# Antibacterial Activity ofDaucus crinitus Essential Oils along the Vegetative Life of the Plant

Authors: Amel Bendiabdellah; Mohammed El Amine Dib; Nawel Meliani; Alain Muselli; Djabou Nassim; Boufeldja Tabti; Jean Costa
Journal: Journal of Chemistry
 (2013)

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## Abstract

The essential oils from the aerial parts ofDaucus crinitus Desf. were analyzed at three developmental stages (early vegetative, early flowering, and full flowering). Oil yield was found to vary depending on the stage of development, and the highest content of oil (0.15% w/w) was obtained at full flowering. The chemical composition of essential oils studied by GC and GC-MS showed a total of 71 compounds: 27 aliphatic compounds, 18 sesquiterpene hydrocarbons, 9 hydrocarbons monoterpene, 5 oxygenated monoterpenes, 5 phenolic compounds, 4 oxygenated sesquiterpenes, 2 oxygenated diterpenes, and 01 diterpene hydrocarbons. Whatever the analyzed stage, phenolic compounds were the most abundant group. Their level significantly increased during ripening and varied from 36.4 to 82.1%. Antimicrobial activities of oils were tested on four different microorganisms. The oils of various phenological stages showed high activity against Candida albicans (30 mm) and Staphylococcus aureus (11–28 mm) bacteria strains which are deemed very dangerous and very difficult to eliminate. Thus, they represent an inexpensive source of natural antibacterial substances that may potentially be used in pathogenic systems.


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## Body

## 1. Introduction

In the last years, interest in medicinal plants as an alternative to synthetic drugs is more and more increasing, particularly against microbial agents because of the growth of antibiotic resistance. Essential oils of various species of edible and medicinal plants, herbs, and spices constitute a wide source of natural biologically active agents [1]. Their components have many applications in ethnomedicine, food, beverages, preservation, cosmetics as well as in the fragrance and pharmaceutical industries [2–4]. For a long time, plants from the Apiaceae family have been used as spices or drugs, particularly due to their essential oils. A dozen important herbal medicinal products from this botanic family are described in some pharmacopoeias, having antiseptic, expectorant, diuretic, carminative, vasodilator, or spasmolytic actions [5]. Variation in chemical composition of essential oils may be due to many factors, such as the genetic factors, phenological stages, the environmental conditions, and the pedoclimatic conditions. Antimicrobial activity of an essential oil is attributed mainly to its major components, although the synergistic or antagonistic effect of one minor compound of the mixture has to be considered [6]. Therefore, antimicrobial and other biological activities may vary, based on the variations in the chemical composition [7, 8]. Daucus crinitus Desf. is characterized by the presence of many subspecies that colonize the sands and cliffs [9]. A survey conducted by herbalists identified that, in folk medicine, a drink made from the roots of D. crinitus is used in decoction to expel the placenta after childbirth, as a tonic and coldness. From a chemical point of view, D. crinitus has been only the subject of two studies on the chemical composition of essential oil. The aerial parts oil were characterized by isochavicol isobutyrate, octyl acetate, α-pinene, and isochavicol 2-methylbutyrate [10, 11]. However, roots oil was mainly composed of aliphatic compounds [10]. In fact, during ontogenesis a number of transformations occur, revealed by morphological changes and variability of physiological processes [12]. The aim of this research is to study the essential oil compositions of aerial parts of D. crinitus during three vegetative stages and its coherence with antibacterial activity in order to find new bioactive natural products.


## 2. Material and Methods

### 2.1. Plant Material

D. crinitus were collected in Chelaida forest area (at about 8 km northeast of Tlemcen, Algeria). Stems/leaves essential oils used for the comparative study were obtained from wild plants collected at the end of March (early vegetative), at mid-May (early flowering), and at the end of July (full flowering).


### 2.2. Essential Oil Extraction

D. crinitusessential oils were isolated by hydrodistillation (400–450 g of dried plant per sample) for 6 h using a Clevenger-type apparatus [13] according to the European Pharmacopoeia.


### 2.3. Gas Chromatography Analysis (GC)

GC analyses were carried out using a Perkin-Elmer (Waltham, MA, USA) Autosystem XL GC apparatus equipped with a dual flame ionization detection system and fused-silica capillary columns (60 m × 0.22 mm I.D., film thickness 0.25μm), Rtx-1 (polydimethylsiloxane). The oven temperature was programmed from 60°C to 230°C at 2°C/min and then held isothermally at 230°C for 35 min. Injector and detector temperatures were maintained at 280°C. Samples were injected in the split mode (1/50), using helium as the carrier gas (1 mL/min); the injection volume was 0.2 μL. Retention indices (RIs) of the compounds were determined relative to the retention times of the series of n-alkanes (C5–C30) with linear interpolation, using the Van den Dool and Kratz equation and software from Perkin-Elmer [14]. Relative amounts of individual components were calculated on the basis of their GC peak areas on two capillary Rtx-1 and Rtx-Wax columns, without FID response factor correction.


