Chemical composition of Nigella sativa L. seed extracts obtained by supercritical carbon dioxide

Abstract

Chemical composition of black cumin (Nigella sativa L.) seed extracts obtained by supercritical carbon dioxide at two different conditions that result in total extract (28 MPa/50°C, SFE 1) and major volatile part (12 MPa/40°C, SFE 2) and essential oil obtained by hydrodistillation of SFE-1 (HD SFE). SFE have been carried out to characterize the compounds and the variation of quinones and phenolics. The extracts were analysed by GC and GC-MS and the presence of phenolic compounds was further confirmed by 2D HSQCT (1)H and (13)C NMR spectroscopy. Forty-seven volatile compounds were detected where sixteen compounds were reported for the first time in the oil of this seed. Moreover, thymoquinone (TQ), dithymoquinone (DTQ), thymohydroquinone (THQ) and thymol (THY) were the major phenolic compounds. It can be concluded that the chemical composition of extracts obtained by SC CO2 extraction of the seeds showed better recovery of phenolic compounds than HD SFE and proved the occurrence of thermally labile or photosensitive bioactive volatiles of four major quinonic phenol compounds.

Full text

ORIGINAL ARTICLE
Chemical composition of Nigella sativa L. seed extracts
obtained by supercritical carbon dioxide
Suresh Kumar Tiruppur Venkatachallam &
Hajimalang Pattekhan &Soundar Divakar &
Udaya Sankar Kadimi
Revised: 11 June 2010 / Accepted: 26 September 2010 / Published online: 1 November 2010
#Association of Food Scientists & Technologists (India) 2010
Abstract Chemical composition of black cumin (Nigella
sativa L.) seed extracts obtained by supercritical carbon
dioxide at two different conditions that result in total extract
(28 MPa/50°C, SFE 1) and major volatile part (12 MPa/
40°C, SFE 2) and essential oil obtained by hydrodistillation
of SFE-1 (HD SFE). SFE have been carried out to
characterize the compounds and the variation of quinones
and phenolics. The extracts were analysed by GC and GC-
MS and the presence of phenolic compounds was further
confirmed by 2D HSQCT
1
H and
13
C NMR spectroscopy.
Forty-seven volatile compounds were detected where
sixteen compounds were reported for the first time in the
oil of this seed. Moreover, thymoquinone (TQ), dithymo-
quinone (DTQ), thymohydroquinone (THQ) and thymol
(THY) were the major phenolic compounds. It can be
concluded that the chemical composition of extracts
obtained by SC CO
2
extraction of the seeds showed better
recovery of phenolic compounds than HD SFE and proved
the occurrence of thermally labile or photosensitive
bioactive volatiles of four major quinonic phenol compounds.
Keywords Nigella sativa .Supercritical CO
2
.GC-MS .2D
HSQCT NMR .Thymoquinone
Introduction
A large number of medicinal plants and their purified
constituents have been shown beneficial therapeutic poten-
tials. Seeds of Nigella sativa (black cumin), a dicotyledon
of the Ranunculaceae family, have been used for thousands
of years as a spice and food preservative. Black cumin is an
annual herbaceous plant widely grown in the Mediterranean
countries, Middle East, Eastern Europe and Western Asia.
The seeds have been added as a spice to a variety of Persian
foods such as bread, yogurt, pickles, sauces and salads
(Hajhashemi et al. 2004). In the Middle East, Northern
Africa and India, it has been used traditionally for centuries
for the treatment of asthma, cough, bronchitis, headache,
rheumatism, fever, influenza and eczema and for its
antihistaminic, antidiabetic and anti-inflammatory activities
(Burits and Bucar 2000).
The oil and the seed constituents, in particular
thymoquinone (TQ), have shown potential medicinal
properties; they exhibit potent anti-inflammatory effects
on several inflammation-based models including experi-
mental encephalomyelitis, colitis, peritonitis, oedama,
and arthritis through suppression of the inflammatory
mediators prostaglandins and leukotriens (Chakrabarty et al.
