molecules
Article
Comparison of Volatile Organic Compounds of Sideritis
romana L. and Sideritis montana L. from Croatia
Tihana Marić 1 , Maja Friščić 1, *, Zvonimir Marijanović 2 , Željan Maleš 1
1
2
3
*
Citation: Marić, T.; Friščić, M.;
Marijanović, Z.; Maleš, Ž.; Jerković, I.
Comparison of Volatile Organic
Compounds of Sideritis romana L. and
Sideritis montana L. from Croatia.
Molecules 2021, 26, 5968. https://
doi.org/10.3390/molecules26195968
Academic Editor:
Carmen González-Barreiro
and Igor Jerković 3, *
Department of Pharmaceutical Botany, University of Zagreb Faculty of Pharmacy and Biochemistry,
Schrottova 39, 10 000 Zagreb, Croatia; tihana.vilovic@pharma.unizg.hr (T.M.);
zeljan.males@pharma.unizg.hr (Ž.M.)
Department of Food Technology and Biotechnology, Faculty of Chemistry and Technology, University of Split,
Rud̄era Boškovića 35, 21 000 Split, Croatia; zmarijanovic@ktf-split.hr
Department of Organic Chemistry, Faculty of Chemistry and Technology, University of Split,
Rud̄era Boškovića 35, 21 000 Split, Croatia
Correspondence: maja.friscic@pharma.unizg.hr (M.F.); igor@ktf-split.hr (I.J.)
Abstract: A study on the headspace volatile organic compounds (VOCs) profile of native populations of Sideritis romana L. and Sidertis montana L., Lamiaceae, from Croatia is reported herein, to
elucidate the phytochemical composition of taxa from this plant genus, well-known for traditional
use in countries of the Mediterranean and the Balkan region. Headspace solid-phase microextraction (HS-SPME), using divinylbenzene/carboxene/polydimethylsiloxane (DVB/CAR/PDMS) or
polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber, coupled with gas chromatography-mass
spectrometry (GC-MS) was applied to analyze the dried aerial parts of six native populations in total.
Furthermore, principal component analysis (PCA) was conducted on the volatile constituents with an
average relative percentage ≥1.0% in at least one of the samples. Clear separation between the two
species was obtained using both fiber types. The VOCs profile for all investigated populations was
characterized by sesquiterpene hydrocarbons, followed by monoterpene hydrocarbons, except for
one population of S. romana, in which monoterpene hydrocarbons predominated. To our knowledge,
this is the first report on the VOCs composition of natural populations of S. romana and S. montana
from Croatia as well as the first reported HS-SPME/GC-MS analysis of S. romana and S. montana
worldwide.
Keywords: Sideritis romana; Sideritis montana; terpenes; HS-SPME; GC-MS; bicyclogermacrene;
germacrene D; viridiflorol; principal component analysis
Received: 31 August 2021
Accepted: 28 September 2021
Published: 1 October 2021
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4.0/).
1. Introduction
Essential oils (EOs) are natural, volatile and complex mixtures of lipophilic compounds, often including terpenes, phenol-derived aromatic compounds and aliphatic
compounds, that are biosynthesized by aromatic plants as their secondary metabolites and
represented by a strong odor [1]. Ecologically, they are important for the plant defense
system by providing protection against grazers, taking part in fire and drought tolerance
and attracting pollinators and other animals for seed dispersal. The most often reported
bioactivities of EOs and their components are antimicrobial, antiviral, antinociceptive, anticancer, anti-inflammatory, digestive, semiochemical and free radical scavenging [2], while
new potential applications in human health, nutrition, agriculture and the environment are
continuously emerging [1].
The volatile components of EOs are biosynthesized in specialized secretory structures
such as glandular trichomes located on the surface, or secretory cells and ducts situated
within the tissues of various plant organs of aromatic plants. The conventional techniques
for volatile organic compounds (VOCs) extraction include, e.g., hydrodistillation and steam
distillation, expression (cold pressing), solvent extraction [3] and enfleurage (a classical
Molecules 2021, 26, 5968. https://doi.org/10.3390/molecules26195968
https://www.mdpi.com/journal/molecules
Molecules 2021, 26, 5968
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method for extracting volatile oil from flowers using a layer of animal fat) [4]. Along
with conventional methods used for the extraction of volatile compounds from plants,
solid-phase microextraction (SPME) is considered a convenient alternative technique for
a variety of sample matrices (liquid/solid samples or headspace (HS) vapors). This technique bypasses the distillation or solvent extraction procedure [2]. It uses a fused silica
fiber that is externally coated with an appropriate stationary phase such as polydimethylsiloxane (PDMS), polyacrylate (PA), PDMS/divinylbenzene (DVB), carbowax (CW)/DVB,
and carboxene (CAR)/PDMS on which the headspace VOCs are adsorbed [5]. After the
extraction, the fiber is usually directly inserted into the injector for gas chromatography
analysis usually coupled with mass spectrometry (GC-MS), which is the most often used
technique for the chemical characterization of EOs [2]. SPME has been widely used for
chemical analysis of volatile components of different types of food substances, flavors,
and medicinal plant materials because it is a simple, rapid, inexpensive and solvent-free
technique that demands only a small amount of sample and reduces the degradation of
VOCs [6,7]. Furthermore, headspace solid-phase microextraction (HS-SPME) requires
no sample pre-treatment, allows high selectivity for small compounds and reusability of
various commercially available SPME fibers [8], which makes this technique generally well
accepted for VOCs extraction.
The genus Sideritis L. (family Lamiaceae) includes more than 150 species of annual or
perennial herbs and shrubs, distributed in temperate and tropical regions of the Northern
Hemisphere, with the majority of species found in the Mediterranean area, North Africa,
the Iberian Peninsula, the Middle East and in the Macaronesian region [9–11]. The use of
aerial parts of many Sideritis species has been well reported, especially in Albania, Bulgaria,
Greece, Macedonia and Turkey, where they are consumed as herbal teas and applied in
traditional medicine for the treatment of various disorders of the gastrointestinal and
respiratory system, as well as for burns and wounds [10,12].
In recent decades, many researchers have been trying to justify the traditional uses
of Sideritis species by elucidating their phytochemical composition and investigating potentially useful pharmacological activities of these species [10,13,14]. Although species
from Lamiaceae family are well known for their aromatic properties and are recognized as
the most important source of EOs with economical interest among Angiosperms [3], the
species of the genus Sideritis have been reported as poor in EOs [10,15,16]. Nevertheless,
for the pharmacological activity of Sideritis species, terpenes and flavonoids seem to be
the constituents that are most important. Other chemical components which have been
identified within the genus are iridoids, coumarins, lignans, phenylpropanoid glycosides
and sterols [15].
Only three taxa of this genus are reported to be native to Croatia: Sideritis romana L.,
S. romana L. subsp. purpurea (Talbot ex Benth.) Heywood and S. montana L. [17]. While
several reports on EOs of S. romana L. [18,19], S. romana subsp. purpurea [20,21] and S.
montana L. [18,22–26] isolated by hydrodistillation have already been published, as well as
that of S. romana subsp. purpurea EO constituents obtained by steam distillation [27], the
composition of the headspace volatile components extracted using HS-SPME has never
been evaluated for these species. Furthermore, to the best of our knowledge, the only
report on using the HS-SPME technique for the detection of volatile components within
the genus Sideritis has been published for S. ozturkii Aytac and Aksoy [28]. Additionally,
the volatile HS profiles of S. scardica Griseb. and S. raeseri Boiss. and Heldr. were analyzed
using GC-FID/MS [29], while EO composition of S. albiflora Hub.-Mor. was analyzed by
both HS GC-MS and thermal desorption GC-MS [30].