### 2.4. Gas Chromatography-Mass Spectrometry Analysis

Samples were analyzed with a Perkin-Elmer Turbo mass detector (quadrupole), coupled to a Perkin-Elmer Autosystem XL, equipped with the fused-silica capillary columns Rtx-1 and Rtx-Wax (ion source temperature 150°C; energy ionization 70 eV). EI mass spectra were acquired over the mass range 35–350 Da (scan time: 1 s). Other GC conditions were the same as described under GC except split 1/80.


### 2.5. Component Identification

Identification of the components was based on (i) the comparison of their GC retention indices (RIs) on nonpolar columns, determined relatively by the retention time of a series of n-alkanes with linear interpolation, with those of authentic compounds or literature data [15–20]; (ii) computer matching with commercial mass spectral libraries [17–22] and comparison of spectra with those of our personal library. Relative amounts of individual components were calculated on the basis of their GC peak areas on the capillary Rtx-1 columns, without FID response factor correction.


### 2.6. Antimicrobial Activity

#### 2.6.1. Test Microorganisms

Bacillus cereus (ATCC 11778, gram positive), Staphylococcus aureus (ATCC 25925, gram positive), Escherichia coli (ATCC 9847, gram negative), and Candida albicans (IPP 444) microorganism strains were employed for determination of antimicrobial activity. Bacterial strains preserved in nutrient agar at 4°C were revivified in nutrient solution and incubated at 37 ± 1°C during 18 to 24 h. 0.1 mL of each culture was added to 10 mL OF BHIB (Brain Heart Infusion Broth, Pronadisa Hispanalab). C. albicans preserved at 4°C in the Sabouraud agar supplemented with chloramphenicol was revivified in nutrient solution and incubated at 30 ± 1°C during 24 to 48 h. 0.1 mL of each culture was added to 10 mL of sterile physiological water. For antimicrobial assay, bacterial strains were grown on Mueller-Hinton Agar (MHA, Pronadisa Hispanalab) while C. albicans was grown on Sabouraud Dextrose Agar + Chloramphenicol (SDA, Merck). Bacterial and yeast inocula reached microbial densities in the range 106 to 107 cfu/mL.


#### 2.6.2. Evaluation of Antimicrobial Activity

The essential oil (5μL) was applied on the paper discs (the disc diameter was 6 mm). Then disc papers were placed in the inoculated plates. After 24 h of incubation at 37°C, the diameters of growth inhibition zones were measured.


## 2.1. Plant Material

D. crinitus were collected in Chelaida forest area (at about 8 km northeast of Tlemcen, Algeria). Stems/leaves essential oils used for the comparative study were obtained from wild plants collected at the end of March (early vegetative), at mid-May (early flowering), and at the end of July (full flowering).


## 2.2. Essential Oil Extraction

D. crinitusessential oils were isolated by hydrodistillation (400–450 g of dried plant per sample) for 6 h using a Clevenger-type apparatus [13] according to the European Pharmacopoeia.


## 2.3. Gas Chromatography Analysis (GC)

GC analyses were carried out using a Perkin-Elmer (Waltham, MA, USA) Autosystem XL GC apparatus equipped with a dual flame ionization detection system and fused-silica capillary columns (60 m × 0.22 mm I.D., film thickness 0.25μm), Rtx-1 (polydimethylsiloxane). The oven temperature was programmed from 60°C to 230°C at 2°C/min and then held isothermally at 230°C for 35 min. Injector and detector temperatures were maintained at 280°C. Samples were injected in the split mode (1/50), using helium as the carrier gas (1 mL/min); the injection volume was 0.2 μL. Retention indices (RIs) of the compounds were determined relative to the retention times of the series of n-alkanes (C5–C30) with linear interpolation, using the Van den Dool and Kratz equation and software from Perkin-Elmer [14]. Relative amounts of individual components were calculated on the basis of their GC peak areas on two capillary Rtx-1 and Rtx-Wax columns, without FID response factor correction.


## 2.4. Gas Chromatography-Mass Spectrometry Analysis

Samples were analyzed with a Perkin-Elmer Turbo mass detector (quadrupole), coupled to a Perkin-Elmer Autosystem XL, equipped with the fused-silica capillary columns Rtx-1 and Rtx-Wax (ion source temperature 150°C; energy ionization 70 eV). EI mass spectra were acquired over the mass range 35–350 Da (scan time: 1 s). Other GC conditions were the same as described under GC except split 1/80.


## 2.5. Component Identification

Identification of the components was based on (i) the comparison of their GC retention indices (RIs) on nonpolar columns, determined relatively by the retention time of a series of n-alkanes with linear interpolation, with those of authentic compounds or literature data [15–20]; (ii) computer matching with commercial mass spectral libraries [17–22] and comparison of spectra with those of our personal library. Relative amounts of individual components were calculated on the basis of their GC peak areas on the capillary Rtx-1 columns, without FID response factor correction.