2003). The oil and active ingredient of TQ showed beneficial
immunomodulatory properties, augmenting the T cell and
natural killer cell-mediated immune responses (Haq et al.
1999). Most importantly, both the oil and its active
ingredients expressed anti-microbial and anti-tumor proper-
ties toward different microbes and cancers (Topozada et al.
Electronic supplementary material The online version of this article
(doi:10.1007/s13197-010-0109-y) contains supplementary material,
which is available to authorized users.
S. K. Tiruppur Venkatachallam :U. S. Kadimi (*)
Food Engineering Department, Central Food Technological
Research Institute, (Council of Scientific and Industrial Research),
Mysore 570 020 Karnataka, India
e-mail: udaya@cftri.res.in
H. Pattekhan :S. Divakar
Fermentation Technology and Bioengineering Department,
Central Food Technological Research Institute,
(Council of Scientific and Industrial Research),
Mysore 570 020 Karnataka, India
J Food Sci Technol (Nov–Dec 2010) 47(6):598–605
DOI 10.1007/s13197-010-0109-y

1965; Badary et al. 1999). Coupling these beneficial
effects with its use in folk medicine, Nigella sativa seed is
a promising source for active ingredients that would be
with potential therapeutic modalities in different clinical
settings. More than 150 studies have been conducted and
confirmed the pharmacological effectiveness of Nigella
sativa seed constituents. Though, Nigella sativa seed is a
complex substance of more than 100 compounds, some of
which have not yet been identified or studied (Salem
2005).
TQ, derived from the medicinal spice Nigella sativa has
been shown to exhibit anti-inflammatory (Mutabagani and
El-Mehdy 1997) and anti-cancer activities (Worthen et al.
1998). TQ in nanoparticles were more potent than TQ in
suppressing proliferation of colon cancer, breast cancer,
prostate cancer, and multiple myeloma cells and also that
encapsulation of TQ enhances its anti-proliferative, anti-
inflammatory, and chemosensitizing effects (Ravindran et
al. 2010). Several components of black cumin have been
identified, including thymoquinone, thymol, thymohydro-
quinone, and dithymoquinone (Morikawa et al. 2004). The
most abundant component of black seed oil, TQ has been
reported to exhibit antioxidant (Mansour et al. 2002;
Badary et al. 2003,2007), anti-inflammatory, chemosensi-
tization and chemopreventive potential effects (Badary et
al. 1999; Badary and Gamal El-Din 2001; Gali-Muhtasib et
al. 2004).
Beneficial effects of Nigella sativa (NS) and TQ on
histopathological changes of sciatic nerves in streptozotocin
(STZ) induced diabetic rats were studied. The treatment
with both NS and TQ caused sharp decrease in the
elevated serum glucose, and an increase in the lowered
serum insulin concentrations, in STZ induced diabetic
rats. No histopathological changes of sciatic nerves in
STZ induced diabetic rats by NS and TQ treatment have
been reported (Kanter 2008).
Despite the availability and use of numerous anti-
epileptic drugs, nearly 15% of childhood epilepsy cases
are resistant to treatment. However, in traditional medi-
cine, Nigella sativa has been known for its anticonvulsant
effects. In this double-blinded crossover clinical trial
conducted on children with refractory epilepsy, the
aqueous extract of black seed was administered as an
adjunct therapy and the effects were compared with those
of a placebo. It can be concluded that the water extract of
Nigella sativa has antiepileptic effects in children with
refractory seizures (Akhondian et al. 2007).
TQ converted to DTQ via photodimerization, as a
consequence of exposure to heat and sunlight during
separation and extraction procedures. Various storage
conditions are also expected to make a difference in the
amounts of the quinone constituents especially TQ of the
oil (El-Dakhakhny 1963).
