Extraction of Linum usitatissimum L. Using Supercritical CO 2 and Organic Solvent

Transcription

1 Extraction of Linum usitatissimum L. Using Supercritical CO 2 and Organic Solvent E. L. Galvão 1, H. N. M.Oliveira, 1 A. V. B. Moreira, 2 and E. M. B. D. Sousa 1* 1 Departamento de Engenharia Química, Universidade Federal do Rio Grande do Norte, Campus Universitário s/n, CT/DEQ/PPGEQ, Lagoa Nova , Natal-RN, Brazil. 2 Departamento de Nutrição, Universidade Federal do Rio Grande do Norte, Av. Gen. Cordeiro de Farias, s/n. Petrópolis Natal- RN, Brasil. *Corresponding author address: elisa@eq.ufrn.br Fax: ABSTRACT In this study, experimental results of brown linseed extraction are presented. Comparative analysis was performed between supercritical CO 2 extraction (SC-CO 2 ) and organic solvent extraction (OS). The experiments were conducted in a SFE unit containing a fixed bed cell. Oil extraction was carried out at 30 MPa and K. OS extraction consists of: sample incubation, vacuum filtration and solvent evaporation. Extraction yields using OS were higher than those obtained with the SC-CO 2 technique. Characterization of the extracts was performed using the GC system. The results showed the presence of linoleic and linolenic acids as the main components in both techniques. INTRODUCTION The extraction of essential oils and vegetables using supercritical fluids as solvent is a technique that has been gaining worldwide prominence. The success of the technique is due to the characteristics that the fluids exhibit under supercritical conditions, that is, physical-chemical properties between those of a liquid and a gas, which increases their solvent action. Their relatively high density also contributes to their high-solvency power, while their high diffusivity values along with low viscosity give them a considerable power of penetration into the solute matrix [1]. The most widely used solvent has been carbon dioxide (isolated or with the addition of co-solvents), because of its favourable properties, such as ease of separation, non-toxicity, non-flammability, inertness, etc. The advantage of using this technique over conventional extraction methods is the purity of the product at the end of the process, given the absence of residues. Another advantage is that this technique is considered clean and environmentally correct, since CO 2 can be recovered at the end of the process. The literature is replete with studies that used this technique to obtain vegetables and essential oils [2]. Linseed is highly oleaginous (around 40%) and rich in alpha-linolenic acid [3]. It is widely used in the production of paint, resin and varnish [4]. In this study, experimental results of brown linseed oil extraction are presented. A comparative analysis was performed between

2 supercritical extraction (SC-CO 2 ) and extraction with organic solvents (OS) in order to observe the influence of extraction technique on the process yield and the composition of the final product, mainly in terms of linoleic and alpha-linolenic acid content. MATERIALS AND METHODS Two extraction techniques were used to obtain the linseed oil: i) extraction with supercritical CO 2 (SC-CO 2 ) at 300 bar and 70ºC, with and without the addition of 5% (v/v) ethanol as co-solvent; ii) extraction with organic solvent (OS), where two solvents were tested, ethanol and ethyl ether. The experiments were carried out to determine which of the techniques used would result in the highest recovery of linoleic and alpha-linolenic acids. Raw Material Preparation The samples of brown linseed (Linum usitatissimum L.) used in the experiments were obtained from 3 supermarkets in Natal (Brazil), homogenized, stored in vials and maintained below -20ºC until use. The seeds were ground in a domestic multiprocessor (ARNO, model PRO, Brazil) for 10 s. Moisture content was determined by the AOCS 2-54 method [5]. To obtain the extracts using the OS technique, the ground seeds were separated on a 24mesh Tyler sieve. For the SC-CO 2 technique, samples of 138 ± 2g (capacity of the extractor column) were prepared at predetermined granulometry (30% of 24 mesh, 30% of 28 mesh, 20% of 32 mesh and 20% of 48 mesh). The experiments were performed in duplicate for each experimental condition tested. SC-CO 2 Extraction For this extraction technique, the linseed sample is placed in an extractor column, forming a fixed bed of particles through which the supercritical CO 2 drains. Thus, the desired components (linseed oil) are transported from the solid phase (seed) to the supercritical fluid phase. A experimental extraction unit built in the Laboratory of Supercritical Technology of UFRN (Brazil) it was used in the experiments. The extraction conditions were: Condition 1: P = 300 bar, T = 70ºC, mean flow rate of 1.5gCO 2 /min, without the addition of co-solvent. Condition 2: P = 300 bar, T = 70ºC, mean flow rate of 1.5gCO 2 /min, with the addition of ethanol as co-solvent at 5% (v/v). Extraction time was fixed at 4h for each experiment. Organic Solvent Extraction (OS). The methodology used for extraction by organic solvents was developed by Povh [6]. It consists of three stages: sample incubation, vacuum filtration and solvent evaporation. The samples (30 g of brown linseed at a granulometry of 24 mesh ml of solvent ethanol or ethyl ether) were incubated at 15ºC and agitated at 190 rpm for 8h. This was followed by vacuum filtration, where the extracts were separated from the solid matrix, weighed and placed in Petri

