## 2 Results and Discussion
### Chemical Composition of Essential Oils and Hydrolats by GC-MS
Regarding the other two species (_Eucalyptus pulverulenta_ Sims and _Eucalyptus pulverulenta_ baby blue Sims), the \(\alpha\)-pinene amount was approximately half the Limonene, with lower amounts of \(p\)-cymene, \(\beta\)-myrcene, and \(\beta\)-pinene. Other MH (camphene, \(\alpha\)-phellandrene, alloocimene) were in low amounts. Noteworthy, the \(\alpha\)-phellandrene content in EOs of all these species was lower than 1%, according to the _European Pharmacopoeia_ specification for 1,8-cineol-rich \(E\). oils [16]. 1,8-cineole (eucalyptol) was by far the main component of the analyzed samples (see the next paragraphs); however, the differences in relative abundance of metabolites present in low amount, or even in trace, play a critical role in mediating different activities for EOs from different _Eucalyptus_ species with 1,8-cineole as the main component; indeed, these different activities (i.e., alleophatic [24], protection against _Parthinium hysterophorus_ L. [25]) were reported as only due to differences in the relative abundance of minor components [24; 25], likely due to the synergistic effect of these latter compounds with other components [26; 27]. Regarding the hydrosols, no significant amounts of MH were detected, due to the hydrophobic nature of these molecules. Oxygenated monoterpenes (OM): 1,8-cineole is the main component of EOs obtained from the leaves of _Eucalyptus globulus_, the most common _Eucalyptus_ species [20]. In EOs from these four species, relative abundance of 1,8-cineole ranged between 83.80% and 88.66%, higher than the 80-85% indicated by the standard ISO as the minimum amount of 1,8-cineole for EO from _E. globulus_. Other papers in the literature reported the characterization of EOs from _Eucalyptus_[16; 17; 18] and _Eucalyptus pulverulenta_[16], while, to the authors' knowledge, no reports on EO from _Eucalyptus parvula_ have been published, to date. In such papers, the relative abundance of 1,8-cineole showed great variability ranging usually from 58.0 to 69.0% and sometimes reaching 87.8% in _E. cinerea_ EOs and being approx. 75% in _E. pulverulenta_ EOs. Consequently, also the relative abundances of the other minor terpenes showed a great variability. This variability might be due to the effect of climatic and geographical factors and harvesting season. In our study, _Eucalyptus parvula_ and _Eucalyptus pulverulenta_ Sims were the species with the highest amount of 1,8-cineole. Since EOs are totally composed by the volatile fraction, the relative abundance of each compound can be assumed as the amount of this molecule in the oil expressed as g/100g. Regarding the analyzed hydrosols (EWs), 1,8-cineole was in the range 88.40-90.78%. In order to better characterize these hydrosols, 1,8-cineole was quantified using an external calibration curve, as reported in the experimental section. Table 2 shows that the absolute concentration of 1,8-cineole in the EWs extracts varied in the range 0.74-1.58 g/L, highlighting that this molecule was also recovered in water samples. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Kind of Sample** & **1,8-cineole (g/L)** \\ \hline
1-16-EW & hydrosol & 1.58 a \\
2-16-EW & hydrosol & 1.45 b \\
3-16-EW & hydrosol & 1.52 a \\
4-16-EW & hydrosol & 0.74 e \\
1-17-EW & hydrosol & 0.86 d \\
1-1617-EW & hydrosol & 1.20 c \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Content of 1,8-cineole in the hydrosols by GC-MS analysis. Data are expressed in g/L as mean of three independent determinations (SD < 3%). Different letters indicate significant differences at \(p<0.05\). In EWs, OMs constituted 98-99% of the total VOCs, according to their water solubility, higher than MHs. Regarding OMs other than 1,8-cineole, in our samples \(\alpha\)-terpineol was the most abundant one (4.19-6.24%), followed by lower amounts of terpinen-4-ol, linalool oxides (furanoid, _cis_ and _trans_), terpineol isomer, and other minor OMs (<1.5%). OMs constituted about 90% of the EOs. In these samples, \(\alpha\)-terpineol was in the range 2.00-3.11%.