SFE is an attractive alternative to conventional methods
due to its use of environmentally compatible fluids, reduced
solvent consumption, oxygen-free extraction environment,
the ease of separation of solute from supercritical fluid
(SCF) solvent by simple expansion and shorter extraction
time. Supercritical fluid extraction (SFE) of bioactive
compounds from plant material is a promising field for
the industrial application of SFE, since it has many
advantages over steam-distillation and solvent extraction
as it prevents the transformation of bioactive compounds
during extraction. Supercritical CO
2
extraction has been
considered as a possible applied field of SFE, because CO
2
is nontoxic and nonflammable, the lack of a chemical
residue problem and low critical temperature (31.2°C) is
important (Machmudah et al. 2005).
Currently, black cumin seeds have been extensively
studied particularly, which justifies its broad traditional
therapeutic and nutritional value. In consideration of
potential utilization, detailed knowledge on the chemical
composition of the seed is of major importance for food and
pharmaceutical industries. The reason might be found in the
complex chemical composition of the seeds. SC CO
2
technology has provided an impetus for their improvement
in terms of quality as well as quantity of the extracted
bioactive compounds than other conventional extractions.
Thus the SC CO
2
technology described here may find
utility as a superior technology for determine the compo-
sition of pharmacologically active quinones in this N.sativa
seed oil. The aim of the present study was to explore the
chemical composition of extracts isolated from Nigella
sativa seeds by Supercritical CO
2
besides identifying all the
compounds present in the volatile oils by GC MS and NMR
Spectroscopy.
Materials and methods
Plant material Seeds of Nigella sativa were obtained from
Supreem Pharmaceuticals Mysore Pvt. Ltd, Mysore, India.
A voucher specimen authenticated and has been deposited
at the Central Food Technological Research Institute,
Mysore. The seeds were stored in polythene bags and
maintained at 4°C until extraction. Seeds material was dried
and ground into a fine powder using an IKA-10 mini
laboratory mill.
Chemicals Sodium sulphate (anhydrous) and silica gel (60–
120 mesh) for column chromatography was purchased from
SD Fine Chemicals, India. Silica gel G for thin layer
chromatography was purchased from Loba Chemicals,
India. All the solvents used were of analytical grade and
dimethyl sulfoxide (DMSO-d
6
) from Merck Co, Mumbai,
India. The solvents were distilled once before use. For the
J Food Sci Technol (Nov–Dec 2010) 47(6):598–605 599

Table 1 Chemical composition (%) of black cumin seed extracts isolated by supercritical CO
2
extraction
Compound RI
exp
RI
lit
SFE 1 SFE 2 HD SFE Identification
n-Nonane
a
905 900 0.12 ── ── RI, MS
Tricyclene 926 926 tr ── ── RI, MS
Camphene 953 953 ── ── 1.64 RI, MS
β-Pinene 958 959 ── ── 0.40 RI, MS
2,4,(10)-Thujadiene 967 960 4.74 0.19 ── RI, MS
Sabinene 978 977 1.05 ── ── RI, MS
β-Myrcene 990 991 0.31 ── ── RI, MS
1,8-Cineole 1013 1010 ── ── 0.98 RI, MS
α-Terpinene 1025 1026 2.34 ── ── RI, MS
Limonene 1034 1034 0.18 0.38 1.03 RI, MS
γ-Terpinene 1054 1056 27.46 13.20 12.87 RI, MS
cis-Sabinene hydrate 1063 1068 ── 0.38 tr RI, MS
allo-Ocimenol
a
1079 1071 ── 0.11 ── RI, MS
Linalool 1087 1080 0.25 0.19 ── RI, MS
Terpinolene 1091 1088 ── ── tr RI, MS
trans-Sabinene hydrate 1099 1097 0.37 ── ── RI, MS
Terpinen-1-ol
a
1124 1120 ── ── 0.11 RI, MS
1,5,8-p-Menthatriene
a
1130 1135 0.43 0.38 ── RI, MS
Borneol 1152 1152 ── ── 1.02 RI, MS