3 plates to evaporate the solvent at a temperature of 20ºC. After the solvent was completely evaporated, the plates were weighed and extraction yield was calculated from the ratio between the total mass of the extract present in the filtrate and the initial mass of linseed used. The product of each extraction was conditioned and stored below -20ºC for subsequent analyses. Extract Analysis The extracts produced by both techniques (OS, SC-CO 2 ) were sterified and the samples were prepared to obtain fatty acid methyl esters (FAME) and subsequent chromatographic analyses. Obtaining Fatty Acid Methyl Esters. Hartman and Lago s [7] method was used to prepare the fatty acid methyl esters. The methyl esters obtained were resuspended in 1 ml of hexane. This solution was injected into the chromatograph. Gas Chromatography. The analyses were performed by capillary gas chromatography CGC AGILENT 6850 SERIES GC SYSTEM. An AGILENT DB-23 capillary column (50% cyanopropylmethylpolysiloxane, 60m x 0.25 mm x 0.25 µm) was used. The chromatographic conditions were the following: 1) Temperature gradient: initial temperature was 110 C for 5 min, and heat was increased by 5 C/min up to 215 C, remaining at this temperature for 24 minutes; 2) Vaporizer temperature: 250 C; 3) Detector temperature: 280 C; 4) Carrier gas: He (1.0 μl) with flow rate of 1mL/min. The identification of fatty acids in the samples was compared to the spectra of fatty acid patterns determined under the same conditions. RESULTS Process yield The yield of each extraction process used to obtain linseed oil is shown in Table 1. The yield values were calculated from the ratio between the mass of oil obtained and the mass of the sample used. Table 1. Linseed oil extraction: yield x extraction technique. Code a Extraction technique Solvent Yield (%) LOSET Ethanol 6.1 ± 1. 8 OS b LOSER Ethyl ether 25.9 ± 1.3 LSC CO ± 0.7 LSCE c SC-CO 2 CO 2 + co-solvent (ethanol at 5% v/v) 15.4 ± 2.6 (a) See nomenclature. (b) Organic solvent extraction. (c) Supercritical CO 2 extraction