## 2.6. Antimicrobial Activity

### 2.6.1. Test Microorganisms

Bacillus cereus (ATCC 11778, gram positive), Staphylococcus aureus (ATCC 25925, gram positive), Escherichia coli (ATCC 9847, gram negative), and Candida albicans (IPP 444) microorganism strains were employed for determination of antimicrobial activity. Bacterial strains preserved in nutrient agar at 4°C were revivified in nutrient solution and incubated at 37 ± 1°C during 18 to 24 h. 0.1 mL of each culture was added to 10 mL OF BHIB (Brain Heart Infusion Broth, Pronadisa Hispanalab). C. albicans preserved at 4°C in the Sabouraud agar supplemented with chloramphenicol was revivified in nutrient solution and incubated at 30 ± 1°C during 24 to 48 h. 0.1 mL of each culture was added to 10 mL of sterile physiological water. For antimicrobial assay, bacterial strains were grown on Mueller-Hinton Agar (MHA, Pronadisa Hispanalab) while C. albicans was grown on Sabouraud Dextrose Agar + Chloramphenicol (SDA, Merck). Bacterial and yeast inocula reached microbial densities in the range 106 to 107 cfu/mL.


### 2.6.2. Evaluation of Antimicrobial Activity

The essential oil (5μL) was applied on the paper discs (the disc diameter was 6 mm). Then disc papers were placed in the inoculated plates. After 24 h of incubation at 37°C, the diameters of growth inhibition zones were measured.


## 2.6.1. Test Microorganisms

Bacillus cereus (ATCC 11778, gram positive), Staphylococcus aureus (ATCC 25925, gram positive), Escherichia coli (ATCC 9847, gram negative), and Candida albicans (IPP 444) microorganism strains were employed for determination of antimicrobial activity. Bacterial strains preserved in nutrient agar at 4°C were revivified in nutrient solution and incubated at 37 ± 1°C during 18 to 24 h. 0.1 mL of each culture was added to 10 mL OF BHIB (Brain Heart Infusion Broth, Pronadisa Hispanalab). C. albicans preserved at 4°C in the Sabouraud agar supplemented with chloramphenicol was revivified in nutrient solution and incubated at 30 ± 1°C during 24 to 48 h. 0.1 mL of each culture was added to 10 mL of sterile physiological water. For antimicrobial assay, bacterial strains were grown on Mueller-Hinton Agar (MHA, Pronadisa Hispanalab) while C. albicans was grown on Sabouraud Dextrose Agar + Chloramphenicol (SDA, Merck). Bacterial and yeast inocula reached microbial densities in the range 106 to 107 cfu/mL.


## 2.6.2. Evaluation of Antimicrobial Activity

The essential oil (5μL) was applied on the paper discs (the disc diameter was 6 mm). Then disc papers were placed in the inoculated plates. After 24 h of incubation at 37°C, the diameters of growth inhibition zones were measured.