Pinocarvone 1167 1165 2.96 3.00 ── RI, MS
trans-Dihydrocarvone 1208 1202 ── 0.19 ── RI, MS
Dihydrocarvone
a
1215 1214 0.37 2.06 ── RI, MS
Ocimenone (E)
a
1249 1239 1.54 1.50 ── RI, MS
Thymoquinone 1250 1250 35.05 33.12 38.41 RI, MS,NMR
Thymol 1283 1288 7.43 5.30 16.95 RI, MS,NMR
Carvacrol 1299 1299 1.98 1.73 0.81 RI, MS
2-Undecanone 1312 1315 ── ── 13.72 RI, MS
n-Octyl isobutyrate
a
1323 1326 ── ── 0.12 RI, MS
α-Longipinene 1330 1334 0.26 ── ── RI, MS
Citronellyl acetate
a
1339 1336 ── ── 0.50 RI, MS
Thymohydroquinone methyl ether
a
1353 1351 ── ── tr RI, MS
Cyclosativene 1367 1366 ── ── 1.43 RI, MS
α-Longicyclene 1381 1380 0.43 5.25 ── RI, MS
α-Copaene 1385 1383 1.54 2.00 0.41 RI, MS
α-Longifolene 1391 1387 ── ── 0.51 RI, MS
(Z)-Caryophyllene
a
1395 1395 0.23 ── ── RI, MS
β-Caryophyllene 1420 1417 2.89 5.07 4.80 RI, MS
Thymohydroquinone dimethylether
a
1429 1425 0.43 ── ── RI, MS
Aromadendrene
a
1437 1438 ── ── 1.04 RI, MS
Thymohydroquinone 1515 1509 1.17 1.12 2.31 RI,MS,NMR
Davanone
a
1587 1586 0.31 ── ── RI, MS
8-Heptadecene
a
1683 1680 1.23 1.13 0.86 RI, MS
Dihydrofarnesyl acetate
a
1841 1840 2.28 4.69 ── RI, MS
Pimaradiene
a
1934 1935 1.23 2.25 ── RI, MS
Palmitic acid 1947 1946 0.18 ── ── RI, MS
Pimara-8(14),15-diene 1968 1966 0.92 ── ── RI, MS
Octadecanoic acid 2145 2157 0.26 12.31 ── RI, MS
Total identified 99.94 95.55 99.92
Grouped compounds:
600 J Food Sci Technol (Nov–Dec 2010) 47(6):598–605

determination of retention indices, a hydrocarbon mixture
(Sigma, India) ranging from n-octane to n-docosane was
used. Food grade CO
2
cylinder (99.9% purity) was
obtained from Kiran Corporation, Mysore, India.
Supercritical fluid extraction A Nova Swiss high pressure
extractor (Nova Werke, AG, model Ex 1000–1.4–1.2) was
used for the extractions. Food grade CO
2
was pumped
into the system by diaphragm pump until the required
pressure was obtained. Back pressure regulators were used
to set the system pressure (in extractor and separator). The
extractor vessel was loaded with 1 kg of the powdered
material of black cumin seeds. Heat exchangers were
provided in the system and on the extractor and separator
vessel for temperature elevation. SC CO
2
flows through
the extractor and enters the separator vessel through an
expansion valve and was re-circulated. Samples of the
extracted substance were collected by opening the valve
located at the bottom of the separator vessel. A flow meter
was provided to monitor the flow rate of CO
2
circulating
in the system. Extractions were carried out at two different
conditions of pressures and temperatures, namely 28 MPa
at 50°C (SFE 1) and 12 MPa at 40°C (SFE 2) at a CO
2
mass flow rate of 3.3–8.05×10
−4
kg/s (Udaya Sankar
1989).
Hydrodistillation The Supercritical CO
2
extract (SFE 1)
was subjected to hydrodistillation (HD) for 6 h using a
Clevenger-type apparatus. The essential oil (HD SFE)
obtained was yellow color with aromatic odour in a yield
of 1.5% (v/v) which was dried using anhydrous sodium
sulphate and then stored at 4°C in dark until analysis.
Column chromatography 5mlofSFE1samplewas
subjected to purification, using a glass column (40 mm
i.d×450 mm length) packed with silica gel (60–120
mesh) and eluted with hexane and ethyl acetate at 99:1
ratio. Fractions of volume 250 ml were collected and
concentrated. They were monitored by TLC in 9:1 ratio
of hexane and ethyl acetate. The spots were located by
exposing the plates to iodine vapours. Fractions having
the similar pattern of the spots with similar Rf values on
the TLC plates were collected and pooled. From
chromatographic separation, four fractions were detected.
