Argan oil has been extracted using supercritical CO2. The influence of the variables pressure (100, 200, 300, and 400 bar) and temperature (35, 45, 55°C) was investigated. The best extraction yields were achieved at a temperature of 45°C and a pressure of 400 bar. The argan oil extracts were characterized in terms of acid, peroxide and iodine values, total tocopherol, carotene, and fatty acids content. Significant compositional differences were not observed between the oil samples obtained using different pressures and temperatures. The antioxidant capacity of the argan oil samples was high in comparison to those of walnut, almond, hazelnut, and peanut oils and comparable to that of pistachio oil. The physicochemical parameters of the extracted oils obtained by SFE, Soxhlet, and traditional methods are comparable. The technique used for oil processing does not therefore markedly alter the quality of argan oil.
Generally, this oil is rich in unsaturated fatty acids (80%), principally oleic, and linoleic acids (44.8 and 33.7%, resp.). Interestingly, the unsaponifiable fraction (1% of the oil constituents) of argan oil is mainly rich in antioxidant compounds such as tocopherols, which is present in a higher proportion compared to olive oil (637 mg/kg versus 258 mg/kg, resp.) and especially in its
Chemical composition of argan oil and olive oil [
Argan oil | Olive oil | |
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Tocopherols (mg/kg oil) | ||
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480 ± 7 | 26 ± 1 |
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35 ± 1 | 190 ± 1 |
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122 ± 10 | 42 ± 2 |
Total |
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Sterols (mg/100 g oil) | ||
Schottenol | 142 ± 11 | nd |
Spinasterol | 115 ± 7 | nd |
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9 ± 1 | nd |
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nd | 156 ± 3 |
Campesterol | nd | 12 ± 1 |
Stigmasterol | nd | nd |
Others | 29 ± 1 | 151 ± 10 |
Phenolic compounds ( |
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Vanillic acid | 67 ± 3 | 359 ± 7 |
Syringic acid | 37 ± 5 | 0 |
Ferulic acid | 3147 ± 20 | 51 ± 2 |
Tyrosol | 12 ± 1 | 19,573 ± 37 |
Others | 0 | 773,000 ± 53 |
Total |
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Squalene (mg/100 g oil) | 314 ± 1 | 499 |
nd: not detected.
By far the main traditional use of argan oil is for nutritional purposes. Natives either eat the oil directly on toasted bread, generally for breakfast, or use it for cooking.
As a cosmetic product, the oil is traditionally used to cure all kinds of skin pimples and, more particularly, juvenile acne and chicken pox pustules [
In addition, and in a similar way to olive oil, argan oil is also administered orally, and it is traditionally prescribed as a choleretic, hepatoprotective agent and in cases of hypercholesterolemia and atherosclerosis.
The method employed to extract the oil from nuts is complex and has a considerable influence on the physicochemical composition, nutritional value, and sensorial properties of the oil [
For many years, argan oil has been prepared exclusively by Berber women according to an ancestral multistep process [
Traditional oil extraction is frequently carried out in unsatisfactory sanitary conditions. As a result, several cooperatives aim to produce and commercialize quality-certified virgin argan oil using a semi-industrial method with mechanical cold-pressing without the addition of water [
For industrial or laboratory purposes, argan oil can be extracted from ground kernels using any volatile lipophilic solvent. The solvent is evaporated to give the oil in 50–55% yield. However, this type of extraction furnishes oil with unsatisfactory organoleptic properties compared to the traditional or press-extracted oil. As a consequence, this technique is exclusively used to prepare argan oil for cosmetic purposes [
Another product that is also used exclusively for cosmetic purposes is the so-called “enriched argan oil”, which can be prepared by flash distillation, under reduced pressure at 270°C, of the crude oil previously obtained by pressextraction. The level of unsaponifiable matter contained in this oil is three times higher than the value observed for the press-extracted oil.
Supercritical fluid extraction (SFE) is considered to be an environmentally benign alternative to the conventional extraction of triglycerides. SFE has been successfully used to obtain oil from seeds of apricot [
In this paper we present a study into the extraction of argan oil using supercritical CO2 for cosmetics uses. CO2 is the most widely used supercritical fluid because it is nontoxic, nonflammable and is available at low cost and with a high degree of purity. Furthermore, the use of CO2 is acceptable in the food and pharmaceutical industries. Despite the numerous studies on this kind of supercritical extraction, literature the concerning the extraction of argan seeds is lacking in terms of SFE. The quality of the oil obtained is also compared with other examples reported in the literature.
