## 3 Results and Discussion
### Selection of the Molar Ratio of the NaDES Components
Furthermore, ANOVA was used to determine the competence of the regression model and the results (see Table S2). Most of the responses presented \(p\)-values for the lack-of-fit test that were higher than 0.05, being adequate, except for the ABTS scavenging capacity assay (\(p\)-value = 0.0082) showing the suitable fitting of data to the model (see Table S2). The effects of the variables on the responses are shown as a response surface 3-D contour plot (Figure 2). According to Figure 2A,B and data grouped in Table S2, the extraction time and ultrasound amplitude were positively correlated with the extraction of PAs. In addition, the percentage of water presented a negative correlation with the total PA content measured by butanol/HCl assay, while it did not have a significant influence (\(p>\) 0.05) with the DMAC assay. On the other hand, the total antioxidant capacity of the extracts was also positively correlated with the extraction time and the ultrasound  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**NaDES** & **DMAC (mg Epicatechin/100 g Sample)** & **Butanol/HCl (mg Epicatechin/100 g Sample)** & **Hydroxyl Radical (\% of Inhibition)** & **\% Scavenging of ABTS Radicals** \\ \hline ChCl:LA & & & & \\
1:1 & 13.7 \(\pm\) 0.5 d & 1230 \(\pm\) 182 b [FOOTNOTE:b]Footnote b: \(\pm\)0.5 d: \(\pm\)0.  
amplitude, whereas the percentage of water displayed a negative correlation when the antioxidant capacity was measured by the capacity to inhibit the formation of hydroxyl radicals and the capacity to scavenge ABTS**+** assays, being also negative but not significant the influence of water percentage on the antioxidant capacity displayed by FRAP assay (Figure 2C-E). As shown in Table 4, the optimal extraction conditions to release PAs with high antioxidant capacity were a percentage of water of 18.8% (\(\
u/\
u\)), employing an ultrasound amplitude of 60% for 15 min. Table 4 displays the theoretical optimal values that should be reached under optimal UAE-NaDES conditions and the experimental results obtained under these conditions by following the methodology described in Section 2.4. The experimental values of total PA content, using the DMAC method, and antioxidant capacity, measured by the capacity to scavenge ABTS**+** and inhibit the formation of hydroxyl radicals, were within the theoretical values of the predictive model. However, the experimental values obtained regarding the total PA content exhibited by the butanol/HCl assay as well as the total antioxidant capacity showed with the FRAP assay were lower and higher, respectively, than the theoretical values (see Table 4). In general, the results obtained through confirmation experiments indicated that the predictive model from the experimental design predicted well the extraction of antioxidant NEPs by UAE, with ChClLA (1:2) as the solvent, from the extraction residue of mangosteen peel. Figure 2: 3-D contour plots showing the effects of the extraction time (min), the ultrasound amplitude (%), and the percentage of water (%) in the NaDES (ChCl:LA, 1:2) on the total PA content (DMAC (**A**) and butanol/HCl (**B**) assays) and total antioxidant capacity (ABTS scavenging capacity (**C**), capacity to inhibit the formation of hydroxyl radicals (**D**), and FRAP (**E**) assays) of extracts obtained from the extraction residue of mangosteen peel. Comparison of NEP Extraction by UAE-NaDES from the Extraction Residue of Mangosteen Peel with the Conventional Extraction of EPPs from Mangosteen Peel  
As can be observed in Table 4, the extracts collected from the extraction residue of mangosteeen peel, using the optimal UAE-NaDES extraction conditions to reach the highest content of antioxidant NEPs, were compared with the extracts obtained by the conventional extraction method of antioxidant EPPs from mangosteeen peel. The optimal UAE-NaDES extraction method obtained extracts with higher PA contents and total antioxidant capacities than the extracts obtained by the conventional extraction method.