The fraction weights were: fraction 1; 1.3 L, fraction 2;
0.8 L, fraction 3; 0.4 L and fraction 4; 0.7 L.
GC and GC-MS analysis GC analyses were performed
using a Fisons GC 8000 gas chromatograph equipped with
FID detector. All the analyses were carried out by a fused
silica DB-5MS column (30 m× 0.32 mm i.d., film thickness
0.25 μm). The oven temperature was increased from 70°C
to 220°C at 4°C min and held isothermal for 15 min.
The injector and detector temperatures were maintained at
220°C and 240°C respectively. 10% of samples were
prepared in chloroform. The injection volume was 0.5 μL
with a split ratio of 1:30 and nitrogen used as carrier gas at
a flow rate of 1 ml/min. GC-MS recordings were made on a
Shimadzu gas chromatograph (Shimadzu, Japan) coupled
with QP-5000 mass spectrometer. A 0.5 μL sample was
injected in the split mode ratio of 1:15. Helium was used as
carrier gas at a flow rate of 1 ml/min. All the other
parameters remained unchanged relative to GC analyses.
Mass spectra were obtained by EI at 70 eV. Mass scanning
was performed from 40 to 400 amu.
Table 1 (continued)
Compound RI
exp
RI
lit
SFE 1 SFE 2 HD SFE Identification
Quinones 44.08 39.54 57.67
Monoterpene hydrocarbons 36.51 14.15 15.94
Oxygenated monoterpenes 7.47 9.16 17.14
Sesquiterpene hydrocarbons 5.35 12.32 8.19
Oxygenated sesquiterpenes 2.59 4.69 ──
Diterpenes 2.15 2.25 ──
Alkane 0.12 ── ──
Alkenes 1.23 1.13 0.86
Fatty acids 0.44 12.31 ──
Fatty acid esters ── ── 0.12
Identification has been through by comparing mass spectra (MS), retention indices (RI), NMR spectra, data from NIST, Wiley commercial
libraries, Chemistry Web Book (www.nist.org/chemistrywebbook) and other reports (Joulain and Konig 1998; Adams 2007)
SFE 1 (28 MPa/50°C), SFE 2 (12 MPa/40°C) and hydrodistillation of SFE 1 (HD SFE)
The retention indices were calculated for all compounds using a homologous series of C
8
-C
22
n- alkanes. RI
exp
, experimental retention indices
given for DB-5MS column; RI
lit
, literature retention indices given for DB-5MS column. tr, trace (<0.1%)
a
Compounds identified for the first time in the extracts of Nigella sativa
J Food Sci Technol (Nov–Dec 2010) 47(6):598–605 601

1
H and
13
C NMR analysis Two-dimensional Heteronuclear
Single Quantum Coherence Transfer Spectra (2D HSQCT)
were recorded using a Bruker Avance AQS 500 MHz
(Bruker Biospin, Fallanden, Switzerland) NMR spectrom-
eter operating at 500.18 MHz for
1
H and 125.78 MHz
for
13
C at 20°C. Proton and carbon 90° pulse widths were
12.25 and 10.5 μs, respectively. Chemical shifts were
expressed in ppm relative to tetramethylsilane (TMS) as an
internal standard. 5 mg of samples dissolved in DMSO-d
6
was used for recording the spectra in magnitude mode with
sinusoidal-shaped z-gradients of strength 25.7, 15.42 and
20.56 G/cm with a gradient recovery delay of 100 μsto
defocus unwanted coherences. Increment of t1 was in 256
steps. About 50–200 scans and 500–6000 scans were
accumulated with a recycle period of 2–3 seconds to obtain
good spectra for
1
H and
13
C NMR, respectively. A region
from 0–10 ppm and 0–200 ppm were scanned for all the
samples for
1
Hand
13
C NMR, respectively. The size of the
computer memory used to accumulate the data was 4 kB.
