Comparative research of Fatty acid Composition and Volatile Components of Fatty oils from seeds of Nigella sativa and Argania spinosa

 

VA Kurkin¹*, AR Mubinov¹, HV Avdeeva¹, TK Ryazanova²

¹Department of Pharmacognosy, Botany and Phytotherapy, Samara State Medical University,

Ulitsa Chapaevskaya 89, Samara, 443099, Russian Federation.

²Research Institute of Hygiene and Human Ecology, Samara State Medical University, Ulitsa Chapaevskaya 89, Samara, 443099, Russian Federation.

 

ABSTRACT:

The falsification of vegetable oils with similar fatty acid composition is an urgent problem, because the replacement of any ingredient can lead to a change in the pharmacological effects and organoleptic properties. This article discusses the identification and comparing of valuable food and cosmetic black cumin — Nigella sativa L. fatty oils from different countries (Egypt, Pakistan, Saudi Arabia) and argan oil (Argania spinosa (L.) Skeels) from Morocco according to the fatty acid composition and content of volatile components. These oils are expensive and valuable, so falsification can be widespread. The fatty acid composition of fatty oils was studied by gas-liquid chromatography (GC-MS). We identified 29 components (fatty acids and terpenoids) in black cumin seed oil and 10 fatty acids in argan seed oil. It was established that oleic acid dominates in the fatty acid profile of the fatty oil of argan seeds, in which besides was observed for the first time 11- eicosenoic acid. It was determined that linoleic acid dominates in the fatty acid profile of the fatty oil of black cumin seeds, in which besides was observed for the first time 11-octadecenoic (vaccenic) acid. In addition, there was shown that the fatty oil of black cumin seeds mainly represented by p-cymol (dominant component in the all samples of oil), β-thujene, longifolen, α-pinene, trans-4-methoxythujone and other terpenoids. The results allows us to recommend the fatty acid profile as criteria of quality of black cumin oil and argan oil.

 

 

 

INTRODUCTION:

Black cumin (Nigella sativa L.) of the Ranunculaceae family is an annual herbaceous plant up to 50cm high¹. Black cumin seeds are widely used in food, cosmetics and medicine. The homeland of black cumin is Southwest Asia and the Mediterranean. Currently black cumin is growing on the Balkan Peninsula, the Caucasus, Asia Minor and Southern Europe. It is cultivated mainly in India, Egypt and the Middle East, in the Western Mediterranean.² There is also the successful experience of the cultivation of this plant in the territory of the Russian Federation.³

 

The genus Nigella L. is widely known throughout the world, however, the degree of the study of some species is characterized by the by incompleteness in the data.

 

The seeds of Nigella sativa L. contain lipolytic enzyme lipase, which is used for the obtaining of several pharmaceuticals.¹ In Russia the seeds of Nigella damascena L. (pharmacopoeial monograph 42-1691-87) are used as a source of the remedy «Nygedaza», which used for the treatment of chronic diseases of the gastrointestinal tract (cholecystopancreatitis, enterocolitis, chronic hepatitis, pancreatitis).^1,3 Nigella sativa L. is registered also as a homeopathic remedy (reg. numb. 95/335/805).³ The Pharmacopoeia of China regulates the quality of Nigella glandulifera L. A great interest has the fatty oil of black cumin seeds for which reported about the antisclerotic, vasodilating, antibacterial and choleretic activities.⁴

 

It is widely also used the fatty oil of the argan tree [Argania spinosa (L.) Skeels], which grows in southwestern Morocco.⁵ This plant is the relic of the Tertiary era and the unique species of the Sapotaceae family.

 

The seeds of the argan tree contain a large amount of fatty oil. The food fatty oil of argan is obtained by cold pressing. The cosmetic argan fatty oil is mainly produced in Europe by extraction with organic solvents.^5,6 It is now frequently referred to as “the world’s most expensive vegetable oil”, which is a symbol of this country.⁷ The argan fatty oil is used in traditional medicine in Morocco as a remedy for dry skin, acne, psoriasis, eczema, wrinkles, joint pain, to prevent hair loss and to treatment of dry hair.⁸

 

By oral administration the argan fatty oil has a choleretic and hepatoprotective effect, and may be effective remedy in preventing of hypercholesterolemia and atherosclerosis.⁹

 

It should be noted that the composition of fatty acids of fatty oils from the seeds of Argania spinosa and Nigella sativa are very similar.

 

Our opinion the falsification of vegetable oils with similar fatty acid composition is an urgent problem, because the replacement of any ingredient, as is known, can lead to a change in the pharmacological effects and organoleptic properties.