The aim of the present study was to compare the VOCs composition of the aerial
parts of S. romana L. and S. montana L. populations from different parts of Croatia and
to determine characteristic volatile compounds for each species. Having in mind that
the composition of volatile compounds may vary depending on environmental conditions [31,32], in comparison to similar studies conducted on hydrodistilled EOs of these
species, which were based on the analysis of single populations [18,19,22–26], the advan-
Molecules 2021, 26, 5968
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tage of our study is a greater number of investigated S. romana (four) and S. montana
(two) populations. Considering that, on one hand, Sideritis species are generally poor in
essential oil, and the limited availability of plant material in natural habitats from which the
samples had been collected, and, on the other hand, the multiple advantages of HS-SPME,
which have been mentioned above, instead of the conventionally used hydrodistillation,
the latter technique was chosen for the isolation of volatile components, which were further analyzed by using GC-MS, with the aim to obtain more reliable results. Previous
studies have shown that hydrodistillation and HS-SPME can detect similar major volatile
constituents of individual plant species, although their relative percentages may vary
depending on the technique used [33]. Having in mind that HS-SPME may, among other
things, depend on the type of fiber used for extraction [34], the volatile components were
extracted by HS-SPME using two different fibers suitable for untargeted analysis [35],
divinylbenzene/carboxene/polydimethylsiloxane (DVB/CAR/PDMS) and polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber. To account for possible genetically and/or
ecologically dependent variabilities in VOCs composition, several populations of S. romana
(four populations) and S. montana (two populations) have been included in the analysis
and principal component analysis (PCA) was conducted on the major volatile constituents
(average relative percentage ≥ 1.0% in at least one of the samples) obtained by each fiber
to examine the interrelationships among the investigated populations. Furthermore, the
obtained results have been compared to previous findings for the same two species that
were mostly based on hydrodistillation. Finally, the VOCs profile was compared to related
species and discussed considering the reported biological activities of major constituents.
To our knowledge, this study is the first report on the VOCs profile of natural populations
of S. romana and S. montana from Croatia.
2. Results
2.1. HS-SPME/GC-MS Analysis
2.1.1. DVB/CAR/PDMS Fiber
VOCs of four populations of Sideritis romana and two populations of S. montana
were extracted by HS-SPME, using DVB/CAR/PDMS fiber and their composition was
analyzed by GC-MS. In total, 69 VOCs were identified, accounting for 86.18–90.29% of
the total VOCs content (Table 1). The VOCs compositions of investigated populations of
both investigated species were characterized by sesquiterpene hydrocarbons, followed
by monoterpene hydrocarbons, except for that of S. romana from Morinje Bay (S. romana
M), in which monoterpene hydrocarbons and other compounds were more abundant than
sesquiterpene hydrocarbons. Additionally, for the latter, oxygenated sesquiterpenes were
more represented than in other investigated samples (Figure 1). The main individual
compounds that were identified for S. romana were bicyclogermacrene (15.16–23.04%)
(except S. romana M), trans-caryophyllene (3.60–23.88%) (except S. romana from Kamenjak (S.
romana K) and Blato (S. romana B)), trans-β-farnesene (1.00–12.79%), limonene (1.68–7.58%),
alloaromadendrene (2.35–7.32%), β-pinene (2.61–8.01%), and isocaryophyllene (2.39–4.70%)
(except S. romana M). Exceptionally, for S. romana M, the main identified compounds
were benzyl alcohol (13.28%), viridiflorol (10.29%), ledene (8.20%), limonene (7.10%), βpinene (6.67%), and p-cymene (5.49%). For S. montana, the main identified individual
compounds were germacrene D (17.04–23.23%), trans-caryophyllene (6.56–11.89%), δcadinene (7.57–8.85%), bicyclogermacrene (4.19–11.76%), limonene (6.31–8.14%), and transβ-farnesene (3.56–4.83%) (Table 1).
Molecules 2021, 26, 5968
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Table 1. Volatile organic compounds (VOCs) composition (%) of S. romana and S. montana obtained by HS-SPME/GC-MS
with DVB/CAR/PDMS fiber.
No.
Compound
CD 1
RI 2
S. romana
K
S. romana
B
S. romana
M
S. romana
P
S. montana
J
S. montana
M
1
2
3
4
5
6
7
8
9
10
11
12
13
Acetic acid
Pentanal
Hexanal
(E)-Hex-2-enal
α-Thujene
α-Pinene
Camphene
Benzaldehyde
Hexanoic acid
Sabinene
Oct-1-en-3-ol
β-Pinene
β-Myrcene
(E,E)-Hepta-2,4dienal
α-Phellandrene
α-Terpinene
p-Cymene
Limonene
Benzyl alcohol
Phenylacetaldehyde
γ-Terpinene
Octan-1-ol
α-Terpinolene
Linalool
Nonanal
Benzeneethanol
α-Campholenal
trans-Pinocarveol 3
Pinocarvone
4-Terpineol
Cryptone
α-Terpineol
Myrtenal
Decanal
Verbenone
2-Phenoxyethanol
Carvone
Bicycloelemene
α-Cubebene
α-Copaene
Isoledene
Longifolene
α-Gurjunene
Aristolene
transCaryophyllene
Calarene
Aromadendrene
Alloaromadendrene
Selina-5,11-diene 3
γ-Muurolene
trans-β-Farnesene
Isocaryophyllene
γ-Gurjunene
α-Amorphene
C1
<900
<900
<900
<900
936
944
960
969
975
981
983
985
995
0.15
0.07
0.24
0.47
1.32
0.07
0.44
0.12
0.27
0.60
3.69
0.80
0.85
0.40
0.08
0.13
1.03
0.94
0.07
0.32
0.44
2.61
0.84
3.11
0.52
0.90
1.08
2.51
0.01
2.58
0.21
6.67
1.27
1.33
0.24
0.42
0.21
2.19
0.19
0.71
0.09
8.01
0.88
0.32
0.02
0.14
0.16
3.42
0.07
0.37
0.13
0.13
2.81
0.91
0.55
0.04
0.47
0.05
1.23
0.42
0.09
0.09
0.46
1.52
0.64
1001
-
0.07
0.63
-
0.05
-
C17
C18
1011
1023
1032
1036
1040
1051
1066
1075
1093
1103
1107
1117
1132
1145
1169
1182
1191
1195
1199
1208
1212
1223
1249
1342
1353
1375
1377
1395
1412
1422
0.32
0.62
0.99
6.34
2.96
0.12
1.75
1.37
0.33
0.11
0.17
0.07
0.20
0.60
0.50
0.39
0.16
0.11
0.15
0.12
0.75
0.12
0.18
0.37
0.56
1.17
1.08
3.37
0.61
1.81
7.58
3.82
0.98
2.22
0.52
0.26
0.07
0.13
0.36
0.23
0.95
0.20
3.85
0.54
0.10
0.15
0.06
0.53
0.29
0.34
0.95
0.91
2.54
1.32
5.49
7.10
13.28
3.67
3.55
0.34
0.42
0.77
0.71
0.89
1.25
1.03
0.61
-
0.20
0.38
1.32
1.68
3.84
1.40
2.50
0.05
0.19
0.40
0.31
0.15
0.02
0.47
0.23
0.40
0.23
0.28
0.85
-
0.10
0.07
0.04
8.14
0.84
0.08
0.35
0.08
0.04
0.05
0.04
0.22
0.56
1.67
0.34
0.37
0.12
-
0.09
0.07
0.05
6.31
2.14
0.09
0.08
0.29
0.09
0.07
0.41
0.56
2.02
0.41
-
C19
1423
-
-
3.60
23.88
11.89
6.56
1436
1438
1443
1447
1455
1461
1471
1476
1480
0.33
1.11
7.32
2.52
0.99
5.12
4.70
0.93
0.58
0.31
1.05
6.69
2.28
0.71
12.79
2.39
0.62
-
2.35
1.00
-
0.34
0.96
6.27
1.91
0.15
5.58
3.22
0.45
-
0.23
0.76
4.83
2.84
0.19
2.87
0.90
3.56
3.31
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C20
C21
C22
C23
C24
C25
Molecules 2021, 26, 5968
5 of 20
Table 1. Cont.
ecules 2021,No.