4 According to Table 1, the highest yield values were obtained for extraction with ethyl ether organic solvent (SO), with percentages of 25.9 %. The same technique, using ethanol as solvent resulted in much lower yields of around 6.1 %. These results were expected, since ethyl ether is an extraction solvent with wider applications than those of ethanol. In addition to oil, it is capable of extracting phospholipids, pigments and unsaponifiable substances, resulting in higher yield values [8]. Supercritical extraction with CO 2 (SC-CO 2 ) had a mean yield of 10.3% for the extractions performed without the addition of co-solvent and mean yield of 15.4% when 5% (v/v) ethanol was used as co-solvent. An increase of around 50% was obtained with the addition of ethanol as co-solvent. This result may be attributed to the fact that CO 2 is an apolar substance, which would compromise the solubilization of some of the oil components. In these cases, the use of polar cosolvents is indicated to increase recovery of the most polar components. FA Composition The main fatty acids found in the brown linseed extracts were palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2) and α-linolenic (C18:3). The mean FA concentration values as a function of the extraction technique used are shown in Table 2. The table shows that the percentage of the main fatty acids found in linseed oil did not change significantly with the extraction technique. The saturated (palmitic and stearic) and monosaturated (oleic) fatty acids were found in higher concentrations for the LOSET (linseed extraction by the OS technique with ethanol as solvent) experimental condition, with percentages of 8.4% for palmitic acid, 6.8% for stearic and 23.7% for oleic. As for α-linolenic acid content, the LOSET sample suffered a statistically significant loss (p < 0.05) when compared to the other samples, which had mean C18:3 preservation of around 51.5%. No statistically significant differences were found for the remaining fatty acids. Table 2. Fatty acid composition (% m/m) of linseed oil obtained by different extraction techniques. Fatty acid LOSET a LOSER a LSC a LSCE a Palmitic (C16:0) Stearic (C18:0) Oleic (C18:1) Linoleic (C18:2n-6) Linolenic (C18:3n-3) ni b (a) See nomenclature. (b) Unidentified Figure 1 shows the profile of linoleic fatty (C18:2n-6) and α-linolenic acids (C18:3n-3) in brown linseed oil for all the experimental conditions tested.

5 Percentile (%) C18:3n-3 C18:2n LOSET LOSER LSC LSCE Experiments code Figure 1. Profile of linoleic and α-linolenic fatty acids in the different extraction techniques. The higher recovery of α-linolenic acid (53.2%) was obtained by the OS extraction, with ethyl ether as solvent. For linoleic acid, the highest percentage (15.2%) was also obtained with the use of organic solvents. There was no significant difference between the solvent type used (ethanol or ethyl ether). Considering only the supercritical technique (SC-CO 2 ), the highest percentage of α-linolenic acid (51.4%) was obtained for trials that used 5% (v/v) ethanol as cosolvent (LSCE). CONCLUSION The different extraction techniques tested (OS and SC-CO 2 ) for obtaining brown linseed oil resulted in satisfactory yields, the highest value (25.9%) reached with the OS technique and ethyl ether as solvent (LOSER trial). This experimental condition also yielded the highest α- linolenic fatty acid recovery (53.2%). As to the percentage of the remaining fatty acids for the experimental conditions tested, no significant differences were found with the use of different extraction techniques. ACKNOWLEDGMENTS We wish to express our gratitude to the collaborators of the Oils and Fats Laboratory- FEA/UNICAMP (Brazil) and to the National Council for Scientific and Technological Development (CNPQ) for financial support.

6 NOMENCLATURE LOSET- linseed extracted by the OS technique with ethanol as solvent. LOSER- linseed extracted by the OS technique with ethyl ether as solvent. LSC-linseed extracted by the SC-CO2 technique without co-solvent. LSCE- linseed extracted by the SC- CO2 technique with ethanol as co-solvent. REFERENCES 1. BRUNNER, G. Gas Extraction: An introduction to fundamentals of supercritical fluids and the application to separation processes, Springer, New York, GALVÃO, E.L. Extração do óleo essencial de Cymbopogon winterianus J. com CO 2 pressurizado, Ph.D. Thesis, UFRN, Natal, Brasil, 2004, p RATNAYAKE, W. M. N.; BEHRENS, W. A.; FISHER, P. W. F.; L ABBÉ, M. R.; MONGEAU, R.; BEARE-ROGERS, J. L., J. Nutr. Biochem, Vol 3, 1992, p BICKERT, C.; LÜHS, W.; FRIEDT, W. Vol 2, 1994, p Official Methods and Recommended Practices of the American Oil Chemistis Society, 4 th edn., AOCS Press, Champaign, Vol 1, POVH, N. P. Obtenção do óleo essencial de camomila (Matricaria recutita L. Rauschert) por diferentes métodos: destilação por arraste a vapor, extração com solventes orgânicos e extração com CO 2 supercrítico, Ph.D. Thesis, FEA, Universidade Estadual de Campinas, Campinas, Brasil, 2000; p HARTMAN, L.; LAGO, R.C.A., Lab. Pract., Vol. 22, 1973, p CECCHI, H. M. Fundamentos teóricos e práticos em análise de alimentos. Campinas, SP Editora da Unicamp, p.