## 3 Results
### Phenolic Identification and Quantification  
Table 2 shows the phenolic acid results in potato peels, both as TPC (mg GAE/g, via the Folin-Ciocateu method) and as concentration of individual phenolics (mg/g).  
According to the literature, the main phenolic acid in potato peels is chlorogenic acid, which can constitute up to 90% of the TPC [27]. Other phenolic acids reported in potato peels, but not present in our samples, include crypto-chlorogenic, ferulic, gallic, and protocatechuric acids [5; 6]. Some of these may be present in this matrix in esterified (conjugated to small peptides or oligosaccharides) or in bound form, i.e., covalently attached to cell wall components, such as cellulose, hemicellulose, lignin, pectin or structural proteins [13; 28].  
As expected, chlorogenic acid was the most abundant phenolic in our samples (3.87 mg/g), comprising around 64% of the TPC, followed by caffe acid (0.92 mg/g, 15% of the TPC). These two major phenolics make up around 80% of the total phenolic content, and it is clear that extraction protocols should focus primarily on their recovery. Similar concentrations and ratios for these phenolics are reported in other works from the literature [14; 17; 27]. Additionally, the literature reports lower phenolic contents for samples of potato flesh: 0.17-2.83 mg/g chlorogenic acid and 0.25-0.72 mg/g caffe acid [4]. The TPC differences observed between both matrices can be explained by the fact that the concentration of the phenolic acids is always higher in the peels than in the flesh [29]. This is because, in vegetables, these secondary metabolites play a key role in many physiological reactions, such as pigmentation, growth, reproduction, and protection [30]. Therefore, because it acts as a natural barrier between the flesh and the external environment, vegetable peels tend to contain a higher phenolic content, as they can provide good resistance against mechanical stresses and pathogens [31].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Compound (\%, _vel/w_)** & **Potato Peels** & **Potato Flesh** \\ \hline
**Moisture** & 6.6 \(\pm\) 0.4 a & 7.2 \(\pm\) 0.4 a \\
**Protein** & 11.0 \(\pm\) 0.15 a & 7.1 \(\pm\) 0.21 b \\
**Lipids** & 1.75 \(\pm\) 0.02 a & 2.61 \(\pm\) 0.05 b \\
**Total carbohydrates,** & 62.4 \(\pm\) 3.3 a & 76.4 \(\pm\) 3.3 b \\
**of which:** & 20.0 \(\pm\) 1.3 & 47.7 \(\pm\) 2.8 \\
**Cellulose** & 32.4 \(\pm\) 0.7 & 28.7 \(\pm\) 0.5 \\
**Hemicululose,** & 10.0 \(\pm\) 0.7 & 0 \\ \hline
**Galacturonic acid** & 2.64 \(\pm\) 0.21 & n.d. \\
**Galactose** & 6.34 \(\pm\) 0.33 & n.d. \\
**Arabinose** & 1.01 \(\pm\) 0.09 & n.d. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Macronutrient composition of potato peels and flesh in d.b. (dry basis).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Phenolic Acid** & **Concentration (mg/g)** &
\begin{tabular}{c} **Total Phenolic Content** \\ **(mg GAE/g)** \\ \end{tabular} \\ \hline
**Chlorogenic acid** & 3.87 & \\
**Caffeic acid** & 0.92 & \\
**Neochlorogenic acid** & 0.44 & \\
**Isochlorogenic acid B** & 0.33 & 5.24 \\
**Vanillic acid** & 0.31 & \\
**Isochlorogenic acid A** & 0.21 & \\
**_p-_**cumaric acid** & Trace & \\
**Salicylic acid** & Trace & \\ \hline
**Total** & **6.08** & **5.24** \\ \hline \hline \end{tabular}
\end{table}
Table 2: Identification and quantification of phenolics in the samples of potato peels.