 

MATERIALS AND METHODS:

Research samples of the fatty oils:

The objects of this research were 5 commercial samples from different manufacturers and countries (Egypt, Pakistan, Saudi Arabia) of black cumin seed oil and one sample of argan oil from Morocco obtained by cold pressing (samples within the expiration date) in July 2018:

·       Sample No. 1 – Black seeds oil «Egyptian Black Seed Oil» («Organic CO. for Natural oil», Egypt);

·       Sample No. 2 – Black seeds oil «Royal oil» («Hubbet Barack », Egypt);

·       Sample No. 3 – Black seeds oil «Black seeds oil» («Hemani», Pakistan);

·       Sample No. 4 – Black seeds oil «Huile de Nigelle» («Contemporary Beauty », Saudi Arabia);

·       Sample No. 5 – Black seeds oil «Ethiopian gold» («Arabian secrets», Egypt);

·       Sample No.6 – Argan oil «Huile d`Argane Cosmetique» (Morocco).

*Some oil names translated from Arabic and Russian into English

 

 

Chemical Characterization by GC-MS

The fatty acid composition of fatty oils from the seeds of Nigella sativa and Argania spinosa was studied by gas-liquid chromatography after converting fatty acids to methyl esters according to the method of GOST 31665-2012 by transesterification with the methanol solution of potassium hydroxide.¹⁴ 0.5g of the fatty oil was placed in a conical flask, dissolved in 10ml of n-hexane, 0.5ml of a 2 M solution of potassium hydroxide in methyl alcohol was added, mixed and for 5 min heated in a boiling water bath (until the solution boils). Next, the hexane layer was separated, moisture was removed using anhydrous sodium sulfate, the sediment was evaporated and dissolved in 0.5ml of n-hexane.

 

The composition of fatty acids was determined using a Maestro 7820/5975 (Interlab, Russia) gas chromatograph with an Agilent 5975 model mass spectrometer and an auto-injector. The analysis was performed using an HP-5ms column 30m × 0.25mm × 0.25μm (stationary phase: 5% diphenyl-95% dimethylsiloxane).

 

The carrier gas (helium) had a flow rate of 1mL/min, split 1: 80 for black cumin and 1;100 for argan oil.

 

The volume of injected liquid samples - 1μL. The temperature of the ion source was 150ºC, of the quadrupole was 230°C, of the transition chamber - 280 °C. The initial column temperature was 50ºC (1 min) programmed by 15ºC/min until 180°C, then 4ºC/min until 280°C and kept for 5 min.

 

The components were identified by the full mass spectra and linear retention indices. Interpretation of GC-MS mass spectra was conducted using the database of the National Institute Standard and Technology (NIST) library.¹⁵ Only components identified by the library with a probability of more than 90% were considered. Quantitative analysis was carried out over the areas of the corresponding peaks in the chromatogram constructed by the total ion current.

 

RESULTS AND DISCUSSION:

By gas-liquid chromatography-mass spectrometry (GC-MS) there were identified 15 fatty acids in the samples of black cumin seeds oil and 10 fatty acids in argan oil. The unsaturated fatty acids dominate in the fatty acid profile of the oils: on average 88.42% in the samples of black cumin seeds oils and 86.10% in argan oil (the content of some fatty acids varied in individual samples).

 

The valuable essential fatty acids (omega-3 and omega-6) in the samples of black cumin seed oils are mainly represented by linoleic (C_18:2) (W6) and eicosadienoic (C_20:2) (W6) acids, and in the some samples was detected omega-3 linolenic acid (C_18:3). In argan oil, essential fatty acids are represented by omega-6 linoleic acid (C_18:2). In all oil samples, omega-9 acids like oleic (C_18:1) and 11-eicosenoic acid (C_20:1) are also present.

 

According to the content of other components (saturated acids, terpenoids) the differences in the quantitative content were also observed.

 

The essential fatty acids are necessary for the body to function, but due to the lack of suitable enzymes, they can’t be synthesized during metabolism. They should come with food in the form of ready-made structural elements. These metabolites are omega-3 and omega-6 acids, to a lesser extent omega-9.

 

In the 1st sample of black cumin seed oil («Egyptian Black Seed Oil», Egypt) linoleic acid (64.08%), oleic acid (23.32%), mono- and double-unsaturated fatty fatty acids, respectively were detected. The third and fourth main fatty acids found in this sample are palmitic (9.26%) and stearic acid (1.30%). These two latter acids are saturated fatty acids. Linolenic (C_{18: 3}) and behenic (C_{22: 0}) acids, which are identified in other samples of black cumin oil (No. 2 and No. 3), were not detected, but the presence of pentadecylic acid (C_{15: 0}) was detected, and unlike other oil samples, the presence of heptadecenoic acid (C_{17: 1}) in a minor amount.