26, x FORCompound
PEER REVIEW CD 1
55
Germacrene D
C26
56
trans-β-Ionone
57
β-Cadinene
C27
α-Muurolene
C30C28
58
Ledene
γ-Cadinene
59
Bicyclogermacrene C31C29
60
α-Muurolene C32C30
δ-Cadinene
61
γ-Cadinene
C31
Dihydroactinidiolide
62
δ-Cadinene
C32
Cadina-1,4-diene
C33
63
Dihydroactinidiolide
α-Cadinene
C34
64
Cadina-1,4-diene
C33
α-Calacorene
C35C34
65
α-Cadinene
Spathulenol
66
α-Calacorene C36C35
67
Spathulenol
Viridiflorol
C37C36
68
Viridiflorol
C37
α-Cadinol
69
α-Cadinol
0
1
2
3
4
5
6
7
8
9
Total identified [%]
Total identified [%]
RI 2
S. romana
K
S. romana
B
1484
1489
1494
1502
1497
1517
1498
1502
1527
1517
1532
1527
1536
1532
1541
1536
1547
1541
1580
1547
1580
1595
1595
1658
1658
1.50
0.31
2.19
23.04
0.61
0.58
1.84
0.41
0.20
0.24
0.47
0.58
0.42
0.34
0.06
0.18
1.68
20.48
0.18
0.15
0.41
0.04
1.30
0.36
-
86.18
0.61
0.58
1.84
0.41
0.20
0.24
0.47
0.58
0.42
0.34
86.18
90.29
S. romana
M
S. romana
P
0.37
0.18 8.20
0.15 0.41 0.60
0.04 1.30 0.36 - 10.29
-
0.22
1.24
- - 15.16
- 0.60 - 0.33
- - - 10.290.52
- 0.20
-
88.87
89.60
90.29
88.87
S. montana
J
S. montana
M
23.23
0.98
- 2.27
- 4.19
- 1.78
0.333.33
- 7.57
0.11
- 0.94
- 1.41
0.521.05
0.200.15
- 0.08
-
17.04
1.47
1.78 3.3311.76
7.572.93
0.113.37
0.948.85
0.35
1.411.24
1.051.70
0.151.36
0.080.47
- 0.21
-
89.60
89.28
89.28
86.38
5 of
2.93
3.37
8.85
0.35
1.24
1.70
1.36
0.47
0.21
86.38
CD: Compound designation of the major components (average percentages ≥ 1.0% in at least one of the samples), which
1 CD: Compound designation of the major components (average percentages ≥ 1.0% in at least one of the samples), which were included in
were included
in the principal component analysis. 2 RI: Retention index determined relative to a homologous series of nthe principal component analysis. 2 RI: Retention index determined relative to a homologous series of n-alkanes (C9 –C25 ) on a HP-5MS
alkanes (Ccolumn;
9–C25) 3on
a HP-5MS
column; 3 Tentatively identified.
Tentatively
identified.
1
Figure 1. Average
percentages
of different
classesof
of headspace
headspace volatile
organic
compounds
obtainedobtained
from various
Figure 1. Average
relativerelative
percentages
of different
classes
volatile
organic
compounds
from various
populations
of
S.
romana
and
S.
montana
using
DVB/CAR/PDMS
fiber.
populations of S. romana and S. montana using DVB/CAR/PDMS fiber.
2.1.2. PDMS/DVB Fiber
2.1.2. PDMS/DVB Fiber
VOCs of the same four populations of Sideritis romana and two populations of S.
VOCs
theextracted
same four
populations
ofalso
Sideritis
romana
and
two
populations
montanaof
were
by HS-SPME,
using
PDMS/DVB
fiber
and
their
composition of S. m
was
analyzed
by
GC-MS.
In
total,
56
VOCs
were
identified,
accounting
for
89.35–97.09%
tana were extracted by HS-SPME, using also PDMS/DVB fiber and their composition w
of theby
total
VOCs content
(Table
2). As were
with DVB/CAR/PDMS
fiber, thefor
VOCs
compoanalyzed
GC-MS.
In total,
56 VOCs
identified, accounting
89.35–97.09%
of
total VOCs content (Table 2). As with DVB/CAR/PDMS fiber, the VOCs compositions
investigated populations of both species were characterized by sesquiterpene hydroc
bons, followed by monoterpene hydrocarbons, except for that of S. romana M, in wh
monoterpene hydrocarbons and oxygenated sesquiterpenes were more abundant th
Molecules 2021, 26, 5968
6 of 20
sitions of investigated populations of both species were characterized by sesquiterpene
hydrocarbons, followed by monoterpene hydrocarbons, except for that of S. romana M, in
which monoterpene hydrocarbons and oxygenated sesquiterpenes were more abundant
than sesquiterpene hydrocarbons. Moreover, other compounds were more abundant in
this population than in other investigated samples (Figure 2). By applying PDMS/DVB
fiber, more sesquiterpene hydrocarbons, and less oxygenated monoterpenes and other
compounds were extracted than with the application of DVB/CAR/PDMS fiber. The
main individual compounds that were identified for S. romana were bicyclogermacrene
(10.21–57.50%), β-pinene (6.78–13.26%), isocaryophyllene (5.17–7.10%) (except S. romana
M), trans-β-farnesene (3.55–7.71%), germacrene D (1.22–12.18%), γ-terpinene (0.11-8.96%),
limonene (1.97–3.86%) and α-pinene (2.09–3.91%). For S. romana M, the main individual
compounds were viridiflorol (24.19%), β-pinene (13.26%), bicyclogermacrene (10.21%),
γ-terpinene (8.96%) and trans-caryophyllene (6.35%). In S. montana, the main individual
compounds were germacrene D (51.08–53.63%), bicyclogermacrene (9.54–18.03%), transcaryophyllene (6.65–15.49%), limonene (2.91–3.74%) and trans-β-farnesene (2.17–4.02%)
(Table 2).
Table 2. Volatile organic compounds (VOCs) composition (%) of S. romana and S. montana obtained by HS-SPME/GC-MS
with PDMS/DVB fiber.
No.
Compound
1
2
3
4
5
6
7
8
9
10
Pentanal
Hexanal
(E)-Hex-2-enal
α-Thujene
α-Pinene
Camphene
Benzaldehyde
Sabinene
β-Pinene
β-Myrcene
(E,E)-Hepta-2,4dienal
α-Phellandrene
α-Terpinene
p-Cymene
Limonene
Benzyl alcohol
(Z)-β-ocymene
Phenylacetaldehyde
(E)-β-ocymene
γ-Terpinene
Octan-1-ol
α-Terpinolene
Linalool
Nonanal
Benzeneethanol
trans-Pinocarveol 3
Pinocarvone
4-Terpineol
α-Terpineol
Myrtenal
Decanal
Verbenone
2-Phenoxyethanol
Bicycloelemene
α-Cubebene
α-Copaene
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
CD 1
C1′
C2′
C3′
C4′
C5′
C6′
C7′
C8′
C9′
C10′
RI 2
S. romana
K
S. romana
B
S. romana
M
S. romana
P
S. montana
J
S. montana
M
<900
<900
<900
936
944
960
969
981
985
995
0.02
0.02
0.02
0.55
2.09
0.05
0.06
0.56
6.78
0.55
0.03
0.03
0.41
2.31
0.04
0.08
0.35
8.01
0.40
0.12
0.10
0.79
3.91
0.10
0.40
0.46
13.26
0.99
0.03
0.10
0.06
0.58
2.68
0.06
0.15
0.43
10.35
0.80
0.01
0.03
0.07
1.69
0.02
0.04
0.12
1.80
0.28
0.02
0.05
0.04
1.14
0.10
0.10
1.46
0.20
1001
-
0.05
0.12
0.07
0.02
0.03
1011
1023
1032
1036
1040
1043
1051
1054
1066
1075
1093
1103
1107
1117
1145
1169
1182
1195
1199
1208
1212
1223
1342
1353
1375
0.15
0.53
0.81
3.86
0.63
0.03
0.03
0.02
2.53
1.17
0.11
0.03
0.02
0.10
0.06
0.22
0.15
0.04
0.01
2.18
0.07
0.83
0.16
1.97
0.96
0.11
1.33
0.07
0.86
0.05
0.04
0.03
0.58
0.07
2.40
-
0.27
1.15
3.10
3.31
2.55
0.11
8.96
2.46
0.19
0.25
0.35
0.26
0.35
0.41
0.70
0.19
0.10
0.43
-
0.22
1.01
1.57
2.27
1.12
4.49
2.24
0.14
0.22
0.15
0.11
0.11
1.73
-
0.02
3.74
0.16
0.12
0.01
0.02
0.34
0.04
1.33
2.91
0.55
0.02
0.16
0.68
0.05
1.55
Molecules 2021, 26, 5968
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Table 2. Cont.
