extract ethanol and aromas from cider at pressures of 80–250 bar and temperatures of 20 and 40°C.     

The Fractional Extraction of Lipids and Cholesterol from Dried Egg Yolk Using Supercritical Carbon Dioxide

Results from extraction of cholesterol and other lipid components from dried egg yolk using supercritical carbon dioxide at the range of temperature from 40°C to 60°C and pressure between 150 bar und 350 bar for 2.5 hours and 2.7 kg CO₂ consumption is described in this paper. The solubility of lipids and cholesterol increased with the increase of pressure at a constant temperature of 50°C, while at a constant pressure, more cholesterol was removed at 45°C than that at other temperatures. Nearly 60 percent cholesterol was removed at 45°C and 250 bar. Lipids were more efficiently extracted at 60°C than at 40°C at 250 and 350 bar, however, a decrease in the total extracted lipids was observed with the increase in temperature at 150 bar. The removed total lipids from dried egg yolk at 250 bar/55°C was over 80 %.     

In-line and off-line trapping of lipids extracted from chicken liver by supercritical carbon dioxide

This supercritical fluid extraction study determined the retentive properties of neutral alumina sorbent as an in-line trap for lipids in the dynamic state over a pressure range of 490–680 bar and temperatures of 40 and 80°C. Lipids were extracted from a chicken liver matrix using supercritical carbon dioxide over a 40-min period at a flow rate of 3 L/min (expanded gas), then were quantified by high-performance liquid chromatography using an evaporative light-scattering detector. Approximately 30 and 18%, respectively, of the total extracted lipids were trapped on the in-line alumina sorbent bed at 40°C as the operating pressure increased from 490 to 680 bar, while the remaining lipids were trapped off-line after CO₂ decompression. The major lipid classes trapped in-line were fatty acids and cholesterol, whereas only minor amounts of the less polar lipid classes such as sterol esters and triacylglycerols were retained. At 80°C and 680 bar, less than 1.5% of the extracted total lipids was trapped in-line, indicating the lack of adsorptive selectivity for lipids by alumina under these conditions.