 

In the 2nd sample («Royal oil», Egypt) it was found that the ratio of linoleic acid (C_{18: 2}) and oleic acid (C_{18: 1}) is different from other samples. About 36.64% of linoleic and 55.84% of oleic acids were found in this sample. In addition, it was revealed a lower content of palmitic acid (3.97%) and the absence of 11-octadecenoic (vaccenic) acid.

 

The samples No. 3, 4 and 5 are very similar in composition of fatty acids. In the third sample “Black Seed Oil” (Pakistan) the content of linoleic acid (C_{18: 2}), oleic acid (C_{18: 1}) and palmitic acid (C_16:0) is 63.33%, 26.56% and 6,41%, respectively (Figure 1). In the 4th sample “Huile de Nigelle” (Egypt) palmitoleic (C_{16: 1}), margarine (C_17:0), linolenic (C_18:3), 11-eicosenoic (C_20:1), arachinic (C_20:0) and behenic acids (C_22:0) there were not found. It was determined that the content of the linoleic acid, oleic acid and palmitic acid is 48.92%, 31.53% and 12,36%, respectively. It was established that the in the 5th sample “Ethiopian gold” (Egypt) the content of linoleic acid and oleic acid is 64.82% and 24.09%, respectively, but the presence of linolenic acid (C_18:3) was not found.

 

The main profile of argan oil «Huile d`Argane Cosmetique» (sample No. 6, Morocco) in the chromatogram is created by unsaturated acids, namely linoleic (32.5%), oleic (53.6%) acids, and by saturated acids: palmitic acid (10.1%), stearic acids (3.44%) (Figure 2).

 

Figure 1: Chromatogram of black cumin seed oil

(“Black seed oil”, Pakistan).

 

Figure 2: Chromatogram of argan oil («Huile

d`Argane Cosmetique», Morocco).

 

The content of fatty acids such as 11-eicosenoic and arachinic acid is 0.12% and 0.10% respectively. The fatty acids such as myristic acid (С_14:0), pentadecanoic acid (С_15:0), palmitoleic acid (С_16:1) and behenic (C_22:0) acid contain in the sample No. 6 in the minor amounts (Table 1).

 

The second black cumin seed oil sample («Royal oil», Egypt) is clearly different in fatty acid composition from other samples. It is known, that the place where the plant grows also influences on the fatty acid composition, but in this case it is clearly different from sample No. 5 («Ethiopian gold», Egypt), which is also from Egypt. Therefore, we consider it separately and are not included in the calculations.

 

In addition, our results we compared with studies by other researchers.^7,10-13 The general ratio of acids is correlated with literature data. However, the interval of individual acids has slightly different values. In contrast to the literature, we found in all samples of black cumin seed oil eicosadienoic (C_{20: 2}), 11-eicosenoic (C_{20: 1}), 11-octadecenoic (vaccenic) (C_{18: 1}) acids (Table 2), and in argan oil was observed 11- eicosenoic acid (C_{20: 1}) (Table 3).

 

Table 1: Variation fatty acid composition of N. sativa seeds oils and argan oil, %.

No.	Rt	Fatty acids	N. sativa seeds oils	Argan oil
1	12.56	Myristic (C14:0)	0.04 – 0.25	0.04
2	13.91	Pentadecanoic (C15:0)	0.01 (No. 1)	0.01
3	15,12	Palmitoleic (C16:1)	0.06 – 0.08 (No. 1–3, 5)	0.02
4	15.48	Palmitic (C16:0)	6.41 – 12.36; No. 2 – 3,97	10.10
5	16.73	Heptadecenoic (C17:1)	0.01 (No.1)	–
6	17.13	Margarinic (C17:0)	0.02 (No. 1, 3, 5)	–
7	18.48	Linoleic (C18:2)*	48.92 – 64.82; No. 2 – 36.64	32.50
8	18.58	Oleic (C18:1)*	23.32 – 31.53; No. 2 – 55,84	53.60
9	18.61	11-оctadecenoic (vaccenic) (C18:1)*	0.45 – 1.79 No. 2 – none	–
10	18.69	Linolenic (C18:3)	0.02 (No. 3), 0.24 (No. 2)	–
11	18.97	Stearic (C18:0)	1.30 – 2,62; No. 2 – 1,24	3.44
12	22.09	Eicosadienoic (C20:2)*	0.61 – 1.48; No 2. – 0,19	–
13	22.17	11-eicosenoic (C20:1)	0.10 – 0.24	0.12
14	22.64	Arachidic (C20:0)	0.06 – 0.16 (No. 1–3, 5)	0,10
15	26.33	Behenic (C22:0)	0.04 – 0.11 (No. 2, 3, 5)	0,02
Total unsaturated fatty acids:			88.42*	86.10