CD 1
RI 2
S. romana
K
S. romana
B
S. romana
M
S. romana
P
S. montana
J
S. montana
M
α-Gurjunene
trans38
C11′
Caryophyllene
39
Aromadendrene
Alloaromadendrene
40
41
Selina-5,11-diene 3
42
γ-Muurolene
43
trans-β-Farnesene
C12′
44
Isocaryophyllene
C13′
45
α-Amorphene
46
Germacrene D
C14′
47
trans-β-Ionone
48
β-Cadinene
49
Bicyclogermacrene
C15′
lecules 2021,50
26, x FOR
PEER REVIEW
α-Muurolene
51
γ-Cadinene
52
δ-Cadinene
C16′
53
Dihydroactinidiolide
54
Cadina-1,4-diene
5
Spathulenol
55
Spathulenol
6
Viridiflorol
C17′
56
Viridiflorol
C17′
1412
-
-
0.79
-
-
-
1423
0.54
0.91
6.35
2.30
15.49
6.65
1438
1443
1447
1455
1461
1471
1480
1484
1489
1494
1498
1502
1517
1527
1532
1536
1580
1580
1595
1595
0.25
4.88
7.10
12.18
47.32
0.10
0.17
-
0.26
7.71
6.85
2.16
0.27
57.50
0.26
-
3.55
1.77
0.39
10.21
0.42
24.19
0.25
4.90
5.17
1.22
0.16
48.08
0.22
24.19
-
0.06
0.09
4.02
0.19
53.63
0.01
9.54
0.07
0.25
0.91
0.12
0.34
-
0.14
0.32
2.17
51.08
0.01
18.03
0.32
1.32
0.20
0.340.05
-
95.99
97.09
No.
Compound
37
Total identified [%]
Total identified [%]
95.99
97.09
93.06
93.06
92.99
92.99
94.58
94.58
89.35
7 of
89.35
CD: Compound
designation of the major components (average percentages ≥ 1.0% in at least one of the samples), which
1 CD: Compound designation of the major components (average percentages ≥ 1.0% in at least one of the samples), which were included in
2 RI: Retention index determined relative to a homologous series of nwere included
in thecomponent
principal
component
analysis.
2 RI: Retention
the principal
analysis.
index determined
relative to a homologous series of n-alkanes (C9 –C25 ) on a HP-5MS
3
3
Tentatively
identified.
alkanes (Ccolumn;
9–C25) on
a HP-5MS
column; Tentatively identified.
1
Figure 2. Average
percentages
of different
classesof
of headspace
headspace volatile
organic
compounds
obtainedobtained
from various
Figure 2. Average
relativerelative
percentages
of different
classes
volatile
organic
compounds
from various
populations
of S. romana
S. montana
using
PDMS/DVB fiber.
fiber.
populations
of S. romana
and S.and
montana
using
PDMS/DVB
2.2. Principal Component Analysis
In order to analyze the differences between VOCs compositions of investigated
romana and S. montana populations, principal component analysis of the major identif
Molecules 2021, 26, 5968
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2.2. Principal Component Analysis
In order to analyze the differences between VOCs compositions of investigated S.
romana and S. montana populations, principal component analysis of the major identified
components of both taxa was performed, including only those compounds showing at
least 1.0% of the total VOCs content in at least one of the samples (38 compounds in total),
i.e., 37 compounds identified using DVB/CAR/PDMS fiber and 17 compounds identified
using PDMS/DVB fiber (Table 3).
Table 3. Composition (%) of major identified VOCs of S. romana and S. montana obtained by HS-SPME/GC-MS with
DVB/CAR/PDMS and PDMS/DVB fiber.
No.
Compound
CD 1 (A 2 /B 3 )
S. romana
K
(A 2 /B 3 )
S. romana
B
(A 2 /B 3 )
S. romana
M
(A 2 /B 3 )
S. romana
P
(A 2 /B 3 )
S. montana
J
(A 2 /B 3 )
S. montana
M
(A 2 /B 3 )
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Acetic acid
α-Thujene
α-Pinene
Benzaldehyde
β-Pinene
β-Myrcene
α-Phellandrene
α-Terpinene
p-Cymene
Limonene
Benzyl alcohol
γ-Terpinene
Octan-1-ol
α-Terpineol
Myrtenal
Bicycloelemene
α-Copaene
α-Gurjunene
Aristolene
transCaryophyllene
Aromadendrene
Alloaromadendrene
Selina-5,11-diene 4
trans-β-Farnesene
Isocaryophyllene
α-Amorphene
Germacrene D
β-Cadinene
Ledene
Bicyclogermacrene
α-Muurolene
γ-Cadinene
δ-Cadinene
Cadina-1,4-diene
α-Cadinene
α-Calacorene
Spathulenol
Viridiflorol
C1/C2/C3/C1′
C4/C5/C2′
C6/C7/C8/C3′
C9/C4′
C10/C5′
C11/C6′
C12/C7′
C13/C8′
C14/C15/-/C9′
C16/C10′
C17/C18/-
-/0.47/0.55
1.32/2.09
0.44/0.06
3.69/6.78
0.80/0.55
0.32/0.15
0.62/0.53
0.99/0.81
6.34/3.86
2.96/0.63
1.75/2.53
1.37/1.17
0.50/0.22
0.39/0.15
0.75/2.18
0.18/0.07
1.17/1.08/-
0.85/1.03/0.41
0.94/2.31
0.32/0.08
2.61/8.01
0.84/0.40
3.37/0.83
0.61/1.81/0.16
7.58/1.97
3.82/0.96
0.98/0.11
2.22/1.33
3.85/0.58
0.54/0.07
0.53/2.40
-/0.95/0.91/-
3.11/1.08/0.79
2.51/3.91
2.58/0.40
6.67/13.26
1.27/0.99
2.54/0.27
1.32/1.15
5.49/3.10
7.10/3.31
13.28/2.55
3.67/8.96
3.55/2.46
1.25/0.41
1.03/0.70
-/0.43
-/0.61/0.79
-/-
1.33/0.21/0.58
2.19/2.68
0.71/0.15
8.01/10.35
0.88/0.80
0.20/0.22
0.38/1.01
1.32/1.57
1.68/2.27
3.84/1.12
1.40/4.49
2.50/2.24
0.02/0.47/0.11
0.40/1.73
-/0.85/-/-
0.32/0.16/0.07
3.42/1.69
0.37/0.04
2.81/1.80
0.91/0.28
0.10/0.02
0.07/0.04/8.14/3.74
0.84/0.16
0.08/0.35/0.12
0.04/-/0.02
0.22/0.34
1.67/1.33
0.12/-/-
0.55/0.05/0.04
1.23/1.14
0.42/0.10
1.52/1.46
0.64/0.20
0.09/0.07/0.05/6.31/2.91
2.14/0.55
0.08/0.29/0.16
-/-/0.41/0.68
2.02/1.55
0.41/-/-
C19/C11′
-/0.54
-/0.91
3.60/6.35
23.88/2.30
11.89/15.49
6.56/6.65
C20/C21/C22/C23/C12′
C24/C13′
C25/C26/C14′
C27/C28-/
C29/C15′
C30/C31/C32/C16′
C33/C34/C35/C36/C37/C17′
1.11/0.25
7.32/2.52/5.12/4.88
4.70/7.10
0.58/1.50/12.18
2.19/-/23.04/47.32
0.61/0.58/1.84/0.10
0.20/0.24/0.47/0.58/0.42/-
1.05/6.69/2.28/0.26
12.79/7.71
2.39/6.85
-/0.06/2.16
1.68/-/20.48/57.50
0.18/-/0.15/-/-/0.04/1.30/0.36/-
-/2.35/-/1.00/3.55
-/-/-/1.77
-/8.20/-/10.21
-/-/-/-/-/-/-/10.29/24.19
0.96/6.27/0.25
1.91/5.58/4.90
3.22/5.17
-/-/1.22
1.24/-/15.16/48.08
-/-/-/-/-/-/0.52/0.20/-
0.23/0.76/0.06
-/4.83/4.02
-/2.84/0.19
23.23/53.63
0.98/0.01
2.27/4.19/9.54
1.78/0.07
3.33/0.25
7.57/0.91
0.94/1.41/1.05/0.15/0.34
0.08/-
2.87/0.90/0.14
-/3.56/2.17
-/3.31/17.04/51.08
1.47/0.01
-/11.76/18.03
2.93/3.37/0.32
8.85/1.32
1.24/0.05
1.70/1.36/0.47/0.21/-
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
1
CD: Compound designation of the major components (average percentages ≥ 1.0% in at least one of the samples), which were included in
the principal component analysis; 2 A: Compound extracted using DVB/CAR/PDMS fiber; 3 B: Compound extracted using PDMS/DVB
fiber; 4 Tentatively identified.
