## 3 Results and Discussion
### Effect of Sample Preparation Variables on Hydroxycinnamic Acid Recoveries  
According to the ANOVA results, the solvent-to-sample ratio was the most dominant factor, negatively influencing hydroxycinnamic acid responses in its linear form (C) and positively affecting them in its quadratic term (C\({}^{2}\)). With an increase in solvent-to-sample ratio from 10 to 25 mL g\({}^{-1}\), the hydroxycinnamic acids contents gradually decreased. With a further increase in the solvent-to-sample ratio, its positive quadratic effect dominates, and, thus, a slight increase in the responses was observed. The solubilization efficiency probably decreased due to the uneven distribution of the cavitation phenomenon resulting from the over dilution effect [28]. Thus, using lower volumes of solvent may enhance polyphenol solubilization, prevent unnecessary wastage of solvents, and reduce the cost of the process. Ethanol concentration, in its linear form, demonstrated a weaker but still significant effect on caffe acid and chlorogenic acid responses. The increase in ethanol concentration resulted in a decrease in chlorogenic acid content. An optimal solvent composition exists at the lower ethanol concentration range. The results may be related to the solvent polarity and the solubility preference of hydroxycinnamic acids. As water content in the aqueous  
Figure 1: Comparison between experimental data (actual) and calculated from the model values (predicted). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Term**} & \multicolumn{2}{c}{**Caffeic Acid**} & \multicolumn{2}{c}{**Chlorogenic Acid**} & \multicolumn{2}{c}{**Ferulic Acid**} \\  & **F-Value** & **_p-Value_ & **F-Value** & **_p-Value_ & **F-Value** & **_p-Value_ \\ \hline Model & 95.57 & \textless{}0.0001 & 108.57 & \textless{}0.0001 & 89.46 & \textless{}0.0001 \\ A & 28.10 & 0.0001 & 5.97 & 0.0231 & - & - \\ B & 3.11 & 0.0939 & 4.97 & 0.0363 & 4.99 & 0.0351 \\ C & 671.19 & \textless{}0.0001 & 559.43 & \textless{}0.0001 & 306.70 & \textless{}0.0001 \\ D & 2.45 & 0.1340 & - & - & - & - \\ AB & 5.62 & 0.0285 & - & - & - & - \\ AC & - & - & - & - & - & - \\ AD & - & - & 4.80 & 0.0394 & 5.86 & 0.0234 \\ BC & - & - & - & - & - & - \\ BD & 11.09 & 0.0035 & - & - & - & - \\ CD & - & - & - & - & - & - \\ A\({}^{2}\) & - & - & - & - & - & - \\ B\({}^{2}\) & 9.12 & 0.0070 & 4.80 & 0.0394 & - & - \\ C\({}^{2}\) & 91.30 & \textless{}0.0001 & 64.99 & \textless{}0.0001 & 40.28 & \textless{}0.0001 \\ D\({}^{2}\) & 16.82 & 0.0006 & 2.31 & 0.1509 & - & - \\ Lack of fit & 1.26 & 0.4514 & 3.56 & 0.1133 & 2.95 & 0.1513 \\ R\({}^{2}\) & 0.9784 & & 0.9673 & & 0.9371 \\ R\({}^{2}\)\({}_{\text{adj}}\) & 0.9682 & & 0.9584 & & 0.9267 \\ R\({}^{2}\)\({}_{\text{pred}}\) & 0.9365 & & 0.9304 & & 0.9064 \\ Adeq Precision & 31.540 & & 32.2520 & & 30.1803 \\ C.V. (\%) & 9.10 & & 8.27 & & 9.94 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Analysis of variance (ANOVA) and descriptive statistics for the developed quadratic models. ethanolic mixture increases, solvent polarity is enhanced, thus improving the solubility of the target analytes [29]. As regards temperature in sample preparation, it significantly affected chlorogenic acid and ferulic acid contents linearly (positive effect) and caffeic and chlorogenic acid contents in a quadratic manner (negative effect). The positive linear effect of temperature can be attributed to its positive influence on the solubilization kinetics [30]. Increased solubility of polyphenols with increasing temperature was also reported in previous studies [31]. On the other side, polyphenol thermal degradation due to elevated temperatures may have resulted in the negative quadratic term of temperature for caffeic acid and chlorogenic acid responses [32]. A negative quadratic effect was observed for sonication time only in the case of caffeic acid. Prolonged sonication times increase the possibility of decomposition and/or oxidation of polyphenols, resulting in lower estimated contents.