## 3. Results and Discussion

### 3.1. Chemical Characterization

The variation of the essential oil yield of aerial parts ofD. crinitus with the three growth stages is shown in Table 1. A significant change in essential oil yield was observed during the different growth stages. During the early-vegetative stage, the essential oil yield was of 0.02%. At the early-flowering stage, the essential oil yield increased and reached 0.05%. At full-flowering stages, the essential oil yield increased significantly to reach 0.15% (Table 1).Table 1
Plant material, dates, vegetative cycle and oil yields ofD. crinitus.
Harvest  dates
Vegetative cycle
Essential oil yield (%)
Temperature (°C)
28/03/2009
Early vegetative
0.02
16
16/05/2009
Early flowering
0.05
28
28/07/2009
Full flowering
0.15
37Variation in oil yield can be attributed to many factors, such as the genetic factors, the developmental stage, the extraction method, and the pedoclimatic conditions [23, 24]. It seems that oil yield during plant growth is particularly sensitive to environmental conditions (light, nutrient availability, and day length) [25, 26].All three oils were analyzed by GC and GC-MS and their chemical compositions are presented in Table2, 18 sesquiterpene hydrocarbons, 9 hydrocarbons monoterpene, 5 oxygenated monoterpenes, 5 phenolic compounds, 4 oxygenated sesquiterpenes, 2 oxygenated diterpenes, and 01 diterpene hydrocarbons.However, in the early-vegetative stage 56 components accounting for 93.8% of the total composition were identified. The most abundant chemical groups of this oil were aliphatic compounds (49.9%), phenolic compounds (36.4%), sesquiterpene hydrocarbons (4.3%), and oxygenated sesquiterpenes (2.1%). The main aliphatic compounds components were decanol (10.4%), heptadecane (9.8%), dodecanal (6.3%), pentadecane (5.4%), undecane (4.0%), followed by decanal (2.7%), hexadecane (1.8), hexadecanoic acid (1.5%), and hexadecanal (1.1%). However, isochavicol isobutyrate (26.4%) and isochavicol 2-methyl butyrate (7.9%) were the major constituent of phenolic compounds. The terpenic compounds were represented only by α-humulene (1.9%), geranyl butyrate (1.2%), and α-cedrol (1.2%). Regarding the early-flowering stage, the composition of essential oil is similar from a qualitative point of view with that observed in the early-vegetative stage, characterized by high percentage of phenolic compounds (54.0%) but with a slight difference in oil composition. We noted the presence of zizaene (2.3%), caryophyllene oxide (2.1%), bornyl acetate (2.1%), and myrcene (1.4%). On the other hand, the oil produced in full-flowering stage was characterized by isochavicol isobutyrate (76.1%), isochavicol 2-methyl butyrate (5.4%), myrcene (1.9%), zizaene (3.1%), limonene (1.5%), and dodecyl pentanoate (1.3%).Table 2
Chemical compositions ofD. crinitus essential oils (%) during three developmental stages.
N
°
a
Componentsb
I
l
c
I
a
d
I
II
III
1
Nonane
900
900
tr
—
—
2
α-pinene
936
931
—
0.6
0.5
3
Sabinene
973
966
—
0.1
tr
4
β-pinene
978
971
—
0.1
tr
5
Myrcene
987
981
—
1.4
1.9
6
Decane
1000
1000
tr
0.1
0.1
7
p-cymene
1015
1012
—
0.1
0.1
8
1,8 Cineole
1024
1020
—
0.6
0.5
9
Limonene
1025
1026
—
0.6
1.5
10
(E)-β-ocimene
1041
1037
—
0.1
0.1
11
γ-terpinene
1051
1049
tr
0.1
0.1
12
1-Octanol
1061
1056
0.1
tr
tr
13
2-Methyl-Decane
1068
1065
—
tr
0.1
14
Nonanal
1076
1074
0.2
0.1
tr
15
α-Terpinolene
1082
1079
0.2
tr
0.1
16
Linalool
1086
1086
0.2
tr
0.1
17
Undecane
1100
1100
4.0
0.1
tr
18
2-Ethyl-hexyl acetate
1144
1149
0.2
0.4
0.1
19
Terpinen-4-ol
1164
1161
0.1
0.1
0.1
20
Decanal
1188
1187
2.7
0.5
0.2
21
Dodecane
1200
1198
0.2
tr
tr
22
Decanol
1263
1259
10.4
2.1
0.7