Argan seeds were used in this study. The fruit was collected in May 2011 in Morocco. The fruit was sun-dried for seven days to constant weight, and the dried peel was manually removed to provide the argan nuts. The argan seeds were ground to obtain the appropriate particle size distribution (mean size 0.8 mm).
Carbon dioxide (99.995%) was supplied by Abello-Linde S.A. (Barcelona, Spain). 2,2-Diphenyl-1-picrylhydrazyl free radical (DPPH), methyl ester standards of fatty acids,
The oil extractions at high pressure were carried out in equipment supplied by Thar Technology (Pittsburgh, PA, USA, model SF100) provided with an extraction vessel (capacity of 100 mL) and a pump with a maximum flow rate of 50 g/min of carbon dioxide. The extraction temperature was controlled with a thermostated jacket. The cyclonic separator allowed periodic discharge of the extracted material during the SFE process. The extraction system is represented in Figure
Schematic diagram of the equipment.
The operating methodology involved loading the extraction vessel with approximately 15 g of the sample, which had previously been homogenized in order to maintain a constant apparent density in all experiments of 520 Kg/m3. Since the apparent density of all samples was approximately constant, porosities were also constant and equal to
The extracts were collected in a cyclonic separator and transferred to glass bottles, which were stored at 4°C with the exclusion of light.
The experiments on each sample were carried out in duplicate in order to evaluate the variability of the measurements. Experiments were carried out at different temperatures and pressures. The measured flow rate for the supercritical fluids was 20 g/min for 3 hours.
The oil extraction was also carried out using a Soxhlet extraction system with hexane as solvent. An extraction time of 8 hours was chosen. After extraction, the extracts were evaporated on a rotary evaporater (Laborota 4001, Germany) at 40°C, and the samples were stored at 4°C with the exclusion of light.
Refractive index and density were carried out according to the reported AOCS methods [
The acid value of each oil obtained under different conditions was analyzed according to UNE-55011. Acidity index is the mass, in mg, of potassium hydroxide that is necessary to neutralize free fatty acid present in 1 g of sample. It is usual to represent this value as percentage of oleic acid, which is the most abundant of the fatty acids [
Peroxide value is related to hydroperoxides in terms of milliequivalents per kg of oil. These hydroperoxides oxidize potassium iodide under standard conditions [
One of the most useful parameters for the characterization of oils and fats is the iodine number or value, which is a measure of unsaturation. The iodine value is defined as grams of I2 added across the multiple bonds of a 100 g sample.
The iodine value is determined using classical titration methods [
The term “unsaponifiable matter” is applied to the substances nonvolatile at 100–105°C obtained by extraction with an organic solvent from the substance to be examined after it has been saponified. Unsaponifiable matters were carried out according to the reported AOCS methods [
Fatty acid compositions were determined by gas chromatography (GC) on an Agilent Technologies model 6890N chromatograph with a TR-CN100 capillary column (60 m length × 0.25 mm internal diameter × 0.20
A preparation step was required prior to the introduction of the oil into the GC for the individual determination of fatty acid composition. The extracts obtained were treated to convert them into the corresponding fatty acid methyl ester (FAME) [
High-performance liquid chromatography (HPLC) analysis of the total tocopherol present in the extracts was performed using an Agilent Technologies 1100 Series chromatograph. The elution solvent was methanol at a flow rate of 1.0 mL/min and the column used was C18 Hypersil ODS (250 × 4.6 mm) (5
The experiments for each extraction were carried out in triplicate in order to evaluate the variability of the measurements. The results are shown as the average of all the independent analyses with a reproducibility of approximately 8% CV (coefficient of variation).
The experiments for each extraction were carried out in triplicate, and the results are shown as the average of all the independent analyses with a reproducibility of approximately 6% CV (coefficient of variation).
The antioxidant activities were determined using DPPH as a free radical. Different concentrations were tested (expressed as mg of extract/mg DPPH) for each set of extraction conditions. Extract solution in ethyl acetate (0.1 mL) was added to a 6 × 10−5 mol/L DPPH solution (3.9 mL). The decrease in absorbance was determined at 515 nm at different times until the reaction had “reached a plateau”. The initial DPPH concentration (
For each set of extraction conditions a plot of % remaining DPPH versus time (min) was generated. These graphs were used to determine the percentage of DPPH remaining at the steady state and the values were transferred to another graph showing the percentage of residual DPPH at the steady state as a function of the weight ratio of antioxidant to DPPH. Antiradical activity was defined as the amount of antioxidant required to decrease the initial DPPH concentration by 50% [Efficient Concentration = EC50 (mg oil/mg DPPH)] [
The experiments were carried out in triplicate in order to evaluate the variability of the measurements.
