## 3 Results and Discussion
### Extraction Process Optimization
The \(R_{L/S}\) parameter showed a high significance, which is in agreement with previous investigations that have reported the importance of proportionality between the plant material and the solvent in the extraction optimization processes [37]. This key parameter displays a major role in diffusional phenomena, which largely defines the course of extraction and yield. A high extraction yield is usually observed when a larger proportion of liquid phase is used since polyphenols are more solubilized, and a saturation concentration is achieved [38; 39]. In this work, the optimal \(R_{L/S}\) (150 mL g\({}^{-1}\)) was higher than the values reported in the literature, which usually varied between 10 and 45 mL g\({}^{-1}\) using DESs and also higher than those of conventional solvents that can reach 120 mL g\({}^{-1}\) in some investigations [40; 41]. The observed discrepancies among scientific works regarding the value of the optimum \(R_{L/S}\) could originate from the variation in the extraction solvent and the experimental conditions (temperature, stirring, time extraction, etc. ), the \(R_{L/S}\) range selected, and, most likely, the source of polyphenols. Although a common objective is to optimize the extraction of polyphenols, the different extraction conditions could affect the determination of the \(R_{L/S}\) optimum value and, consequently, the comparison herein. Similar to \(R_{L/S}\), \(C_{\text{DES}}\) showed a high significance regarding the extraction yield of polyphenols from OLLs. The optimum level of \(C_{\text{DES}}\) was the same in all three DESs in this study (90% _w/v_, Table 5) meaning that the amount of water (\(C_{\text{w}}\)) required to attain a maximum yield is the same in all cases. Water addition to DESs is one of the ways to tailor the physicochemical properties of DESs. Thus, fine-tuning the \(C_{\text{w}}\) is central to adjusting DESs properties, such as viscosity and polarity that significantly affect the yield of extraction [42]. Figure 1: _Cont._  
Recent studies have estimated the optimal \(C_{\text{w}}\) to vary from 10% to 50% [43], reaching even 63.8% by [PERSON] et al. [44]. It has been noted that water addition to DESs up to a certain point and above the optimal \(C_{\text{w}}\) could negatively affect the extraction yield since a large amount of water could cause hydrogen bonds to rupture between HBD and HBA [45]. The outcome with regard to the optimum \(C_{\text{w}}\) values was found to be 10% (\(v/v\)) for all three DESs tested. This information suggests that all three HBAs tested are equally demanding in water and the differences in the structure and the physicochemical properties of lysine, proline, and arginine did not affect the polarity of the DESs. Such an outcome was rather contradictory with published information that supported differences in \(C_{\text{w}}\) using HBAs with different chain lengths. It has been found that the longer the chain, the higher the amount of water required [46]. Hence, the basis behind the efficiency difference of the three DESs herein would be related to another reason such as the pH of the extraction medium [47]. The alkalinity offered by the amino acids provided a more or less alkaline environment to ionize polyphenols, which may turn them more polar and soluble in the solvent. Lysine, proline, and arginine have the corresponding pKa, 10.57, 10.47, and 12.10, respectively. The result expected on the basis of the claimed explanation would be the order of GL-Arg, GL-Lys, and lastly, GL-Pro in terms of solvent efficiency. However, the actual order obtained was GL-Lys, GL-Arg, and lastly, GL-Pro, which only explains the GL-Lys and GL-Pro order. This outcome suggests the existence of another important factor regarding GL-Arg.