23
Nonanoic acid
1263
1263
0.1
tr
tr
24
Bornyl acetate
1270
1269
0.1
2.1
0.7
25
Undecanal
1290
1280
0.4
0.2
tr
26
Tridecane
1300
1300
0.4
tr
tr
27
n-Octyl isobutyrate
1329
1325
tr
tr
0.2
28
Neryl acetate
1342
1336
—
0.1
tr
29
Decanoic acid
1347
1348
0.6
0.2
tr
30
Benzyl 2-methyl butyrate
1360
1352
0.6
0.2
tr
31
Undecanol
1367
1367
0.8
0.4
0.1
32
α-copaene
1379
1386
0.1
0.1
tr
33
β-Bourbonene
1386
1376
—
0.1
0.1
34
Dodecanal
1389
1390
6.3
7.3
0.2
35
Tetradecane
1400
1403
0.3
tr
tr
36
Longifolene
1411
1409
0.1
0.1
tr
37
α-Santalene
1422
1415
0.1
0.4
0.4
38
β-Caryophyllene
1420
1424
0.1
tr
tr
39
Dauca-3,8-diene
1428
1426
0.1
tr
tr
40
trans-α-Bergamotene
1432
1431
0.2
tr
tr
41
(E)-β-Farnesene
1448
1449
—
tr
tr
42
α-Humulene
1456
1451
1.9
0.5
tr
43
Zizaene
1456
1463
—
2.3
3.1
44
Dodecanol
1472
1470
2.7
0.5
0.4
45
α-Curcumene
1473
1474
0.1
0.4
0.4
46
Germacrene-D
1479
1478
0.2
tr
tr
47
β-Selinene
1486
1480
0.1
tr
tr
48
Zingiberene
1489
1483
tr
tr
0.1
49
Pentadecane
1500
1500
5.4
1.1
0.1
50
γ-Cadinene
1516
1513
0.1
0.1
tr
51
Geranyl butyrate
1534
1530
1.2
2.1
0.5
52
Isochavicol isobutyrate
1546
1541
26.4
41.4
76.1
53
(Z)-3-Hexenyl benzoate
1545
1557
0.8
0.3
tr
54
Dodecanoic acid
1554
1560
0.6
0.4
tr
55
Caryophyllene oxide
1576
1572
0.6
2.1
0.1
56
Dodecyl acetate
1585
1580
—
0.4
0.1
57
Hexadecane
1600
1599
1.8
1.9
0.2
58
α-Cedrol
1603
1596
1.2
5.0
0.1
59
Isochavicol 2-methyl butyrate
1651
1648
7.9
11.3
5.4
60
α-Bisabolol
1672
1667
0.1
0.9
0.2
61
Heptadecane
1700
1700
9.8
2.9
0.1
62
Benzyl benzoate
1730
1723
0.7
0.8
0.6
63
Tetradecanoic acid
1761
1756
0.1
0.3
0.1
64
Hexadecanal
1782
1787
1.1
0.5
0.1
65
Lactarazulene
1796
1792
tr
0,5
0.1
66
Neophytadiene
1807
1807
0.1
0.5
0.1
67
Phytone
1833
1835
0.2
0.1
0.2
68
Dodecyl pentanoate
1843
1840
0.2
0.1
1.3
69
Isophytol
1946
1944
—
tr
0.1
70
Hexadecanoic acid
1951
1949
1.5
0.1
tr
71
(E) Phytol
2114
2102
0.4
0.5
tr
Total
93.8
95.3
97.4
Aliphatic compounds
49.9
19.6
3.7
Phenolic compounds
36.4
54
82.1
Monoterpene hydrocarbons
0.2
3.1
4.3
Oxygenated monoterpenes
0.4
2.9
1.4
Sesquiterpene hydrocarbons
4.3
6.6
5.1
Oxygenated sesquiterpenes
2.1
8.1
0.6
Diterpene hydrocarbons
0.1
0.5
0.1
Oxygenated diterpenes
0.4
0.5
0.1
aOrder of elution is given on apolar column (Rtx-1). bRetention indices of literature on the apolar column (lRIa). cRetention indices on the apolar Rtx-1 column (RIa). tr: trace, (<0.05%). Vegetative cycle—I: early vegetative; II: early flowering; III: full flowering.A comparison of chemical compositions ofD. crinitus essential oils obtained from three stages of development shows significant differences. Phenolic compounds were the most abundant components identified in aerial parts of D. crinitus. The amount of isochavicol isobutyrate significantly increased to early-flowering and full-flowering stages (41.4% and 76.1%, resp.). Relative to early-vegetative stage, the fraction of terpenic hydrocarbons was increased, mainly due to an increase of zizaene, myrcene, and limonene percentages in the full-flowering and early-flowering stages. However, fraction of aliphatic compounds was higher at the early-vegetative stage (49.9% of total oil, resp.), while its level decreased to 19.6% at the early-flowering stage and then to 3.6% at the full-flowering stage. According to our results, it seems that chemical composition of D. crinitus essential oil varied significantly with the physiological stage of the plant. Along the vegetative life of the plant, D. crinitus produces three essential oils which differed by the percentage of their class compounds. (Figure 1).Figure 1
Percentage variation of the mainD. crinitus classes of compounds throughout the vegetative cycle.


