## 3 Results and Discussion
#### 3.1.3 Impact of Different Extraction Factors on the Total Flavonoid Content (TFC)  
Based on the experimental results obtained from the fifteen trials reported in Table 2, the highest content of total flavonoid compounds (TFC) is 7.94 \(\upmu\)g QE/mg DE. This value was obtained in trial number 12 with a 1:10 g/mL solid-to-liquid ratio, an extraction temperature of 45 \({}^{\circ}\)C, and an extraction time of 30 min. However, the lowest content of total flavonoid compounds (TFC) was 2.23 \(\upmu\)g QE/mg DE, obtained in test 6 with a solid-to-liquid ratio of 1.5:10 g/mL, an extraction temperature of 40 \({}^{\circ}\)C, and an extraction time of 10 min. Furthermore, based on the ANOVA results presented in Table 3, the low level of coefficient of variance (C.V.%) and the high values of the determination coefficient (\(R^{2}\)) and adjusted determination coefficient (\(R^{2}_{(adj)}\)) derived from the total flavonoid content (TFC) model of _C. monacantha_ are 5.67, 0.9859, and 0.9605, respectively, demonstrating the relevance of this response. Likewise, the high value of the lack-of-fit probability of the total flavonoid content (TFC) model (\(p=0.4002\)) is significant at the 0.05 level (\(p>0.05\)), indicating that the experimental results have an excellent correlation with the results predicted by this model. In addition, the data provided by the ANOVA analysis and summarized in Table 3 indicate the different effects of the three independent variables, including linear effects (of extraction temperature (\(X_{j}\)) and extraction time (\(X_{k}\))) and interaction effects (of temperature-extraction time (\(X_{jk}\)) and the ratio of solid-to-liquid-extraction time (\(X_{ik}\))), which positively and significantly influenced the total flavonoid content of _C. monacantha_ Del. In contrast, negative and significant effects were observed on the TFC response through the interaction effect of the solid-to-liquid ratio-extraction temperature (\(X_{ij}\)) and the quadratic effect of the square of the solid-to-liquid ratio (\(X_{ii}\)). The final equation for TFC response is expressed after removing the insignificant effects of factors (\(p>0.05\)) from the second-order polynomial equation for this response through Equation (7) as follows:  
\[Y_{TFC}=31.82833-1.16467X_{j}-1.097558X_{k}-3.12167X_{ii}-0.171000X_{ij}+0.088 500X_{ik}+0.029650X_{jk} \tag{7}\]  
The different three-dimensional response surfaces of total flavonoid content (TFC) presented in Figure 2 clearly explain these results. Figure 2e indicates a linear proportional correlation between the flavonoid concentration of _C. monacantha_ Del. and the extraction time, extending up to 30 min. Moreover, a similar proportional linear correlation is recorded in Figure 2f between flavonoid content (TFC) and extraction temperature up to 45 \({}^{\circ}\)C. This finding is identical to that of [PERSON] et al. [81], who extracted phenolic components from _Momordia charantia_ L. using the UAE method and found that the total flavonoid content increased when the extraction temperature increased from 30 to 60 \({}^{\circ}\)C.  
In contrast, as shown in Figure 2e,f, a quadratic correlation is observed between the total flavonoid content (TFC) of _C. monacantha_ and the solid-to-liquid ratio. When the extraction is performed for ten minutes at 40 \({}^{\circ}\)C, a significant increase in the TFC response is observed, and the solid-to-liquid ratio increases from 0.5:10 g/mL to 1.00149:10 g/mL. As the solid-to-liquid ratio exceeds 1.00149:10 g/mL, a remarkable decrease in the TFC response is observed until a minimum flavonoid content of 2.23 \(\upmu\)g QE/mg DE is observed, with a solid-to-liquid ratio of 1.5:10 g/mL. The interactive effect between solid-to-liquid ratio and extraction time of the UAE method demonstrated that a significant increase in total flavonoid content (TFC) is observed when the extraction time is extended up to 30 min, using a solid-to-liquid ratio of 1.5:10 g/mL compared to a solid-to-liquid ratio of 0.5:10 g/mL (Figure 2e).