*oil sample No. 2 («Royal oil», Egypt) not considered

 

Table 2: Percentages of fatty acid composition of black cumin seed oils described by other researchers

The main fatty acid composition	Morocco10	Turkey11	Germany12	Our research
Linoleic acid (C18:2)	58.5	57	57.3	48.92-64.82
Oleic acid (С18:1)	23.8	22.8	22.8	23.32-31.53
Palmitic acid (С16:0)	13	12.5	12.5	6.41-12.36
Stearic acid (С18:0)	2.3	3.1	3,1	1.3-2.62
Eicosadienoic acid (С20:2)	-	-	2.44	0.61-1.48
11-eicosenoic acid (С20:1)	-	0.25	0.3	0.1-0.24
11-оctadecenoic (vaccenic) (C18:1)	-	-	-	0.45-1.79

 

Table 3: Percentages of fatty acid composition of argan oil described by other researchers

The main fatty acid composition	Moroccо7	Spain13	Our research
Linoleic acid (C18:2)	29-36	31.26-40,41	32.5
Oleic acid (С18:1)	43-49	36.57-46,73	53.6
Palmitic acid (С16:0)	11-15	12.06-13.94	10.1
Stearic acid (С18:0)	4-7	4.91-8.29	3.44
11-eicosenoic acid (С20:1)	-	-	0.12

 

The research of the oils in these conditions for the content of essential oil components dissolved in them showed their absence in argan oil. The essential oil fraction of black cumin seed oil is mainly represented by p-cymol, which dominates in content for all oil samples (0,09-0,85%),

 

The low content was observed for β-thuyen (0.03-0.07%), longifolen (0.03-0.08%) (present in most samples), and also for α-pinene and trans-4-methoxytujone, which were found in a smaller amount in all fatty oils samples. The β-pinene, thymoquinone, sabinene, limonene, γ-terpinene, cis-4-methoxytuione, terpinen-4-ol (in half of the studied samples), camphor, bornyl acetate, longipinene and apiol contain in minimal amounts. The highest levels of p-cymol (0.85%), α-pinene (0.21%) and trans-4-methoxythujone (0.18%) were observed in sample No. 4 («Huile de Nigelle», Saudi Arabia).

 

CONCLUSION:

The comparison of our results and literature data on the quantitative content of fatty acids allows us to recommend the following fatty acid profile as criteria for the quality of black cumin oil: linoleic acid (C_18:2) should be 48-65% of the total content, 23-32% of oleic acid (С_18:1), 6%-13% of palmitic acid (С_16:0), 1.3-2.7 % of stearic acid (С_18:0), 0.6 %-2.4 % of eicosadienoic acid (С_20:2). As additional quality criteria of the quality of this fatty oil it is advisable to consider the content of 11-eicosenoic and acid 11-оctadecenoic in the interval 0.1-0.24% and 0.45-1.79%, %, respectively.

 

For argan oil we recommend the next criteria of the quality in the composition of fatty acids: the content of linoleic acid (C_18:2) should be 29-40% of the total content, 43-54% of oleic acid (С_18:1), 10%-14% of palmitic acid (С_16:0), 3.4-8.3% of stearic acid (С_18:0) and 11-eicosenoic acid (С_20:1) should be <0.2%.

 

Thus, the black cumin seed oil has more linoleic acid and less oleic acid than argan oil. In the black cumin seed oil 11-оctadecenoic (C_18:1) 0.45-1.79% and eicosadienoic acid (С_20:2) were detected. Argan oil contains more stearic acid (С_18:0) than black cumin seed oil (3.4-8.3%>1.3-2.7%).

 

ACKNOWLEDGEMENTS:

Thanks are due to Director of Research Institute of Hygiene and Human Ecology O. Sazonova, Samara State Medical University, for the equipment provided. Financial support by Samara State Medical University, Samara, for part of this work is acknowledged.

 

CONFLICTS OF INTEREST:

The authors declare no conflicts of interest.

 

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Accepted on 25.06.2020           © RJPT All right reserved

Research J. Pharm. and Tech 2021; 14(3):1586-1590.