### 3.2. Antimicrobial Activity

Moreover, the antibacterial activity of essential oil of the three vegetative stages was assessed by disc diffusion assay. The results indicated in Table3 and in the paper represent the net zone of inhibition including the diameter (6 mm) of the paper disk. Biological activity was affected to essential oil as follows: strong activity: inhibition zone >20 mm, moderate activity: inhibition zone <20–12 mm and no inhibition: zone <12 mm. As shown in Table 3, the diameters of the inhibition zones of the studied essential oils ranged from 6 to 30 mm with the highest inhibition zone values observed against the medically important pathogens C. albicans (30 mm) and S. aureus (28 mm). C. albicans is a microbe responsible for most clinical yeast infections, for example, in mouth infections. However, in early-flowering and full-flowering stages, the essential oils have a strong antibacterial activity against S. aureus with diameters of inhibition zones of 21 and 28 mm, respectively. The other bacterial strains (E. coli and B. cereus) showed no inhibition, with diameters of inhibition zones ranging from 6 to 10 mm (Table 3).Table 3
Antimicrobial activity of the essential oils of aerial parts ofD. crinitus.
Microorganisms
Diameters of inhibition (mm)
Early vegetative
Early flowering
Full flowering
Gram-positive bacterium
Bacillus cereus
8
11
6
Staphylococcus aureus
9
21
28
Gram-negative bacterium
Escherichia   coli
10
8
6
Yeast
Candida albicans
30
30
30From all the used species,S. aureus is one of the most common of the gram-positive bacteria that causes food poisonings. Its source is not the food itself but the humans who contaminate foods after they have been processed [27]. These observations may be attributed to the nature of biologically active components. Indeed, various chemical compounds have direct activity against many species of bacteria, such as terpenes and a variety of aliphatic hydrocarbons (alcohols, aldehydes, and ketones). The lipophilic character of their hydrocarbon skeleton and the hydrophilic character of their functional groups are of main importance in the antimicrobial action of essential oils components. Therefore, a rank of activity has been proposed as follows: phenols > aldehydes > ketones > alcohols > esters > hydrocarbons [28]. For example, some essential oils containing phenolic structures are highly active against a broad spectrum of microorganisms [28, 29]. The importance of the hydroxyl group has been confirmed [30, 31]. Aldehydes are known to possess powerful antimicrobial activity. It has been proposed that an aldehyde group conjugated to a carbon-to-carbon double bond is a highly electronegative arrangement, which may explain their activity [32], suggesting a proportional increase of the antibacterial activity with electronegativity [33, 34]. Aliphatic alcohols were reported to possess strong-to-moderate activities against several bacteria. The activity increased with the length of the carbon chain [35]. Terpenic compounds have also shown antimicrobial properties that appear to have strong-to-moderate antibacterial activity against Gram-positive bacteria and against pathogenic fungi, but in general, weaker activity was observed against Gram-negative bacteria [36, 37]. Secondly there is some evidence that minor components have a critical part to play in antibacterial activity, possibly by producing a synergistic effect between other components. This has been found to be the case for sage [38], some species of Thymus [39] and oregano [40].