The spectra were processed using unshifted and π/4 shifted
Fig. 1 Structures of thymoqui-
none, thymohydroquinone,
thymol and dithymoquinone
Table 2
1
H and
13
C 2D-HSQCT NMR data of compounds 1, 2 and 3
a
in DMSO-d
6
Carbon number Chemical shifts (ppm) Compound 1 Chemical shifts (ppm) Compound 2 Chemical shifts (ppm) Compound 3
1
H NMR (J in Hz)
13
C NMR
1
H NMR (J in Hz)
13
C NMR
1
H NMR (J in Hz)
13
C NMR
1── 145.1 ── 127.2 ── ──
2 6.59(s) 133.5 (i1) 7.03 (s) 120.4 6.72 (s) 133.5 (i1)
3── 188.3 (i2) ── ── 7.47 (d, 8 Hz) 127.9 (i2)
4── 187.3 (i2) ── ── ── 154.1
5 6.72(s) 133.3 (i1) 5.30 (s) 129.3 7.85 (d, 8 Hz) 125.8 (i1)
6── 156.4 ── 133.5 ── 127.7 (i2)
7── 14.9 ── 14.3 ── 14.2
8 2.12 (m, 5.3 Hz) 31.0 1.92 (m, 5.1 Hz) 31.1 2.01 (m, 5.4 Hz) 30.8
9 1.93 (d, 5.3 Hz) 26.7 1.41 (d, 5.1 Hz) 24.5 1.37 (d, 5.4 Hz) 23.5
10 1.94 (d, 5.3 Hz) 26.7 1.47 (d, 5.1 Hz) 25.3 1.41 (d, 5.4 Hz) 26.2
a
5 mg of sample was dissolved in 0.5 ml of DMSO-d
6
for recording the spectra at 20°C on Bruker Avance AQS 500 MHz NMR spectrometer. All the
details are mentioned in Materials and Methods. s-singlet, d-doublet, m-multiplet and i-interchangeable
602 J Food Sci Technol (Nov–Dec 2010) 47(6):598–605

sine bell window function in F1 and F2 dimensions,
respectively.
Compounds identification Compounds were identified
based on comparison of their Kovats retention indices
(RI) relative to C
8
-C
22
n-alkanes and matching of the mass
spectra with those detailed in the NIST, Wiley commercial
libraries, data from Chemistry web book and literature data
(Joulain and Konig 1998; Adams 2007).
Results and discussion
The SFE 1 extract carried out at pressure of 28 MPa and
temperature of 50°C resulted in total extract yield of
26.02% contained both volatile and nonvolatile fraction.
The SFE 2 extract found to contain a major fraction of
steam volatile components only at lower pressure and
temperature of extraction (Udaya Sankar 1989). In this
study, extract yield is expressed in % and defined as weight
of the extract divided by weight of the sample. SFE1
obtained higher extract yield than the SFE 2. The extraction
yield was increased with increasing pressure and tempera-
ture at certain levels along with better recovery of quinones
and phenolics. The hydrodistillation of Nigella sativa seed
powder with Clevenger distillation yielded 1.0–1.2% of
essential oil with 30–32% of thymoquinone (TQ). In SFE 1,
the extract yield was 26.02% with 7.11% of TQ whereas in
SFE 2 the yield of extract was 7.8% with TQ content of
12.27%. The recovery of TQ on the seed basis was 0.4–
0.5% in hydrodistillation, 1.85% in SFE 1 and 0.95% in
SFE 2. Hence, by SC CO
2
extraction the recovery of TQ
was much better.