Molecules 2021, 26, 5968
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2.2.1. DVB/CAR/PDMS Fiber
The biplot constructed by the first two principal components that are showing the
distribution of investigated S. romana and S. montana populations and VOCs identified with
DVB/CAR/PDMS fiber is presented in Figure 3. Principal component 1 (PC1) accounted
for 49.37% and principal component 2 (PC2) for 30.62% of total variance in the data. Clear
separation between S. romana and S. montana was obtained. For all populations of S.
romana, except for S. romana M, distinctive components for discrimination observed by
using DVB/CAR/PDMS fiber were bicyclogermacrene (C29), alloaromadendrene (C21),
trans-β-farnesene (C23), isocaryophyllene (C24), selina-5,11-diene (C22), α-gurjunene (C17)
and spathulenol (C36), while S. romana M, was characterized by benzyl alcohol (C11),
viridiflorol (C37), ledene (C28), p-cymene (C9), acetic acid (C1), benzaldehyde (C4) and
β-myrcene (C6). Distinctive components for discrimination of S. montana populations were
germacrene D (C26), δ-cadinene (C32), γ-cadinene (C31), α-amorphene (C25), α-muurolene
(C30), α-copaene (C16), α-cadinene (C34), cadina-1,4-diene (C33) and α-calacorene (C35).
Figure 3. Biplot obtained by principal component analysis of VOCs composition of investigated populations of S. romana
and S. montana, based on major components with average percentages ≥ 1% in at least one of the samples, detected with
DVB/CAR/PDMS fiber.
Molecules 2021, 26, 5968
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2.2.2. PDMS/DVB Fiber
The biplot constructed by the first two principal components that are showing the
distribution of investigated S. romana and S. montana populations and VOCs identified
with PDMS/DVB fiber is presented in Figure 4. Principal component 1 (PC1) accounted
for 55.88% and principal component 2 (PC2) for 33.21% of total variance in the data.
Clear separation between S. romana and S. montana was obtained. Distinctive components
observed by using PDMS/DVB fiber for all S. romana populations, except for S. romana
M, were bicyclogermacrene (C15′ ), isocaryophyllene (C13′ ), trans-β-farnesene (C12′ ) and
bicycloelemene (C9′ ). S. romana M population was characterized by viridiflorol (C17′ ),
γ-terpinene (C7′ ), α-pinene (C1′ ), p-cymene (C4′ ), benzyl alcohol (C6′ ) and α-terpinene
Molecules 2021, 26, x FOR PEER REVIEW (C3′ ). Distinctive components for discrimination of S. montana were germacrene D (C14′ ), 10 of 19
α-copaene (C10′ ) and δ-cadinene (C16′ ).
Biplot obtained by principal component analysis of VOCs composition of investigated populations of S. romana
Figure 4.Figure
Biplot4. obtained
by principal component analysis of VOCs composition of investigated populations of S. romana
and S. montana, based on major components with average percentages ≥ 1% in at least one of the samples, detected with
and S. montana, based on major components with average percentages ≥ 1% in at least one of the samples, detected with
PDMS/DVB fiber.
PDMS/DVB fiber.
3. Discussion
Depending on the polarity of VOCs of an analyte, several types of fibers may be used
for extracting different groups of compounds such as PDMS (a non-polar fiber used for
Molecules 2021, 26, 5968
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3. Discussion
Depending on the polarity of VOCs of an analyte, several types of fibers may be
used for extracting different groups of compounds such as PDMS (a non-polar fiber
used for volatile compounds), PA (a polar fiber used for polar semi-volatile compounds),
CW/DVB (a polar fiber used for alcohols and volatiles), PDMS/DVB (a bipolar fiber used
for volatile compounds of medium polarity, amines and nitroaromatics), CAR/PDMS (a
bipolar fiber used for low molecular weight volatile compounds) and DVB/CAR/PDMS
(a bipolar fiber used for polar and non-polar volatile compounds) [34,36]. In this study,
DVB/CAR/PDMS and PDMS/DVB fiber, which were previously shown to be most suitable for untargeted HS-SPME analysis of volatiles [35], were used for the analysis of VOCs
from aerial parts of S. romana and S. montana from Croatia. In our study, the number of
extracted VOCs was higher using DVB/CAR/PDMS fiber (69 compounds) than it was by
using PDMS/DVB fiber (56 compounds), which is in accordance with the work of Wang
et al. [37], in which DVB/CAR/PDMS fiber showed better efficiency to extract volatile
compounds (50 compounds) from the samples of Aquilegia japonica Nakai and H.Hara,
compared to CAR/PDMS (47 compounds) and PDMS/DVB fibers (45 compounds), as well
as with the work of Sukkaew et al. [38], where more volatile components were extracted
using DVB/CAR/PDMS fiber (51 compounds) than with PDMS/DVB (38 compounds),
PDMS (38 compounds) and CAR/PDMS (37 compounds) fibers in Murraya koenigii (L.)
