## 4 Discussion  
### Influence of PLE Temperature on the Recovery of Phenolic Compounds from Burdock Roots  
The extraction of phenolic compounds from various natural matrices using PLE has been extensively studied [33; 38; 39; 40; 43]. In this context, several researchers have utilized the optimized PLE conditions established by [PERSON] et al. [43], which involve the use of EtOH/H\({}_{2}\)O solvent mixture (70:30, \(v/v\)) for 20 min at 1500 psi [33; 38; 39; 40]. These conditions were applied to extract phenolic compounds from burdock roots. The extraction temperature is a critical parameter influencing the recovery of phenolic compounds. Depending on the matrix composition, elevated temperatures may induce undesired chemical reactions or lead to the degradation of thermolabile compounds, ultimately diminishing the bioactive potential of the extracts [33]. Phenolic compounds in burdock, including chlorogenic acid, are known to be particularly sensitive to thermal degradation [44]. In fact, [PERSON] et al. [33] observed that PLE temperatures higher than 100 \({}^{\circ}\)C result in the degradation of several phenolic compounds from burdock roots, including chlorogenic acid, when 2-MTHF is used as an extraction solvent. However, the type of solvent used can influence the optimal extraction temperature, as solvents differ in their polarity, hydrogen-bonding capacity, and thermal stability, which can affect not only the solubility of phenolic compounds, but also their susceptibility to thermal degradation. Certain solvents can create a more protective microenvironment by stabilizing phenolic structures through solvent-solute interactions, thereby reducing oxidation or decomposition during high-temperature extraction processes. Considering that the EtOH/H\({}_{2}\)O mixture (70:30) is the most commonly used solvent system for extracting phenolic compounds from natural matrices, it is essential to understand how extraction temperature affects the stability, recovery, and overall profile of phenolic compounds when using this solvent. Temperature variations can influence the solubility and diffusion of phenolics, but may also promote their degradation or transformation, which underscores the importance of optimizing thermal conditions for this widely applied solvent mixture. The results revealed that, while PLE at 150 \({}^{\circ}\)C resulted in the highest yields, this extract exhibited the lowest TPC when compared to extracts obtained at 50 \({}^{\circ}\)C and 100 \({}^{\circ}\)C, as well as the SLE extracts (see Table 1). This decrease in TPC at higher temperatures could be attributed to the thermal degradation of polyphenols. It is well-documented that SLE at temperatures above 80 \({}^{\circ}\)C can lead to polyphenol degradation, while PLE has been shown to resist such degradation at higher temperatures, ranging from 150 \({}^{\circ}\)C to 200 \({}^{\circ}\)C [45]. Additionally, the OLE extract obtained at 150 \({}^{\circ}\)C appeared darker and emitted a stronger aroma compared to extracts obtained at lower temperatures, which is likely due to the formation of Maillard reaction products, a well-known phenomenon in thermally treated samples [46; 47]. Furthermore, the OLE PLE extract obtained at 100 \({}^{\circ}\)C exhibited lower total phenolic content (TPC) compared to the extract obtained at 50 \({}^{\circ}\)C in this study. This effect was also observed by [PERSON] et al. [33] when using PLE temperatures higher than 100 \({}^{\circ}\)C, achieving dark burdock root extracts using 2-MTHF as solvent. This observation underscores the high thermosensitivity of the polyphenols in burdock roots, but also that this sensitivity depends on the extraction solvent employed [33]. It is probable that the degradation of phenolic compounds from burdock roots during PLE at temperatures above 50 \({}^{\circ}\)C with EtOH/H\({}_{2}\)O is mainly due to the high polarity and reactivity of the solvent mixture, which can promote oxidation, hydrolysis, and thermal breakdown [33; 41; 43].