Hydrodistillation of SFE 1 extract yielded 1.5% of essential
oil (HD SFE) with characteristic transparent yellow color with
typical aromatic odour. A total of 47 different compounds
were identified in Nigella sativa seed oils extracted by
supercritical CO
2
(SFE 1 and SFE 2) and hydrodistillation of
SFE 1 (HD SFE). About 31 compounds were identified in
SFE 1 oil, 22 compounds in SFE 2 oil and 23 compounds in
HD SFE oil. Among the 47 compounds, the occurrences of
16 volatile compounds were reported for the first time in
Nigella sativa seeds (Table 1). They are n-nonane,
allo-ocimenol, terpinen-1-ol, 1,5,8-ρ-menthatriene, dihydro-
carvone, ocimenone (E), n-octyl isobutyrate, citronellyl
acetate, thymohydroquinone methyl ether, (Z)-caryophyllene,
thymohydroquinone dimethyl ether, aromadendrene, dava-
none, 8-heptadecene, dihydro farnesyl acetate and pimara-
diene. The lower number of compounds occurred in HD SFE
compared to SFE is mainly related to the possible degradation
of volatile compounds by higher temperature and longer
distillation time.
The SFE oils could be distinguished from the HD SFE
oil by their greater richness in monoterpene hydrocarbons
(36.51% in SFE 1, 14.15% in SFE 2 and 15.94% in HD
SFE), sesquiterpene hydrocarbons (5.35% in SFE 1,
12.32% in SFE 2 and 8.19% in HD SFE), oxygenated
sesquiterpenes (2.59% in SFE 1 and 4.69% in SFE 2),
diterpenes (2.15% in SFE 1 and 2.25% in SFE 2), fatty
acids (0.44% in SFE 1 and 12.31% in SFE 2) and fatty acid
esters (0.12% in HD SFE). The oxygenated monoterpenes
were more represented in HD SFE (17.14%) than in SFE 1
(7.47%) and SFE 2 (9.16%). Quinones were present to
greater extent in HD SFE (57.67%) than SFE 1 (44.08%)
and SFE 2 (39.54%) oils. The main compounds in SFE 1,
SFE 2 and HD SFE oils were thymoquinone (35.05% in
SFE 1, 33.12% in SFE 2 and 38.41% in HD SFE),
γ-terpinene (27.46% in SFE 1, 13.20% in SFE 2 and
12.87% in HD SFE), thymol (7.43% in SFE 1, 5.30% in
SFE 2 and 16.95% in HD SFE), β-caryophyllene (2.89% in
SFE 1, 5.07% in SFE 2 and 4.80% in HD SFE) and
thymohydroquinone (1.17% in SFE 1, 1.12% in SFE 2 and
2.31% in HD SFE). In this study, dithymoquinone (DTQ)
could not be traced by GC and GC-MS analysis of these
Table 3
1
H and
13
C 2D-HSQCT NMR data of compound 4
a
in
DMSO-d
6
Carbon number Chemical shifts (ppm) Compound 4
1
H NMR (J in Hz)
13
C NMR
1── 59.7 (i1)
2 4.59 (s) 59.4 (i1)
3── 172.9 (i2)
4── 192.7 (i2)
5 5.40 (s) 129.8 (i3)
6── 154.1 (i4)
7── 59.6 (i1)
8 4.02 (s) 59.4 (i1)
9── 172.9 (i2)
10 ── 192.7 (i2)
11 5.40 (s) 130.3 (i3)
12 ── 153.0 (i4)
13 1.07 (s) 22.0 (i5)
14 1.06 (s) 20.9 (i5)
15 2.27 (m, 5.3 Hz) 33.6
16 1.18 (d, 5.3 Hz) 29.2
17 1.17 (d, 5.3 Hz) 29.1
18 2.26 (m, 5.5 Hz) 33.4
19 1.16 (d, 5.5 Hz) 28.6
20 1.15 (d, 5.5 Hz) 28.5
a
5 mg of sample was dissolved in 0.5 ml of DMSO-d
6
for recording the
spectra at 20°C on Bruker Avance AQS 500 MHz NMR spectrometer. All
the details are mentioned in Materials and Methods. s-singlet, d-doublet,
m-multiplet and i-interchangeable
J Food Sci Technol (Nov–Dec 2010) 47(6):598–605 603

oils, as confirmed by Burits and Bucar (2000) and Benkaci-
Ali et al. (2007). The present analysis showed higher
thymoquinone content than what has been reported in the
literatures so far (Burits and Bucar 2000; El-Ghorab 2003).
