## 3 Results
### Extraction of Phenolics by SFE vs. Other Techniques  
Literature data usually points to the fact that the recovery of phenolic acids by other novel extraction technologies, such as microwave-assisted (MAE), enzyme-assisted (EAE), ultrasound-assisted (UAE), subcritical-water (SWE), and pressurized-liquid (PLE) extractions, among others, tend to be more efficient than their recovery by SFE. In very recent reviews, [PERSON] [43] and [PERSON] et al. [32] compare the efficiency of some of these technologies for extracting phenolic compounds from a wide variety of matrices and confirm that, among the techniques assessed (MAE, PLE, UAE, and SFE), SFE shows the lowest yields and the highest extraction times overall. This trend is also confirmed by other research articles [35, 56]. In older articles, and even in some of the more recent studies, the results regarding phenolic concentrations and/or recoveries via different methods are shown as TPC (total phenolic content) of gallic acid equivalents, measured by the Folin-Ciocalteu method. Some of these works also include information regarding the antioxidant activity (AA) of the extracts, measured via the DPPH method. The issue with this approach is that, since individual phenolics were not identified by more reliable techniques, such as HPLC, the results of TPC and AA could potentially be affected by widely known interferents in the extracts, such as reducing sugars, acids, and/or other antioxidant compounds [57, 58]. Another related challenge is the disparity in the presentation of results across works from the literature. Some authors report extract yields as mass of phenolics (either in TPC or GAE) per dry matrix, others per mass of extract, volume of extract, and some even do so in wet basis. A more efficient way to present the results would be as % of recovery of individual and total phenolics in the extracts (relative to the raw samples), as this would enable a direct contrast between different processes and extraction protocols. Therefore, a thorough literature comparison with the results from this work is challenging. Despite the aforementioned limitations, an in-depth analysis of the literature data still allows for interesting conclusions. Table 7 presents the articles from the last decade that aimed at extracting phenolics from the peels of potato as well as of a few other vegetablesby different technologies, along with the process conditions, the phenolics identified, and the yields/recoveries attained. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Matrix** & **Extraction Technique** & **Optimal Conditions** & **Phenolic Characterization** & **Optimized Yield (Y,** **m/g Extract) or** & **\% AA** & **Ref. ** \\ \hline \multirow{8}{*}{Conventional solvent} & \multirow{3}{*}{ \begin{tabular}{c} Conventional solvent \\ 3\% acetic acid. T: 40 \%C. \\ \end{tabular}  } & Water + ethanol, C\({}_{\text{coh}}\): 59\%, & n.r. & Y: 9.11 mg CFA/g & n.r. & [59] \\ \cline{3-6}  & & Water + ethanol, C\({}_{\text{coh}}\): 59\%, & n.r. & Y: 9.11 mg CFA/g & n.r. & [59] \\ \cline{3-6}  & & R\({}_{\text{L/S}}\): 84 mL/g: T: 77 \%C & & & & \\ \cline{3-6}  & & 46\% water + 51\% ethanol + & & & & \\ \cline{3-6}  & & 3\% acetic acid. T: 40 \%C. & CGA, NCA, CFA & Y: 1.03 mg TPC/g (wet basis); R: 89-97\% & n.r. & [55] \\ \cline{3-6}  & & & & & \\  
The extraction of phenolics from potato peels has been assessed via a number of novel technologies, with satisfactory results being reported overall. Regarding the individual phenolics identified, it is interesting to notice the different profiles of phenolic acids in the structures of potato peels. The main compounds identified in the extracts are chlorogenic, caffeic, ferulic, gallic, sinapic, vannilic, syrginic, isochlorogenic, protocatechuric, and p-coumaric acids. As previously mentioned, because the results of potato peel extractions are reported in different formats and units, a direct comparison is difficult, but there are still some key points to be made.