## 3 Results
### SFE Screening Experiments
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Run**} & \multicolumn{4}{c}{**Conditions**} & \multirow{2}{*}{**Phenolic Acid**} & **Concent** & **Individual** & **Total Phenolic** \\  & & **T (\({}^{\circ}\)C)** & **P (bar)** & **MeOH (\%)** & **qCO\({}_{2}\) (g/min)** & & **(mg/g)** & **Recovery (\%)** & **Recovery (\%)** \\ \hline
**E1** & 45 & 150 & 7.0 & 5.0 & Caffeic & 0.031 & 3.0 \({}^{\text{al}}\) & 0.5 \({}^{\text{a}}\) \\ \hline
**E2** & 60 & 350 & 7.0 & 5.0 & Caffeic & 0.041 & 4.0 \({}^{\text{al}}\) & 0.7 \({}^{\text{a}}\) \\ \hline
**E3** & 80 & 350 & 7.0 & 10.0 &
\begin{tabular}{c} Caffeic \\ Isochlorogenic A \\ \end{tabular} & 0.184 & 19.4 \({}^{\text{bl}}\) & \\ \hline
**E4** & 80 & 350 & 15.0 & 10.0 &
\begin{tabular}{c} Caffeic \\ Isochlorogenic A \\ \end{tabular} & 0.474 & 51.6 \({}^{\text{cl}}\) & \\ \hline
**E5** & 80 & 350 & 15.0 & 15.0 &
\begin{tabular}{c} Caffeic \\ Isochlorogenic A \\ \end{tabular} & 0.202 & 96.1 \({}^{\text{bl}}\) & 11.1 \({}^{\text{c}}\) \\ \hline \hline \end{tabular}  
* Concerning the individual recovery column, identical superscript letters indicate no significant difference among the extraction runs in relation to the respective phenolic acid (\({}^{\text{l}}\): Caffeic acid, \({}^{\text{a}}\): Isochlorogenic acid A). Similarly, in the total phenolic recovery column, identical superscript letters indicate no significant difference among the extraction runs.  
\end{table} 
Table 3: Phenolic acid supercritical fluid extraction from potato peels in screening runs. The extraction time was fixed at 60 min in all runs. convective mass transfer from the solid phase to the solvent phase. As a result, the recovery of 88% of the total isochlorogenic acid (ICA) content could be observed. Again, very high temperatures can lead to the degradation of heat sensible compounds, and 80 \({}^{\circ}\)C is at the upper limit of the temperature ranges usually reported in the literature for the extraction of peels. Therefore, in E4, only _MeOH\({}^{\circ}\)_% was changed. CO\({}_{2}\) is a nonpolar solvent and to achieve the extraction of polar compounds, as is the case with phenolics, its polarity must be increased by a cosolvent [38]. Additionally, higher amounts of cosolvent aid the dissolution of heavier molecules on the fluid phase. As a result, the same phenolics recovered in the previous runs were also extracted in E4, but in considerably higher concentrations. In E5, \(q_{CO2}\) was increased and, although TPR also increased due to the improved extraction of ISA and the first recovery of p-coumaric acid (PCA), the extraction of CFA experiences a significant decrease. This is likely to have happened because higher flow rates result in lower solvent residence times, i.e., the CO\({}_{2}\) does not remain in the extraction vessel for a period of time long enough to interact with the phenolic molecules and hence, compound affinity starts to play a major role in the extraction profile. It is very likely that continuing to increase \(q_{CO2}\) would further lower TPR values. One noteworthy fact is that even though chlorogenic acid (CGA) is the most abundant phenolic acid in potato peels, only traces were recovered in all the runs performed. Possible reasons for why this is the case are explored in detail in the next section. Finally, it is clear that increasing _MeOH_% and \(q_{CO2}\) seems to affect yields more than increasing \(T\) and \(P\). This can be observed by comparing the results of E3-E5 to those of E1 and E2. Thus being, in order to find the optimal extraction conditions for maximizing the TPR of the SFE extraction, an experimental design varying the two most influential parameters was carried out. This is shown in the next section.