Fractions obtained from column chromatography sepa-
ration, showed a mixture of four quinonic phenol com-
pounds, all possessing the thymol skeleton through 2D
HSQCT NMR spectra in different proportions.
Compound 1 showed the presence of two carbonyl
groups at 187.3 ppm and 188.3 ppm. Further, two aromatic
protons were detected at 6.59 ppm and 6.72 ppm. A CH
3
group attached to an aromatic ring was detected at
14.9 ppm in the carbon spectrum. The presence of
isopropyl group was detected by observing signals at
1.93 ppm and 1.94 ppm (doublet) and 2.12 ppm, all with
the coupling constant of 5.3 Hz (Table 2). Thus, compound
1 was identified to be thymoquinone (Fig. 1).
Compound 2 showed methyl groups attached to an
aromatic ring and an isopropyl group attached to an
aromatic ring at 14.3 ppm and 31.1 ppm (
1
H 1.92 ppm),
24.5 ppm (
1
H 1.41 ppm), 25.3 ppm (
1
H1.47ppm)
respectively with a characteristic coupling constant value
of 5.1 Hz. Two aromatic protons were detected at 5.30 ppm
and 7.03 ppm (Table 2). All these showed that compound 2
could be thymohydroquinone (Fig. 1).
Compound 3 showed the characteristic thymol
1
H and
13
C NMR characteristics. Two ortho coupled signals were
detected at 7.47 ppm and 7.85 ppm with a characteristic
ortho coupling constant of 8.0 Hz. A single aromatic peak
was also detected at 6.72 ppm. Phenolic carbon was
observed at 154.1 ppm. An isopropyl group attached to an
aromatic ring (30.8 ppm, 23.5 ppm and 26.2 ppm) was also
observed (Table 2). Thus, compound 3 clearly showed the
characteristic of thymol (Fig. 1).
Two dimentional NMR characteristics of compound 4
showed clearly fusion of two thymoquinone rings with two
alicyclic methyl groups (at 1.07 ppm and 1.06 ppm) along
with two isopropyl groups attached to the quinone ring.
Only two aromatic protons were detected at 5.4 ppm. Four
keto groups were detected at 172.9 ppm and 192.7 ppm
clearly indicating the fusion of two thymoquinone moieties
(Table 3). Thus, compound 4 was identified to be
dithymoquinone (Fig. 1).
This study showed that HD SFE gives an essential oil
of better quality especially in terms of richness in
quinones including better recovery of main compounds
of thymoquinone, γ-terpinene, thymol, β-caryophyllene
and thymohydroquinone than the extracts obtained by SFE
alone. More than 50% of the essential oil compounds of
Nigella sativa were due to thymoquinone and ρ-cymene
(Machmudah et al. 2005). It is interesting to observe that
ρ-cymene was not detected here because the composition
of ρ-cymene in the extract was may be too low. There are
some variations in the qualitative and quantitative compo-
sitions of Nigella sativa essential oil in different regions of
the world. Many factors can influence the essential oil
composition of seeds including genetic and phenologic
stage as well as environment effects and extraction
methods (Reineccius 1994;Omidbaigi1997;Goraetal.
2002).
Conclusion
Sixteen compounds were identified for the first time in
hydrodistillate of SFE and supercritical CO
2
extracts of
Nigella sativa. To our knowledge, this is the first report on
the chemical composition of essential oil obtained by
hydrodistillation of SC CO
2
extract of Nigella sativa seeds.
This study has clearly brought out the possibilities to obtain
higher percentage of valuable volatiles such as thymoqui-
none through the SC CO
2
technology and proved its
superiority to earlier reports in the literature.
Acknowledgement The first author acknowledges the management
and Dr. H. Muhamed Mubarack, Advisor, School of Life Sciences of
the RVS College of Arts and Science, Coimbatore, Tamil Nadu, India
for sponsoring as a Teacher Research Fellow at CFTRI, Mysore. We
thank the Director of the Central Food Technological Research
Institute, (CSIR), Mysore, for providing all the facilities.
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