## 3.1. Chemical Characterization

The variation of the essential oil yield of aerial parts ofD. crinitus with the three growth stages is shown in Table 1. A significant change in essential oil yield was observed during the different growth stages. During the early-vegetative stage, the essential oil yield was of 0.02%. At the early-flowering stage, the essential oil yield increased and reached 0.05%. At full-flowering stages, the essential oil yield increased significantly to reach 0.15% (Table 1).Table 1
Plant material, dates, vegetative cycle and oil yields ofD. crinitus.
Harvest  dates
Vegetative cycle
Essential oil yield (%)
Temperature (°C)
28/03/2009
Early vegetative
0.02
16
16/05/2009
Early flowering
0.05
28
28/07/2009
Full flowering
0.15
37Variation in oil yield can be attributed to many factors, such as the genetic factors, the developmental stage, the extraction method, and the pedoclimatic conditions [23, 24]. It seems that oil yield during plant growth is particularly sensitive to environmental conditions (light, nutrient availability, and day length) [25, 26].All three oils were analyzed by GC and GC-MS and their chemical compositions are presented in Table2, 18 sesquiterpene hydrocarbons, 9 hydrocarbons monoterpene, 5 oxygenated monoterpenes, 5 phenolic compounds, 4 oxygenated sesquiterpenes, 2 oxygenated diterpenes, and 01 diterpene hydrocarbons.However, in the early-vegetative stage 56 components accounting for 93.8% of the total composition were identified. The most abundant chemical groups of this oil were aliphatic compounds (49.9%), phenolic compounds (36.4%), sesquiterpene hydrocarbons (4.3%), and oxygenated sesquiterpenes (2.1%). The main aliphatic compounds components were decanol (10.4%), heptadecane (9.8%), dodecanal (6.3%), pentadecane (5.4%), undecane (4.0%), followed by decanal (2.7%), hexadecane (1.8), hexadecanoic acid (1.5%), and hexadecanal (1.1%). However, isochavicol isobutyrate (26.4%) and isochavicol 2-methyl butyrate (7.9%) were the major constituent of phenolic compounds. The terpenic compounds were represented only by α-humulene (1.9%), geranyl butyrate (1.2%), and α-cedrol (1.2%). Regarding the early-flowering stage, the composition of essential oil is similar from a qualitative point of view with that observed in the early-vegetative stage, characterized by high percentage of phenolic compounds (54.0%) but with a slight difference in oil composition. We noted the presence of zizaene (2.3%), caryophyllene oxide (2.1%), bornyl acetate (2.1%), and myrcene (1.4%). On the other hand, the oil produced in full-flowering stage was characterized by isochavicol isobutyrate (76.1%), isochavicol 2-methyl butyrate (5.4%), myrcene (1.9%), zizaene (3.1%), limonene (1.5%), and dodecyl pentanoate (1.3%).Table 2
Chemical compositions ofD. crinitus essential oils (%) during three developmental stages.
N
°
a
Componentsb
I
l
c
I
a
d
I
II
III
1
Nonane
900
900
tr
—
—
2
α-pinene
936
931
—
0.6
0.5
3
Sabinene
973
966
—
0.1
tr
4
β-pinene
978
971
—
0.1
tr
5
Myrcene
987
981
—
1.4
1.9
6
Decane
1000
1000
tr
0.1
0.1
7
p-cymene
1015
1012
—
0.1
0.1
8
1,8 Cineole
1024
1020
—
0.6
0.5
9
Limonene
1025
1026
—
0.6
1.5
10
(E)-β-ocimene
1041
1037
—
0.1
0.1
11
γ-terpinene
1051
1049
tr
0.1
0.1
12
1-Octanol
1061
1056
0.1
tr
tr
13
2-Methyl-Decane
1068
1065
—
tr
0.1
14
Nonanal
1076
1074
0.2
0.1
tr
15
α-Terpinolene
1082
1079
0.2
tr
0.1
16
Linalool
1086
1086
0.2
tr
0.1
17
Undecane
1100
1100
4.0
0.1
tr
18
2-Ethyl-hexyl acetate
1144
1149
0.2
0.4
0.1
19
Terpinen-4-ol
1164
1161
0.1
0.1
0.1
20
Decanal
1188
1187
2.7
0.5
0.2
21
Dodecane
1200
1198
0.2
tr
tr
22
Decanol
1263
1259
10.4
2.1
0.7
23
Nonanoic acid
1263
1263
0.1
tr
tr
24
Bornyl acetate
1270
1269
0.1
2.1
0.7
25
Undecanal
1290
1280
0.4
0.2
tr
26
Tridecane
1300
1300
0.4
tr
tr
27
n-Octyl isobutyrate
1329
1325
tr
tr
0.2
28
Neryl acetate
1342
1336
—
0.1
tr
29
Decanoic acid
1347
1348
0.6
0.2
tr
30
Benzyl 2-methyl butyrate
1360
1352
0.6
0.2
tr
31
Undecanol
1367
1367
0.8
0.4
0.1
32
α-copaene
1379
1386
0.1
0.1
tr
33
β-Bourbonene
1386
1376
—
0.1
0.1
34
Dodecanal
1389
1390
6.3
7.3
0.2
35
Tetradecane
1400
1403
0.3
tr
tr
36
Longifolene
1411
1409
0.1
0.1
tr
37
α-Santalene
1422
1415
0.1
0.4
0.4
38
β-Caryophyllene
1420
1424
0.1
tr
tr
39
Dauca-3,8-diene
1428
1426
0.1
tr
tr
40
trans-α-Bergamotene
1432
1431
0.2
tr
tr
41
(E)-β-Farnesene
1448
1449
—
tr
tr
42
α-Humulene
1456
1451
1.9
0.5
tr
43
Zizaene
1456
1463
—
2.3
3.1
44
Dodecanol
1472
1470
2.7
0.5
0.4
45
α-Curcumene
1473
1474
0.1
0.4
0.4
46
Germacrene-D
1479
1478
0.2
tr
tr
47
β-Selinene
1486
1480
0.1
tr
tr
48
Zingiberene
1489
1483
tr
tr
0.1
49
Pentadecane
1500
1500
5.4
1.1
0.1
50
γ-Cadinene
1516
1513
0.1
0.1
tr
51
Geranyl butyrate
1534
1530
1.2
2.1
0.5
52
Isochavicol isobutyrate
1546
1541
26.4
41.4
76.1
53
(Z)-3-Hexenyl benzoate
1545
1557
0.8
0.3
tr
54
Dodecanoic acid
1554
1560
0.6
0.4
tr
55
Caryophyllene oxide
1576
1572
0.6
2.1
0.1
56
Dodecyl acetate
1585
1580
—
0.4
0.1
57
Hexadecane
1600
1599
1.8
1.9
0.2
58
α-Cedrol
1603
1596
1.2
5.0
0.1
59
Isochavicol 2-methyl butyrate
1651
1648
7.9
11.3
5.4
60
α-Bisabolol
1672
1667
0.1
0.9
0.2
61
Heptadecane
1700
1700
9.8
2.9
0.1
62
Benzyl benzoate
1730
1723
0.7
0.8
0.6
63
Tetradecanoic acid
1761
1756
0.1
0.3
0.1
64
Hexadecanal
1782
1787
1.1
0.5
0.1
65
Lactarazulene
1796
1792
tr
0,5
0.1
66
Neophytadiene
1807
1807
0.1
0.5
0.1
67
Phytone
1833
1835
0.2
0.1
0.2
68
Dodecyl pentanoate
1843
1840
0.2
0.1
1.3
69
Isophytol
1946
1944
—
tr
0.1
70
Hexadecanoic acid
1951
1949
1.5
0.1
tr
71
(E) Phytol
2114
2102
0.4
0.5
tr
Total
93.8
95.3
97.4
Aliphatic compounds
49.9
19.6
3.7
Phenolic compounds
36.4
54
82.1
Monoterpene hydrocarbons
0.2
3.1
4.3
Oxygenated monoterpenes
0.4
2.9
1.4
Sesquiterpene hydrocarbons
4.3
6.6
5.1
Oxygenated sesquiterpenes
2.1
8.1
0.6
Diterpene hydrocarbons
0.1
0.5
0.1
Oxygenated diterpenes
0.4
0.5
0.1
aOrder of elution is given on apolar column (Rtx-1). bRetention indices of literature on the apolar column (lRIa). cRetention indices on the apolar Rtx-1 column (RIa). tr: trace, (<0.05%). Vegetative cycle—I: early vegetative; II: early flowering; III: full flowering.A comparison of chemical compositions ofD. crinitus essential oils obtained from three stages of development shows significant differences. Phenolic compounds were the most abundant components identified in aerial parts of D. crinitus. The amount of isochavicol isobutyrate significantly increased to early-flowering and full-flowering stages (41.4% and 76.1%, resp.). Relative to early-vegetative stage, the fraction of terpenic hydrocarbons was increased, mainly due to an increase of zizaene, myrcene, and limonene percentages in the full-flowering and early-flowering stages. However, fraction of aliphatic compounds was higher at the early-vegetative stage (49.9% of total oil, resp.), while its level decreased to 19.6% at the early-flowering stage and then to 3.6% at the full-flowering stage. According to our results, it seems that chemical composition of D. crinitus essential oil varied significantly with the physiological stage of the plant. Along the vegetative life of the plant, D. crinitus produces three essential oils which differed by the percentage of their class compounds. (Figure 1).Figure 1
Percentage variation of the mainD. crinitus classes of compounds throughout the vegetative cycle.