The extraction yields expressed as g of extracted oil/g of seeds are represented in Figure
Extraction yield of argan oil at different pressures and temperatures.
The extraction yields obtained by SFE at 45°C and 400 bar were higher (48%) than that obtained in the semi-industrial method with mechanical cold-pressing without water (45%) and far higher than those obtained by traditional methods. Unfortunately, the traditional method is very slow (for a single person 58 hours of work is necessary to obtain 2–2.5 L of oil).
The extraction yield in liquid hexane (Soxhlet) was 52% (w/w). In comparison, the yield in the supercritical fluid extraction was 48% for the experiment conducted at 45°C and 400 bar. Assuming that the oil extraction using hexane is complete, the value obtained by SFE represents 92% of the maximum value. It is important to bear in mind, however, that the extract obtained with the organic solvent has unsatisfactory organoleptic properties [
The extraction yields obtained at different temperatures and pressure were statistically analyzed. Regression analysis was performed on the experimental data and the coefficients of the model were evaluated for significance. The Pareto diagram for the analysis of the experimental design is shown in Figure
Pareto diagram and estimated extraction yields using empirical correlation (temperature °C, pressure bar).
The relationship between temperature and pressure for the extraction yield of argan oil is represented by (
In order to achieve complete extraction of the substances in question, a relatively long extraction time was used (3 h) and the low flow rate for the supercritical fluids was 1,2 kg/h. Therefore, the amount of CO2 consumed in each test was of 3.6 kg of CO2.
Some physical properties of argan oil obtained by SFE (400 bar and 45°C) and Soxhlet extraction are shown in Table
Physical properties of argan oil obtained by SFE and Soxhlet extraction. Also appear the properties of commercial oil.
SFE | Soxhlet | Commercial oil | |
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Refractive index | 1.4731 | 1.4719 | 1.4730 |
Density g cm−3 | 0.9170 | 0.9158 | 0.9166 |
Some chemical parameters of freshly prepared argan oil samples obtained with different extraction conditions are shown in Table
Chemical characteristics of argan oil obtained by SFE (pressure/temperature) and Soxhlet extraction.
100/35 | 200/35 | 200/45 | 200/55 | 300/35 | 300/45 | 300/55 | 400/35 | 400/45 | 400/55 | Soxhlet | |
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Acid value (mg/g) (±0.1) | 0.4 | 0.3 | 0.4 | 0.3 | 0.4 | 0.5 | 0.3 | 0.5 | 0.4 | 0.3 | 0.4 |
Peroxide value (Meq/Kg) (±0.1) | 0.7 | 0.5 | 0.8 | 0.8 | 0.8 | 0.7 | 0.9 | 0.5 | 0.8 | 0.9 | 1.0 |
Iodine value (g I2/100 g oil) (±0.8) | 97.7 | 93.1 | 98.5 | 95.1 | 95.7 | 97.3 | 92.9 | 96.6 | 92.1 | 95.0 | 93.4 |
Unsaponifiable matters (%) (±0.3) | 0.93 | 0.98 | 1.02 | 1.10 | 1.10 | 1.20 | 1.19 | 1.20 | 1.23 | 1.21 | 0.48 |
Acid value is a measure of free fatty acids and is usually considered to be one of the main parameters that reflect the quality of oil and degree of refining, as well as the changes in quality during storage. The presence of free fatty acid in the oil is not desirable and it can also give rise to undesired saponification reactions. It can be seen from the results in Table
Peroxide value is another important factor to characterize the quality of oils and it appears to be an indicator of the lipid oxidation and deterioration of oil properties. The oxidative stability of argan oil has been attributed to its high content in tocopherols and carotenes [
Another one of the most useful parameters for the characterization of oils is the iodine value, which is a measure of unsaturation. In this case the results obtained for the oil extracted by the Soxhlet technique are lower than those obtained by SFE.
