## 2 Materials and Methods
### Chemical Characterization of Potato Samples  
In order to compare the macronutrient composition of the samples of potato flesh and peels, analyses of total protein, lipid, carbohydrate, and starch content were carried out.  
Total protein content was determined by the Kjeldahl method [19]. Briefly, 0.4 g of sample were wrapped in Whatman #1 paper and submitted to digestion with 25 mL of H\({}_{2}\)SO\({}_{4}\) (\(>\)95%, \(v/v\)) at 85 \({}^{\circ}\)C for 60-90 min, until the samples had been fully digested. The solutions were then cooled to room temperature, distilled (323 Distillation Unit, Buchi, UK), and re-suspended in water and 1.0 M NaOH. At this point, 50 mL of H\({}_{3}\)BO\({}_{3}\) was added to the final solution, which was titrated with 0.1N H\({}_{2}\)SO\({}_{4}\), with methyl red used as indicator. The amount of nitrogen and protein present (%, \(w/w\)) was calculated according to Equations (1) and (2), respectively:  
\[\%\ Nitrogen=\frac{V_{H2 SO4}(\text{mL})*\text{N}*14,007*100}{w_{sample}(mg)} \tag{1}\]  
\[\%\ Protein=\ \%\ Nitrogen*6.25 \tag{2}\]  
where \(V_{H2 SO4}\) is the volume (mL) of 0.1 N sulfuric acid consumed during titration, \(N\) is the normality of H\({}_{2}\)SO\({}_{4}\), and \(w_{sample}\) is the weight of the sample submitted to digestion.  
The lipid content was determined gravimetrically, by Soxhlet method [20]. Briefly, 1.0-2.0 g of sample were added to a cotton thimble and placed in a Soxhlet extractor, along with pre-weighted boiling flasks. Petroleum ether was used as solvent (Merck Life Science UK Limited, Dorset, UK, 60 \({}^{\circ}\)C boiling point) and extraction was carried out for 4 h. The flasks containing the fat residue were oven-dried, placed in a desiccator, and weighed. The total lipid content was calculated by weight difference.  
The total carbohydrate content was determined according to the protocol of the National Renewable Energy Laboratory (NREL) [21]. In brief, 300 mg of sample were submitted to hydrolysis with 3 mL H\({}_{2}\)SO\({}_{4}\) (\(72\%,v/v\)) and incubated at 30 \({}^{\circ}\)C for 1 h. The resulting solution was diluted with water to 3% H\({}_{2}\)SO\({}_{4}\) (\(v/v\)) and autoclaved at 121 \({}^{\circ}\)C for 30 min. Samples were allowed to cool down to room temperature, the pH of the supernatant was adjusted to 5.0 with CaCO\({}_{3}\) and filtered, and analysis in a High Pressure Liquid Chromatography (HPLC) system (Agilent Infinity, 1260 series) was performed.  
This consisted of DAD/RI detectors and an Aminex HPX-87H (300 \(\times\) 7.8 mm, Biorad, Hertfordshire, UK) column. An isocratic mobile phase of 0.005 M H\({}_{2}\)SO\({}_{4}\) was used, and the flow rate was set at 0.6 mL/min. The sample injection volume was 20 \(\mu\)L and sugar identification and quantification were attained through data comparison to previously plotted calibration curves of external standards.  
Finally, the starch analysis was performed using an enzymatic kit (Megazyme, Wicklow, Ireland), which followed the specific AOAC method [20]. The absorbance of the final samples at 510 nm was measured against a blank and a glucose standard in a UV-Vis spectrophotometer (Life Technologies Ltd., Paisley, UK).