## 2 Results and Discussion  
### Optimum Extraction Yield and Total Phenolic Content  
The actual (experimental) and predicted values for the extraction yields and total phenolic content (TPC) can be seen in Table 1. For the aboveground part, the highest extraction yield of 87.19% was obtained at a temperature of 200 \({}^{\circ}\)C, 180 min residence time, and a water/plant ratio of 0.25. For the roots, the highest extraction yield of 72.6% was obtained at a temperature at the same set of conditions. Therefore, it appears that the aboveground part contains a significantly higher content of total extractables. Both Equations (1) and (5) highlight that temperature (A) was the most influential parameter in the extraction process, as shown by the coefficients of 11.60 and 13.95, respectively. Furthermore, the positive sign for these coefficients showed that temperature had a positive linear effect, indicating that higher temperatures resulted in higher extraction yields. This may be attributed to the higher solubility of the essential oil components at elevated temperatures [38]. Furthermore, the vapor pressure of subcritical water should also be considered an important factor for extraction. Higher vapor pressure at higher temperature promotes penetration of the water molecules through the sample matrix, while the higher diffusivity of subcritical water and lower surface tension enhances the transport of the essential oil components into the bulk water phase resulting in higher extraction efficiency [39]. The second most influential parameter was extraction time (B), followed by the water/plant ratio (C). Interestingly, opposite trends were observed for the aboveground part and roots with respect to the water/plant ratio. Increasing the water/plant ratio had a slightly negative impact on the extraction yield of the aboveground part and a slightly positive one for the roots. This may be attributed to the different recalcitrance to degradation of components found in the aboveground part but not present in the roots. This hypothesis will be further investigated later in Section 3.5 where the composition of the extracts is discussed. Furthermore, data were analyzed using the variance analysis (ANOVA), and the results are presented in Table 2. The regression coefficient (R\({}^{2}\)) can be used to evaluate \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Extraction Yield** & **Sum of** & **df** & **Mean** & **\(F\)-Value** & \(p\)**-Value** \\ \multicolumn{6}{l}{**(Aboveground Part)**} \\ \hline A\({}^{2}\) & 21.23 & 1 & 21.23 & 2.88 & 0.1505 \\ \hline B\({}^{2}\) & 20.44 & 1 & 20.44 & 2.77 & 0.1568 \\ \hline C\({}^{2}\) & 20.62 & 1 & 20.62 & 2.80 & 0.1554 \\ \hline Residual & 36.87 & 5 & 7.37 & & \\ \hline Cor Total & 1808.37 & 14 & & & \\ \hline R\({}^{2}\) & 0.9796 & & & & \\ \hline CV \% & 4.15 & & & & \\ \hline Extraction yield & & & & & \\ (roots) & & & & & \\ \hline Model & 1965.28 & 9 & 218.36 & 14.57 & 0.0044 \\ \hline A—temperature & 1556.26 & 1 & 1556.26 & 103.81 & 0.0002 \\ \hline B—extraction time & 164.35 & 1 & 164.35 & 10.96 & 0.0212 \\ \hline C—water/plant ratio & 38.46 & 1 & 38.46 & 2.57 & 0.1701 \\ \hline AB & 6.68 & 1 & 6.68 & 0.45 & 0.5339 \\ \hline AC & 3.78 & 1 & 3.78 & 0.25 & 0.6368 \\ \hline BC & 28.89 & 1 & 28.89 & 1.93 & 0.2238 \\ \hline A\({}^{2}\) & 70.58 & 1 & 70.58 & 4.71 & 0.0822 \\ \hline B\({}^{2}\) & 13.37 & 1 & 13.37 & 0.89 & 0.3883 \\ \hline C\({}^{2}\) & 82.86 & 1 & 82.86 & 5.53 & 0.0655 \\ \hline Residual & 74.96 & 5 & 14.99 & & \\ \hline Cor Total & 2040.24 & 14 & & & \\ \hline R\({}^{2}\) & 0.9633 & & & & \\ \hline CV \% & 7.57 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._the fit of the model. The ANOVA revealed that the aboveground part and root R\({}^{2}\) values were 0.9796 and 0.9633, respectively. According to these values, the proposed mathematical models account for more than 97.96 and 96.33% of the response's overall variation for the aboveground part and roots, respectively.