## 2 Results and Discussion
### Multiple Regression Modelling of the Total Phenol Content and Analysis of Variance  
The TPC experimental values (Table 1) for the aboveground part and roots were subjected to regression analysis and the following empirical relationships between the TPC and the independent variables (A: temperature, B: extraction time, and C: water/plant ratio) were obtained:  
\[ \begin{split} TPC\ (aboveground\ part)\\ =+57.84+18.97A+5.40B-58.95C-3.02 AB-14.84 AC\\ -18.70 BC-15.14A^{2}-0.83B^{2}+44.52C^{2}\\ TPC\ (roots)=+72.33+10.16A+1.77B-61.23C-2.90 AB-6.34 AC\\ -1.20 BC-10.41A^{2}+1.07B^{2}+33.18C^{2}\end{split}  \tag{3}\]  
Based on the coefficients of each variable, temperature (A) had the most significant positive influence on TPC for both parts of the plant. As in many cases of phenol extraction from environmental matrices, increasing the temperature increases their solubility and thus their content in the extract [40]. Notably, the effect of temperature was more critical in the case of the aboveground part than the roots. The same applied for the extraction time (B), although overall its influence was less significant than temperature. Regarding the water/plant ratio (C), a strong negative dependence was determined, indicating that as the ratio increased, the TPC decreased. This negative dependence may be attributed to either the dilution of phenols as more components from other chemical classes were extracted (such as terpen, aldehydes, and ketones) or the degradation of phenols in water-participating side-reactions. Taking into consideration the minimal influence of the water/plant ratio on the yield of the total extractables (Table 2, \(p\)-values of 0.06 and 0.17 for the aboveground part and roots, respectively), and the related published literature, the second hypothesis appears to be more realistic [41]. The ANOVA results are shown In Table 3. The regression coefficients of 98.99 and 99.27% for the aboveground part and roots, respectively, establish the applicability of the proposed model equations. With respect to the significance of each variable, the linear terms for temperature and water/plant ratio were statistically significant (\(p\) < 0.05) and played an important role in the TPC for both parts of \(O\). _mutabilis_. Contrary to these, the influence of the extraction time was deemed as insignificant for both the aboveground part and roots (\(p\)-values of 0.16 and 0.52, respectively). The CV values of 12.68 and 8.54% for the aboveground part and roots, respectively, indicate a reproducible model. \begin{table}
\begin{tabular}{c c c c c c} \hline
**TPC (Aboveground)** & **Sum of Squares** & **df** & **Mean Square** & **\(F\)-Value** & **\(p\)-Value** \\ \hline Model & 41,856.44 & 9 & 4650.72 & 54.20 & 0.0002 \\ \hline A—temperature & 2879.53 & 1 & 2879.53 & 33.56 & 0.0022 \\ \hline B—extraction time & 233.04 & 1 & 233.04 & 2.72 & 0.1603 \\ \hline C—water/plant ratio & 27,796.69 & 1 & 27,796.69 & 323.94 & \textless{}0.0001 \\ \hline \end{tabular}
\end{table} 
Table 3: Variance analysis for the total phenol contents of the aboveground part and roots of \(O\). _mutabilis_. The 3D plots of Figure 2 present the interactive effect of the variables on the TPC. Figure 2a shows the effect of extraction time and temperature on the TPC. The significant and insignificant roles of temperature and extraction time, respectively, were further established. At each and all temperatures, increasing the extraction time resulted in an approximately -5% raise in TPC. On the other hand, at each and all extraction times, doubling the temperature from 100 to 200 \({}^{\circ}\)C more than doubled the TPC (from 25-30 to 60-65%). Physical properties such as the dielectric constant of water, which decreases with increasing temperature, influences the SWE of nonpolar phenolics [42]. Nonpolar solutes become more soluble as temperature rises. These findings were in accordance with earlier results on the total phenolic content of subcritical water extracts [43; 44].