Sprengel fresh leaves. In our study, the dominant chemical classes of volatile compounds
in all samples of the two investigated Sideritis species extracted using DVB/CAR/PDMS
and PDMS/DVB fibers were sesquiterpene hydrocarbons followed by monoterpene hydrocarbons, except for S. romana M in whose extract monoterpene hydrocarbons were
more abundantly present. The obtained results for S. montana are in accordance with the
results reported by Venditti et al. [23] for EO of S. montana subsp. montana from central
Italy obtained by hydrodistillation, where sesquiterpene hydrocarbons led by germacrene
D and bicyclogermacrene were observed as the most abundant EO components. According
to the latter, oil-poor species from Lamioideae subfamily produce EOs rich in sesquiterpene hydrocarbons. Furthermore, our results are in accordance with the classification of
Sideritis species from Turkey given by Kirimer et al. [18], based on the main components of
hydrodistilled EOs, where S. montana ssp. montana was classified into the sesquiterpene
hydrocarbons-rich group, and S. romana ssp. romana into the oxygenated monoterpenes-rich
group. Considering the relative percentages of extracted chemical classes, in comparison
to PDMS/DVB fiber, DVB/CAR/PDMS fiber extracted more oxygenated monoterpenes
and other compounds (mostly non-terpenes), which were more abundantly present in
investigated S. romana populations. Conversely, in accordance with previously reported
findings [36], PDMS/DVB fiber was observed to be more efficient in extracting sesquiterpene hydrocarbons, which were relatively higher in investigated S. montana populations
when comparing to the results obtained for the S. romana populations included in this study.
In fact, for both species, the most abundant VOCs, namely the sesquiterpene hydrocarbons
germacrene D (S. montana) and bicyclogermacrene (S. romana, except for S. romana M) were
extracted more efficiently by PDMS/DVB fiber. The same was observed for viridiflorol,
an oxygenated sesquiterpene that was found as the major characteristic compound of the
chemically distinct population of S. romana from Morinje Bay (S. romana M).
Molecules 2021, 26, 5968
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The dominant compounds of S. romana (except S. romana M) extracted with DVB/CAR/
PDMS fiber were bicyclogermacrene, trans-caryophyllene, trans-β-farnesene, limonene
and alloaromadendrene, while bicyclogermacrene, β-pinene, isocaryophyllene, transβ-farnesene, germacrene D and γ-terpinene were dominant after the extraction with
PDMS/DVB fiber. A different composition of EO was reported for S. romana from Italy,
where carvacrol, limonene and 1,8-cineole were reported as the dominant compounds
isolated by hydrodistillation [19], while neither carvacrol and 1,8-cineole nor thymol, oct-1en-3-ol and borneol, reported as the dominant compounds isolated by hydrodistillation
from S. romana subsp. romana from Turkey [18], were detected in our samples of S. romana
from Croatia. For S. romana M, the dominant compounds extracted with DVB/CAR/PDMS
were benzyl alcohol, viridiflorol, ledene and limonene, while with PDMS/DVB these
were viridiflorol, β-pinene, bicyclogermacrene and γ-terpinene. These results are not in
accordance with the previously mentioned studies of S. romana from Italy and Turkey.
For other subspecies of S. romana, such as S. romana subsp. purpurea from Greece, bicyclogermacrene, β-caryophyllene (=trans-caryophyllene or isocaryophyllene), γ-muurolene,
β-pinene, (E)-β-farnesene (=trans-β-farnesene) and spathulenol were found as the major
components obtained by hydrodistillation [21], while for the same subspecies from Montenegro, the major EOs constituents obtained by steam distillation were γ-elemene and
spathulenol [27]. Moreover, the most abundant EO components obtained by hydrodistillation from the same subspecies, which was also collected in Montenegro, included
bicyclogermacrene, germacrene D, (E)-caryophyllene and spathulenol [20]. According
to the PCA analysis, even though it was present with more than 1% only in one of the
analyzed samples, spathulenol appeared to be one of the compounds distinctive for S.
romana. However, it was not found in S. romana M, which was observed to contain much
lower amounts of bicyclogermacrene, which were detected only using PDMS/DVB fiber.
However, spathulenol may be an artifact, having in mind that bicyclogermacrene is easily
converted to spathulenol at room temperature [39]. The compound may also be formed
during the process of hydrodistillation, as seen in the comparison of EO composition
and VOCs composition of S. scardica samples prepared by other techniques of isolation
such as solvent extraction and supercritical carbon dioxide extraction [40]. On the other
hand, distinctive VOCs of S. romana M such as viridiflorol (detected in higher amount
using PDMS/DVB fiber) and ledene (detected only using DVB/CAR/PDMS fiber) may
be the result of bicyclogermacrene hydration and/or rearrangement [41,42]. According to
Carvalho et al. [43], who studied the volatile fractions of in natura, fresh, and dried Casearia
sylvestris var. sylvestris Sw. and var. lingua (Cambess.) Eichler leaves, viridiflorol is an
artifact most likely formed from bicyclogermacrene, whose content increases during the
drying process. As it can be seen from Table 4, the distinct sample of S. romana from Morinje
Bay (S. romana M) was collected prior to other samples of the same species and, therefore,
may have been more susceptible to transformations during processing and storage of plant
material, having in mind that all collected samples were analyzed simultaneously. The
sample from Morinje Bay also contained more other compounds (non-terpenes), which
were mostly oxygenated compounds (alcohols, aldehydes and a carboxylic acid), indicating
its possible oxidative degradation. Other compounds that were present and/or were more
abundant in S. romana populations other than S. romana M, such as alloaromadendrene and
aromadendrene, may also have been formed by isomerization from bicyclogermacrene [44]
and could have produced spathulenol by further oxidation [43].
Molecules 2021, 26, 5968
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Table 4. Sample codes, voucher numbers, harvesting locations, geographic coordinates and climatic affiliations according to
Köppen climate classification for investigated Sideritis species.
Species
S. romana
S.
montana
Sample
Code
Voucher
No.
S. romana K
18 021
S. romana B
18 023
S. romana M
18 020
S. romana P
18 022
S. montana J
18 010
S. montana M
18 011
Location
Istria,
Kamenjak
Dalmatia,
Blato
Dalmatia,
Morinje Bay
Dalmatia,
Brač,
Pražnica
Dalmatia,
Ježević
Dalmatia,
Mosor,
Gornje Sitno
Date of
Collection
Latitude
Longitude
Köppen Climate
Classification 1
13 June 2020
44◦ 47′ 46.15” N
13◦ 54′ 25.96” E
Cfa 2
21 June 2020
43◦ 10′ 12.71” N
17◦ 11′ 45.75” E
Csa 3
7 June 2020
43◦ 40′ 44.79” N
15◦ 57′ 41.25” E
Csa 3
20 June 2020
43◦ 19′ 1.3” N
16◦ 40′ 24.45” E
Csb 4
6 June 2020
43◦ 55′ 1.51” N
16◦ 28′ 8.41” E
Cfb 5
22 June 2020
43◦ 31′ 13.56” N
16◦ 36′ 10.44” E
Cfa 2
1
Data obtained from Šegota and Filipčić [45]; 2 Cfa: temperate humid climate with hot summer; 3 Csa: Mediterranean climate with hot
summer; 4 Csb: Mediterranean climate with warm summer; 5 Cfb: temperate humid climate with warm summer.
Comparable to our results, variations in bicyclogermacrene content were observed
in aroma compounds isolated by hydrodistillation of dried aerial parts from different
populations of S. scardica and S. raeseri from Macedonia [29]. Moreover, it was reported by
Kirimer et al. [46] in their extensive study conducted on 50 Sideritis taxa from the section
Empedoclia that viridiflorol was one of the major components isolated by hydrodistillation
from S. perfoliata L. from Turkey, while the same compound was not observed for this
species in a subsequent study done by the same authors conducted on only two species [47].
