## 3 Materials and Methods
### Sample Preparation and Extraction Procedures  
The collected plants were air-dried in the shade at room temperature (25 \({}^{\circ}\)C) for three weeks. Then the aboveground part (stem and leaves) and the roots were separated and reduced to powder separately with a blender (8011 ES Model HGB2 WTS3 400 W), before storing them in glass bottles at room temperature. Two extraction methods were applied: SWE and hot water maceration. SWE was carried out at laboratory scale in a Teflon-coated, homemade stainless steel reactor (150 mL capacity) fitted with a magnetic stirrer. The pressure inside the reactor was built with N\({}_{2}\) gas and fixed at 30 bar to keep the water in liquid state. The stirring speed was set at 400 rpm. The extracts obtained after extraction were vacuum-filtered through Whatman No.1 filter paper and the filtrates were stored in glass vials at 4 \({}^{\circ}\)C for further analysis.  
The method of maceration with hot water has been established as a conventional extraction method for plant tissues (extraction time 180 min, extraction temperature \(\sim\)100 \({}^{\circ}\)C) [54]. The parameters of the SWE method were optimized as described in Section 3.3. The extraction yield for both SWE and maceration was calculated as follows:  
\[\begin{array}{l}extraction\ yield\ (\%)\\ \ \ \ \ \ \  
4000 and 450 cm\({}^{-1}\) using a JASCO FTIR-ATR spectrophotometer. The volatile phenolic compounds in the extracts were analyzed using a 7890 Agilent gas chromatograph and a 7010B MS detector equipped with a DB-WAX (60 m length 0.25 mm i.d. 0.5 m thickness) capillary column. Briefly, 3 mL of extracts were put into a 20 mL headspace vial and equilibrated at 60 \({}^{\circ}\)C for 15 min. The volatiles were then extracted for 30 min by a 1 cm solid-phase microextraction fiber assembly (CAR/PDMS/DVB-fiber (Supelco), 50/30 \(\upmu\)m) with continuous stirring at 60 \({}^{\circ}\)C (250 rpm). Thermal desorption was carried out for 5 min at 250 \({}^{\circ}\)C. The column temperature was initially held at 40 \({}^{\circ}\)C for 4 min, then raised to 90 \({}^{\circ}\)C at a rate of 3 \({}^{\circ}\)C/min, then to 130 \({}^{\circ}\)C at a rate of 4 \({}^{\circ}\)C/min and held for 4 min, then raised to 240 \({}^{\circ}\)C at a rate of 5 \({}^{\circ}\)C/min and held there for 8 min. The NIST 14 library was used to identify the volatile substances in the extracts.  
The quantification of selected phenolic compounds (gallic acid, pyrocatech, catechin, caffeic acid, epicatechin, \(p\)-coumaric acid, ferulic acid, and quercetin) of the extracts were determined by using high performance liquid chromatograph coupled with diode array detector at a wavelength of 278 nm (HPLC-DAD, Shimadzu Nexera 2). The column was Inertsil ODS-4 C\({}_{18}\) (250 mm \(\times\) 4.6 mm, 5 \(\upmu\)m). The mobile phase consisted of 0.2% acetic acid in water (A) and methanol (B) using a gradient elution as follows: 0-0.1 min, 5% B; 0.1-3 min, 95% B; 3-18 min, 20% B; 18-20 min, 20% B; 20-30 min, 40% B; 30-40 min, 50% B; 40-50 min, 100% B; and 50-55 min, 5% B for equilibration of the column. The column temperature was maintained at 30 \({}^{\circ}\)C. In total, 20 \(\upmu\)L of extract were injected into the column in each run. The flow rate was 1 mL/min [58]. Analytes in each subcritical water extract were identified by comparing their retention times and UV-vis spectra with those of standard compounds. Individual stock solutions of standard phenolic compounds were prepared in methanol (2000 mg/L), and their mixtures to plot the calibration curves ranging from 0.5 to 100 mg/L were made in methanol-water (50:50, \(v/v\)). The phenolics were quantified using an external standard calibration. Limit of detection (LOD), limit of quantification (LOQ, mg/L), and the coefficient of correlation (R\({}^{2}\)) are shown in Table 5. Results were means of triplicate injections and expressed as \(\upmu\)g/100 g dry sample.