## 3 Results
### Extraction Yield and Extraction Efficiency  
In this study, different PLE conditions were evaluated and compared in terms of yield and recovery of individual phenolic compounds from artichoke by-products. The extraction yield was expressed as weight of collected extract per dry plant material (_w/w_, in grams) used in the extraction procedure. The extraction efficiency of individual compounds was estimated by a semi-quantitative approach, measuring the peak areas of the compounds identified in the chromatogram as expressed as mean \(\pm\) standard deviation of three consecutive injections. Table 3 includes the extraction yield and phenolic extraction efficiency for the _C. scolymus_ L. PLE extracts. Concerning the extraction yield, the obtained results in the different PLE experiments are highly inconstant. Similar variations were observed in other PLE extracts from plants such as black mulberry or sweet cherry stems, ranging from 11% to 48% or from 3% to 49%, respectively [23; 25]. In general, it could be observed that the application of elevated temperatures (above 170 \({}^{\circ}\)C) resulted in higher extraction yields. Indeed, PLE 3 (200 \({}^{\circ}\)C, EtOH 50%), PLE 2 (176 \({}^{\circ}\)C, EtOH 85%), and PLE 5 (176 \({}^{\circ}\)C, EtOH 15%) were the extraction conditions with the highest yield values (57 \(\pm\) 2%, 50 \(\pm\) 1%, and 45 \(\pm\) 2%, respectively). This fact could be explained by the increase in solvent diffusivity with increasing temperature, which enhances the extraction of several components from vegetable matrices [26]. In contrast to this observation, it could not establish a relationship between the percentage of ethanol and extraction yield. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Experimental Condition** & **Dielectric Constant** & **Extraction Conditions** & **Yield** & **Total Phenolic Acids** & **Total Flavonoids** & **Total Phenolic Compounds** \\ \hline PLE 1 & 19.0 &
\begin{tabular}{c} 120 \({}^{\circ}\)C; EtOH \\ 100\% \\ \end{tabular} & 7.4 \(\pm\) 0.3 & 787 \(\pm\) 25 & 488 \(\pm\) 13 & 1274 \(\pm\) 37 \\ \hline PLE 2 & 21.6 & 176 \({}^{\circ}\)C; EtOH 85\% & 50 \(\pm\) 1 & 190 \(\pm\) 10 & 94.1 \(\pm\) 0.3 & 284 \(\pm\) 10 \\ \hline PLE 3 & 26 & 200 \({}^{\circ}\)C; EtOH 50\% & 57 \(\pm\) 2 & 285 \(\pm\) 10 & 157 \(\pm\) 1 & 442 \(\pm\) 10 \\ \hline PLE 4 & 31.0 & 63 \({}^{\circ}\)C; EtOH 85\% & 10.5 \(\pm\) 0.8 & 728 \(\pm\) 24 & 365 \(\pm\) 8 & 1092 \(\pm\) 33 \\ \hline PLE 5 & 33.4 & 176 \({}^{\circ}\)C; EtOH 15\% & 45 \(\pm\) 2 & 134 \(\pm\) 4 & 43.9 \(\pm\) 0.4 & 178 \(\pm\) 4 \\ \hline PLE 6 & 34.7 & 120 \({}^{\circ}\)C; EtOH 50\% & 40 \(\pm\) 2 & 343 \(\pm\) 5 & 145 \(\pm\) 2 & 489 \(\pm\) 4 \\ \hline PLE 7 & 48.0 & 40 \({}^{\circ}\)C; EtOH 50\% & 19 \(\pm\) 1 & 594 \(\pm\) 16 & 253 \(\pm\) 16 & 848 \(\pm\) 17 \\ \hline PLE 8 & 50.4 & 120 \({}^{\circ}\)C; EtOH 0\% & 37 \(\pm\) 2 & 302 \(\pm\) 8 & 66 \(\pm\) 1 & 368 \(\pm\) 7 \\ \hline PLE 9 & 59.1 & 63 \({}^{\circ}\)C; EtOH 15\% & 25 \(\pm\) 2 & 291 \(\pm\) 18 & 75 \(\pm\) 4 & 365 \(\pm\) 22 \\ \hline \end{tabular}
\end{table} 
Table 3: Extraction yield and phenolic compounds recovery for _C. scolymus_ L. obtained in each PLE condition. Yield (%), individual phenolic compounds (peak area \(\times\) E + 4). Value = mean \(\pm\) standard deviation. Focusing on the individual recovery of phenolic compounds of each PLE condition, a relationship between the extraction parameters (temperature and percentage of ethanol) and the enhancement extraction of particular compounds could be revealed. In this sense, regarding phenolic compounds, as described above, both sub-classes of polyphenols (phenolic acids and flavonoids) identified in the samples were extracted under all the PLE experiments. The individual areas of all compounds identified in PLE extracts were also analyzed to evaluate significant differences among the different PLE conditions.