Additionally, viridiflorol was found as one of the major constituents of EO isolated by
hydrodistillation from S. montana subsp. montana from Turkey together with germacrene
D, bicyclogermacrene and (E)-β-farnesene [18]. In the present study, the predominant
compounds for S. montana extracted with DVB/CAR/PDMS fiber were germacrene D, transcaryophyllene, δ-cadinene, bicyclogermacrene, limonene and trans-β-farnesene, while with
PDMS/DVB fiber germacrene D was followed by bicyclogermacrene, trans-caryophyllene,
limonene and trans-β-farnesene. In investigated samples of S. montana, as well as in the
samples of S. romana other than S. romana M, viridiflorol was found only in trace amounts
(<1%), while ledene was observed only in S. montana from Ježević (S. montana J), the latter
being the previously collected and thus older of the two investigated samples of S. montana
(stored for a slightly longer period before GC-MS analysis). Considering that a significantly
lower amount of bicyclogermacrene was detected in the same sample compared to S.
montana from Mosor (S. montana M), ledene may have been formed during the drying
and storage period from the aforementioned bicyclogermacrene. Our results considering
the major VOCs of investigated populations of S. montana are in accordance with the
results of previous studies from Bulgaria [22], Turkey [18], Serbia [25] and Italy [23], in
which germacrene D predominated in the chemical composition of EOs isolated from
aerial parts by hydrodistillation, usually being followed by bicyclogermacrene. Different
major compounds were reported for S. montana from Iran, in which geraniol particularly
predominated in the EO obtained by hydrodistillation from the flowering spikes of the
plant [26], while it was not detected in our samples of S. montana aerial parts, as well
as for S. montana subsp. montana from Turkey, in which β-caryophyllene, α-pinene and
β-pinene were found to be the major compounds of the hydrodistilled EO obtained from
aerial parts of the plant [24]. The present study also indicated that S. montana, unlike S.
romana, is characterized by several sesquiterpene hydrocarbons having a cadalane skeleton
(δ-cadinene, γ-cadinene, α-amorphene, α-muurolene, α-cadinene, and cadina-1,4-diene).
Molecules 2021, 26, 5968
14 of 20
Clear separation between S. montana and S. romana samples was observed in the PCA with
both fiber types used, with S. romana M showing a distinct VOCs profile.
Observed differences in the chemical composition of investigated Croatian Sideritis
species from previously published data on VOCs composition of aerial parts from samples
of different geographical origins may be explained by different ecological conditions
(Table 4). According to Köppen climate classification [45], the collection areas from which
the populations included in the present study were sampled belong to different climates
including the Mediterranean climate with hot summer (S. romana B, S. romana M), the
Mediterranean climate with warm summer (S. romana from Pražnica (S. romana P)), the
temperate humid climate with hot summer (S. romana K, S. montana M) and the temperate
humid climate with warm summer (S. montana J). This might have party affected their
VOCs production. As it is known, VOCs composition can change depending on the type
of stimulus received from the environment [32]. For example, variation of VOCs content
may have been caused by environmental stress such as drought stress, as it was detected in
the study of different cultivars of Thymus vulgaris L., in which α-phellandrene, o-cymene,
γ-terpinene and β-caryophyllene were recognized as the compounds included in drought
stress adaptation [48]. These compounds were observed as one of the major identified
VOCs in the present study. For example, γ-terpinene was found to be especially dominant
in S. romana M. Additionally, individual VOCs production might have been affected by the
plant species that grew in the vicinity of investigated specimens in each habitat (place of
collection) [49,50]. Although this has not been recorded in the present study, insight into
the diversity of plant species in the harvesting locations can be partially gained through
floristic studies that were conducted in the areas that are overlapping with or are near to
the harvesting locations [51–59].
Besides ecological conditions, the observed differences may also be explained by the
applied methods of extraction, having in mind that none of the previously mentioned
studies used the HS-SPME method for extraction of VOCs from S. romana and S. montana. Instead, as already mentioned above, most authors used hydrodistillation, with the
exception of the study done by Garzolli et al. [27], in which steam distillation was used.
A few comparative analyses of plant volatile compounds isolated by hydrodistillation
and HS-SMPE were published. A study on Myrtus communis L. showed that the applied
microextraction techniques (HS-SPME and HS-SDME) extracted compounds that were
more volatile, such as α-pinene and limonene, in comparison to hydrodistillation, which,
in turn, obtained higher peak areas for low volatile compounds [60]. Moreover, analysis of
volatile compounds from fruits of Seseli libanotis (L.) W.D.J.Koch also showed that higher
contents of low-boiling compounds such as sabinene, β-phellandrene, α-pinene, β-pinene,
β-myrcene, γ-terpinene and α-phellandrene may be extracted by using HS-SPME than
by hydrodistillation, while higher amounts of high-boiling compounds (higher molecular
mass and lower volatility) were observed using hydrodistillation at high temperature [61].
Qualitative and quantitative differences of volatile compounds of Melissa officinalis L. were
observed after applying hydrodistillation and HS-SPME, which may be attributed to the
formation of artifacts [6]. Furthermore, variations in the percentages and nature of compounds adsorbed on a SPME fiber compared to those found in hydrodistilled EOs were
reported for Petroselinum crispum Mill. [62], while the comparison of the same techniques
on Bupleurum plantagineum Desf. showed differences mainly in minor components [63].
Therefore, despite some differences, the results obtained by HS-SPME considering the
major VOCs may be comparable to the results obtained by hydrodistillation [61–63].
In the studied samples, the most abundant VOCs, depending on the fiber used for
solid-phase microextraction, were bicyclogermacrene (S. romana K, S. romana B and S.
romana P) and/or trans-caryophyllene (S. romana P), benzyl alcohol or viridiflorol (S. romana
M), and germacrene D (S. montana J and S. montana M). These compounds were previously
shown to possess certain biological activities that may be of interest to the pharmaceutical,
food and/or cosmetics industry. For example, bicyclogermacrene displayed cytotoxic activity against a range of cancer cell lines (IC50 = 3.1–21 µg/mL [64] and IC50 = 1.5–4.4 µg/mL).
Molecules 2021, 26, 5968
15 of 20
The same was observed for germacrene D (IC50 = 2.7–8.0 µg/mL) [65]. Additionally,
germacrene D and trans-caryophyllene were recognized as the major EO constituents of
selected species from the genera Siparuna Aublet and Piper L. that possess antiradical
activity [66]. According to Dahham et al. [67], β-caryophyllene possesses antibacterial
activity against S. aureus (MIC = 3 ± 1.0 µM) as well as anti-fungal (MIC = 4–7 µM), antioxidant (IC50 = 1.25–3.23 µM), and anti-proliferative activity against colorectal cancer cells
(IC50 = 19 µM). Benzyl alcohol is frequently used as a bacteriostatic agent in liquid pharmaceutical products [68] as well as a preservative in cosmetic products [69]. On the other
hand, antiradical (IC50 = 57.55–74.7 µg/mL), anti-mycobacterial (MIC = 190.0 µg/mL) and
anti-inflammatory activity (60% reduction of carrageenan-induced mice paw edema after
3–30 mg/kg oral administration) were reported for viridiflorol [70]. Moreover, viridiflorol
was recently observed to induce intracellular Ca2+ mobilization in human neutrophils and
C20 microglial cells [71].
Related species of the genus Sideritis, namely S. scardica [22,29,72], S. clandestina (Bory
and Chaub.) Hayek [21], S. raeseri [72–74], and S. syriaca L. [22], whose aerial parts have
been traditionally used for the treatment of inflammation, gastrointestinal disorders and
cough associated with cold and whose usage has been approved by the European Medicines
Agency (EMA) Committee on Herbal Medicinal Products (HMPC) [75], were observed
to possess, as one of their major volatile constituents, the same VOCs that were found in
S. romana and S. montana in the present study, thus, indicating a promising potential for
future investigations of these species.
4. Materials and Methods
4.1. Plant Material
Aerial parts of S. romana (four samples, consisting of 5–15 cm long shoots) and S. montana (two samples, consisting of 7–26 cm long shoots) were collected during the flowering
period in June 2020 from natural populations on several locations in Croatia (Figure 5). In
the field, the plant material was stored in paper bags and later spread out into one layer to
dry out, in a place with room temperature. The mass of dried samples ranged between
2 and 22 g for S. romana and between 3 and 11 g for S. montana. Taxonomic identification
was performed by T. M. Voucher specimens have been deposited within the Herbarium
of the Department of Pharmaceutical Botany, University of Zagreb Faculty of Pharmacy
and Biochemistry, Croatia. Sample codes, voucher numbers, harvesting locations and
geographic coordinates are given in Table 4.
