## 3 Results and Discussion
### Selection of the Molar Ratio of the NaDES Components  
A study on the effects of the molar ratios of the components acting as HBAs and HBDs of ChCl:EG and ChCl:LA on NEP extraction from mangosteen peel using UAE was carried out. Three different ratios were employed: 1:1, 1:2, and 1:3 (HBA:HBD) for the synthesis of NaDES. However, ChCl:EG (1:1) solvent could not be synthesized because at the 1:1 (HBA:HBD) molar ratio, it crystallized once it was cooled. Table 3 shows the results of total antioxidant capacity (ABTS and hydroxyl radical assays) as well as total PA content (DMAC and butanol/HCl methods) for the extracts obtained by UAE from the extraction residue of mangosteen peel using these two NaDES at different molar ratios. Regarding ChCl:LA, the extracts obtained with a 1:2 molar ratio presented the highest antioxidant capacity concerning the scavenging of ABTS radicals. However, the capacity to inhibit the formation of hydroxyl radicals was similar among molar ratios (no statistical differences were observed (\(p>0.05\))). On the other hand, with respect to ChCl:EG, the extracts attained with the 1:2 molar ratio presented greater antioxidant capacity (65% scavenging of ABTS radicals and 39% inhibition of hydroxyl radical formation) than the extracts corresponding to a 1:3 molar ratio. Nevertheless, the extracts presenting the highest PA content were those obtained with a ChCl:LA 1:2 molar ratio in DMAC and butanol/HCl assays (25.4 and 2447 mg epicatechin/100 g of sample, respectively). However, results using a butanol/HCl assay exhibited no significant differences (\(p>0.05\)) with 1:3 ChCl:LA and 1:3 ChCl:EG. To sum up, the extracts obtained with ChCl:EG (1:2 and 1:3 molar ratios) had higher antioxidant capacity than those corresponding to ChCl:LA (1:2 and 1:3 molar ratios) (Table 3). Moreover, the extracts obtained with ChCl:LA (1:2) presented the highest total PA content. Therefore, ChCl:LA with a 1:2 molar ratio, which exhibited the highest PA content and a high total antioxidant capacity, was chosen to perform the optimization of NEP extraction from the extraction residue of mangosteeen peel (Table 3). Optimization of the NaDES-UAE Extraction Parameters for NEPs from Mangosteeen Peel Extraction Residue  
Once the NaDES (ChCl:LA) and the molar ratio between components (1:2) were selected to release NEPs from the extraction residue of mangosteeen peel, a Box-Behnken experimental design was employed to optimize the percentage of water, the ultrasound amplitude, and the extraction time on five response variables for evaluating the total PA content (DMAC and butanol/HCl assays) and total antioxidant capacities (capacity to inhibit the formation of hydroxyl radicals, capacity to scavenge free radicals, and ferric-reducing antioxidant power (FRAP) methods). The values explored for these variables were set up based on the information found in the literature as well as the instrumentation and sample limitations. For instance, to reduce solvent viscosity, water was added in a range from 10 to 30% (\(\
u/\
u\)) due to higher water concentrations that might have restricted the interactions between NaDES and phenolic compounds by affecting hydrogen-bonded interactions [57; 58]. As can be seen in Table S1, by experimental design, the established 15 experiments were conducted in a randomized order, with three replicated at the central point. In addition, Table S1 presents the total PA content and total antioxidant capacity of the extracts attained in the 15 experiments. Table S2 compiles the results of the adequacy of the model as well as the analysis of variance, goodness of fit, and the coefficients of the established multiple linear regression. The regression models enabled prediction of 93.6-99.3% of the variability of the results obtained by DMAC, butanol/HCl, ABTS scavenging capacity, capacity to inhibit the formation of hydroxyl radical, and FRAP assays. These values indicated that the applied model was suitable.