In this work, free volatile compounds were isolated from dried aerial parts of
D. viscosa by water distillation in a Clevenger-type apparatus. The lipophilic (essential oil) and hydrofracture (hydrosol) collected from the inner tube of the Clevenger apparatus differ in chemical composition and biological activity due to the difference in solubility of the volatile compounds. In addition to water distillation, some authors have performed steam distillation, solvent extraction, and extraction by ultrasonic distillation from plant material of the genus Inula
[8,9,10][8][9][10]. They obtained significant differences in the yield and composition of the essential oil
[8]. In our study, the volatile compounds in the pentane layer (essential oil) and volatile compounds in the aqueous phase (hydrosol) were analyzed. The total oil yield was 0.09%, based on the dry weight of the samples. The composition and relative amounts of the compounds in both layers are shown in
Table 1. Lipophilic compounds dissolved in pentane were analyzed by GC-MS. GC-MS analysis of the aqueous layer identified the more hydrophilic volatile components. Components that are soluble in both water and organic solvents were detected in the water and pentane layers (
Table 1). Thus, GC-MS analysis of both phases, coupled with HPLC analysis of the hydrosol, provides us with a more complete phytochemical composition of the volatiles of this plant species. Haoui et al.
[10] found that monoterpenes were the major chemical class of the essential oil of
D. viscosa from Turkey and Algeria, while the class of oxygenated sesquiterpenes predominated in the plants from Spain, Italy, France, and Jordan
[10]. In our study, twenty compounds, divided into six classes, and seventeen compounds, divided into three classes, were identified in the essential oil (EO) and hydrosol, accounting for 96.74% and 96.90% of the total oil and hydrosol composition, respectively. In terms of compound classes, the oxygenated monoterpenes dominate in the EO and hydrosol samples, accounting for 53.41% and 81.85% of the total composition, respectively. In addition to the oxygenated monoterpenes
1,8-cineole identified as the dominant compound in the oil (16.41%) and
α-terpinyl acetate (13.92%), the oxygenated sesquiterpenes caryophyllene oxide (15.14%) and
α-muurolol (13.75%) stand out in the overall composition of the oil of
D. viscosa (
Table 1).
1,8-Cineole (18.55%) represents the second most abundant component in the total hydrosol composition, and the compounds
α-muurolol and caryophyllene oxide were also identified as frequent compounds in the hydrosol composition with proportions of 10.25% and 3.24%, respectively (
Table 1). The oxygenated monoterpene
p-menth-1-en-9-ol dominated the overall hydrosol composition (29.93%), while this compound was not detected in the oil composition. Linalool (11.67%) and
cis-sabinene hydrate (10.97%) were also identified at a high percentage in the hydrosol and are also among the abundant components in the essential oil composition with proportions of 6.62% and 4.23%, respectively (
Table 1). The oil contains a total of 30.11% oxygenated sesquiterpenes, with caryophyllene oxide (15.14%) and
α-muurolol (13.75%) being the dominant compounds in this class and cyperotundone (1.22%) being less abundant. Madani et al.
[30] compiled a table of the main components of the essential oils of
D. viscosa from Algeria, Jordan, Italy, Turkey, Spain, and France. The composition of the oil of
D. viscosa from Sardinia is most similar to the composition of the oil of Croatian
D. viscosa in terms of caryophyllene oxide content. Caryophyllene oxide is also the main component obtained by water distillation from the leaves of this species from Algeria and Tunisia
[30,31][30][31]. The fatty acid and hydrocarbon groups represent less than 6% of the total oil (
Table 1). Differences in the composition of free volatiles of the species
D. viscosa are influenced by population diversity, the time of collection of the plant material, and isolation techniques. We identified volatiles from two phases and, as shown in
Table 1, some compounds were detected in both the lipophilic and aqueous phases, but some were identified in only one phase. This approach has given us a more complete insight into the chemical composition and potential application of specialized metabolites of the species
D. viscosa.