4.2. SPME Fibers and Extraction Procedure
HS-SPME was achieved with a manual SPME holder by using two fibers, (divinylbenzene/carboxene/polydimethylsiloxane (DVB/CAR/PDMS) and polydimethylsiloxane/divinylbenzene (PDMS/DVB)), that were conditioned according to Supelco Co. instructions before extraction. Cut samples (1 g) were placed separately in glass vials (5 mL)
and sealed hermetically using PTFE/silicone septa. The vials were maintained in a water
bath (60 ◦ C) during equilibration (15 min) and extraction by HS-SPME (45 min). After
extraction, the SPME fiber was withdrawn and inserted into the GC-MS injector (250 ◦ C)
for thermal desorption (6 min). The treatment was similar as previously reported [76].
HS-SPME was performed in duplicate and average values are presented in Tables 1–3.
Molecules 2021, 26, 5968
between 2 and 22 g for S. romana and between 3 and 11 g for S. montana. Taxonomic identification was performed by T. M. Voucher specimens have been deposited within the
Herbarium of the Department of Pharmaceutical Botany, University of Zagreb16Faculty
of
of 20
Pharmacy and Biochemistry, Croatia. Sample codes, voucher numbers, harvesting locations and geographic coordinates are given in Table 4.
Figure5.5.Harvesting
Harvesting
locations
investigated
Sideritis
species.
Figure
locations
forfor
investigated
Sideritis
species.
4.3.
4.2.GC-MS
SPME Analysis
Fibers and Extraction Procedure
GC-MS
analyses
performed
a gas chromatograph
model
7820A
HS-SPME
was were
achieved
with aon
manual
SPME holder by
using
two (Agilent
fibers, (diviTechnologies,
Palo
Alto,
CA,
USA)
containing
a
HP-5MS
capillary
column
(5% phenylnylbenzene/carboxene/polydimethylsiloxane (DVB/CAR/PDMS) and polydimethylsiloxmethylpolysiloxane,
J and W; that
30 mwere
× 0.25
mm i.d., coating
thickness
0.25 µm)
ane/divinylbenzeneAgilent
(PDMS/DVB)),
conditioned
according
to Supelco
Co. inand a mass selective detector (MSD) model 5977E (Agilent Technologies, Palo Alto, CA,
structions before extraction. Cut samples (1 g) were placed separately in glass vials (5 mL)
USA). The GC conditions were described previously [76,77]. The carrier gas was helium
and sealed hermetically using PTFE/silicone septa. The vials were maintained in a water
(He 1.0 mL/min). The oven temperature was set at 70 ◦ C for 2 min, then it was increased
bath70
(60
during
(15 min)
by HS-SPME
min).
◦ C°C)
◦ C atequilibration
from
to 200
a rate of 3 ◦ C/min,
andand
heldextraction
at 200 ◦ C for
15 min. The(45
MSD
(EI After
extraction,
the
SPME
fiber
was
withdrawn
and
inserted
into
the
GC-MS
injector
(250 °C)
mode) was used at 70 eV, and 30–300 amu mass range was applied.
for thermal
desorption
(6 min). The
treatment
as indices
previously
[76]. HSThe compounds
identification
was
based onwas
thesimilar
retention
(RIs)reported
determined
SPME
was
performed
in
duplicate
and
average
values
are
presented
in
Table
1,
Table 2
relative to retention times of n-alkanes (C9 -C25 ) and their comparison with literature data
and
Table
3.
(National Institute of Standards and Technology) as well as by their mass spectra compared
with the spectra from Wiley 9 (Wiley, New York, NY, USA) and NIST 17 (Gaithersburg,
4.3. USA)
GC-MS
Analysis
MD,
mass
spectral libraries. The percentage composition was calculated using the
normalization
method
(without
correction factors).
Thechromatograph
average component
percentages
in
GC-MS analyses
were performed
on a gas
model
7820A (Agilent
Table
1–3
were
calculated
from
duplicate
GC-MS
analyses
[76,77].
Technologies, Palo Alto, CA, USA) containing a HP-5MS capillary column (5% phenyl-
methylpolysiloxane,
4.4.
Principal ComponentAgilent
AnalysisJ and W; 30 m × 0.25 mm i.d., coating thickness 0.25 μm) and
a mass selective detector (MSD) model 5977E (Agilent Technologies, Palo Alto, CA, USA).
Principal component analysis (PCA) was conducted on the volatile constituents havThe GC conditions were described previously [76,77]. The carrier gas was helium (He 1.0
ing an average relative percentage ≥ 1.0% in at least one of the samples (in total, six
mL/min). The
temperature
was set at 70 fiber
°C for
2 min,
then it wasofincreased
from 70
observation
of 37oven
variables
for DVB/CAR/PDMS
and
six observations
17 variables
°C
to
200
°C
at
a
rate
of
3
°C/min,
and
held
at
200
°C
for
15
min.
The
MSD
(EI
mode)
for PDMS/DVB fiber), in order to examine the interrelationships among the investigated was
used at 70 eV,
30–300
amu
mass range
was
applied.(two populations), in RStudio
populations
of S.and
romana
(four
populations)
and
S. montana
version 1.4.1717 [78] using the function prcomp in R version 4.1.1. [79]. Scaling was set to
“TRUE” to perform the analysis on normalized data. Plotting was performed using the
function autoplot from the package ggfortify [80,81].
Molecules 2021, 26, 5968
17 of 20
5. Conclusions
Headspace volatile organic compounds (VOCs) profile of aerial parts of altogether
six native populations of Sideritis romana and S. montana from Croatia were determined
by HS-SPME/GC-MS, using DVB/CAR/PDMS and PDMS/DVB fibers for compound
extraction, which resulted in identification of 69 and 56 compounds, respectively. The
most abundant VOCs in both species were those belonging to the class of sesquiterpene
hydrocarbons, which were extracted more efficiently using PDMS/DVB fiber. The performed PCA analyses highlighted the major volatile constituents for each population and
revealed clear separation between the investigated species using both fiber types. The
most abundant VOCs found in the analyzed samples of S. romana were bicyclogermacrene
and/or trans-caryophyllene or viridiflorol and benzyl alcohol, while germacrene D was
the most abundant VOC found in the analyzed samples of S. montana, all of which were
previously reported to possess certain biological activities that are potentially interesting
for the pharmaceutical, food and/or cosmetics industry. The observed differences in the
presence and amount of detected volatile compounds among the researched populations
of the same species may be a result of different environmental and ecological conditions
existing on the collection sites, while specific differences may also be attributed to changes
that might have occurred during drying and storage of sampled plant material. The obtained results, according to which S. romana and S. montana show a promising potential
for future utilization, suggest that the origin of plant material and/or growing as well as
processing conditions should be considered as possible factors affecting VOCs production
if these species were to be exploited.
Author Contributions: Conceptualization, T.M. and M.F.; collection of plant material, T.M.; HS-SPME
and GC-MS analysis, Z.M. and I.J.; PCA analysis, M.F; data analysis, T.M. and M.F.; supervision,
Ž.M. and I.J.; visualization, M.F.; writing—original draft, T.M. and M.F.; writing—review and editing,
T.M., M.F., I.J. and Ž.M.; funding acquisition, M.F. All authors have read and agreed to the published
version of the manuscript.
Funding: The APC was funded by the University of Zagreb (Z-209).
Data Availability Statement: The data presented in this study are available in article.
Acknowledgments: The authors would like to thank the University of Zagreb for financial support.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds are available from the authors.
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