## 3.2. Antimicrobial Activity

Moreover, the antibacterial activity of essential oil of the three vegetative stages was assessed by disc diffusion assay. The results indicated in Table3 and in the paper represent the net zone of inhibition including the diameter (6 mm) of the paper disk. Biological activity was affected to essential oil as follows: strong activity: inhibition zone >20 mm, moderate activity: inhibition zone <20–12 mm and no inhibition: zone <12 mm. As shown in Table 3, the diameters of the inhibition zones of the studied essential oils ranged from 6 to 30 mm with the highest inhibition zone values observed against the medically important pathogens C. albicans (30 mm) and S. aureus (28 mm). C. albicans is a microbe responsible for most clinical yeast infections, for example, in mouth infections. However, in early-flowering and full-flowering stages, the essential oils have a strong antibacterial activity against S. aureus with diameters of inhibition zones of 21 and 28 mm, respectively. The other bacterial strains (E. coli and B. cereus) showed no inhibition, with diameters of inhibition zones ranging from 6 to 10 mm (Table 3).Table 3
Antimicrobial activity of the essential oils of aerial parts ofD. crinitus.
Microorganisms
Diameters of inhibition (mm)
Early vegetative
Early flowering
Full flowering
Gram-positive bacterium
Bacillus cereus
8
11
6
Staphylococcus aureus
9
21
28
Gram-negative bacterium
Escherichia   coli
10
8
6
Yeast
Candida albicans
30
30
30From all the used species,S. aureus is one of the most common of the gram-positive bacteria that causes food poisonings. Its source is not the food itself but the humans who contaminate foods after they have been processed [27]. These observations may be attributed to the nature of biologically active components. Indeed, various chemical compounds have direct activity against many species of bacteria, such as terpenes and a variety of aliphatic hydrocarbons (alcohols, aldehydes, and ketones). The lipophilic character of their hydrocarbon skeleton and the hydrophilic character of their functional groups are of main importance in the antimicrobial action of essential oils components. Therefore, a rank of activity has been proposed as follows: phenols > aldehydes > ketones > alcohols > esters > hydrocarbons [28]. For example, some essential oils containing phenolic structures are highly active against a broad spectrum of microorganisms [28, 29]. The importance of the hydroxyl group has been confirmed [30, 31]. Aldehydes are known to possess powerful antimicrobial activity. It has been proposed that an aldehyde group conjugated to a carbon-to-carbon double bond is a highly electronegative arrangement, which may explain their activity [32], suggesting a proportional increase of the antibacterial activity with electronegativity [33, 34]. Aliphatic alcohols were reported to possess strong-to-moderate activities against several bacteria. The activity increased with the length of the carbon chain [35]. Terpenic compounds have also shown antimicrobial properties that appear to have strong-to-moderate antibacterial activity against Gram-positive bacteria and against pathogenic fungi, but in general, weaker activity was observed against Gram-negative bacteria [36, 37]. Secondly there is some evidence that minor components have a critical part to play in antibacterial activity, possibly by producing a synergistic effect between other components. This has been found to be the case for sage [38], some species of Thymus [39] and oregano [40].


## 4. Conclusions

In conclusion, CG and CG-MS analysis showed that oils ofD. crinitus are rich in phenolic compounds, whereas terpenic compounds showed marked variation with plant growth stage and the maximum amounts were detected during full-flowering stage. However, phenolic and aliphatic compounds were the main components during the early-vegetative stage. Bioassay screening of oils showed strong activity against C. albicans and S. aureus. The results of the current study have shown that D. crinitus essential oil is potentially a good source of antimicrobial compounds and support the traditional medicinal application of this plant.



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*Source: 149502-2012-07-26.xml*