Unsaponifiable matters were found to be lower than 1.23% (unsaponifiable matter of virgin olive oil has to be lower than 1.5 [
The four parameters described above have similar values to those reported by other authors [
The total fatty acids compositions of the extracts obtained in this study were determined by GC. Significant variations were not observed between the samples extracted at different pressures and temperatures, with oleic and linoleic acids consistently making up 80% of the fatty acids fraction. The results shown in Table
Fatty acid compositions of extracts obtained.
Fatty acid | Fatty acid composition GC area (%) | ||
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SFE CO2 | Soxhlet | Traditionally extracted oila | |
Myristic (C14:0) | 0.3–0.4 | 0.3–0.4 |
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Palmitic (C16:0) | 10.4–14.3 | 11.3–12.6 |
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Stearic (C18:0) | 4.5–6.7 | 6.7–8.7 |
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Oleic (C18:1) | 45.4–49.0 | 45.2–46.5 |
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Linoleic (C18:2) | 29.2–34.8 | 32.4–33.2 |
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Linolenic (C18:3) | 1.6–1.7 | 0.6–0.7 | Not detected |
Chromatograms obtained from (a) Commercial oil, (b) FSC oil extracted to 45°C and 400 bar.
Significant differences were not observed in the compositions of the oils obtained in this study using supercritical CO2 and the oil obtained by Soxhlet extraction with hexane. The oils contain mainly oleic acid (45.4–49.0%), linoleic acid (29.2–34.8%), and palmitic (10.4–14.3%) acids.
For the sake of comparison, the results obtained using traditional extraction methods are also shown in Table
The contents of total tocopherols and
Total tocopherol and
100 bar | 200 bar | 300 bar | 400 bar | Soxhlet | |
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Total tocopherol content in mg/kg | |||||
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35°C | 691.9 | 639.7 | 608.5 | 671.9 | 642.3 |
45°C | 689.2 | 615.2 | 586.9 | 598.3 | |
55°C | 645.3 | 698.8 | 611.1 | 603.8 | |
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35°C | 20.3 | 20.1 | 17.8 | 20.3 | 16.4 |
45°C | 20.1 | 20.1 | 18.2 | 17.1 | |
55°C | 20.8 | 21.5 | 18.5 | 18.7 |
The antiradical activities of the oils obtained at different pressures and temperatures were assessed using the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging assay. The DPPH assay is a quick, reliable, and reproducible method to assess the antiradical activities of oil. This method depends on the reduction of the purple DPPH to give a yellow-coloured diphenyl picrylhydrazine and the remaining DPPH.
The antioxidant capacity data for oils obtained at different pressures and temperatures are shown in Table
Antioxidant capacity of oils measured by the DPPH method (EC50 values, mg/mg DPPH).
100 bar | 200 bar | 300 bar | 400 bar | Soxhlet | Commercial oil | |
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35°C |
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45°C | — |
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55°C | — |
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Walnut oilb | Almond oilb | Hazelnut oilb | Peanut oilb | Pistachio oilb | ||
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The EC50 values for all oil samples are in the range 251–369 mg/mg DPPH. The EC50 value of the sample obtained by Soxhlet extraction (
Of all the pressures and temperatures investigated, the best result (lowest EC50) was obtained at 55°C/200 bar, although the conditions 35°C/400 bar also gave good results and the extraction yield was also 27% higher than that obtained at 55°C/200 bar. On the basis of these results the latter conditions should be selected for the SFE of argan oil.
The high antioxidant capacity can be attributed to present a high content on potent phenolic compounds, mainly ferulic acid known by their potent antioxidant properties. Tocopherols, also, are important components of oil since they possess both antioxidant and vitamin action. One of the characteristics of argan oil is its high content of tocopherols. Indeed, tocopherol levels are at least four times higher in argan oil than in olive oil and two times higher than in hazelnut oil [
Extracts obtained at 300 bar at the three temperatures studied (Table
Supercritical CO2 has proven to be effective in the extraction of oil from
Significant variations were not observed between the physicochemical parameters of freshly obtained argan oil under different extraction conditions of pressure and temperature. The quality of the oil also did not vary significantly on employing SFE, traditional press-extraction or hexane-extraction, systems. Therefore our study provides an evidence that the quality of argan oil extracted by supercritical fluid from
The antioxidant capacity of the argan oil obtained by SFE is high compared with walnut, almond, hazelnut, and peanut oils and is comparable to that determined for pistachio oil. A relationship was found between total tocopherol contents and EC50 values.