# Characterization of Coffee Silver Skin as Potential Food-Safe Ingredient
## 3 Results
### Volatile Organic Compounds (VOCs) in CSS  
Volatile organic compounds (VOCs) in CSS, from this study, were grouped into seven classes (Table 5). The order of concentrations is nitrogen-containing compounds, pyrazines, aldehydes, alcohols, other compounds, hydrocarbons, and ketones. In coffee, many volatiles come from the roasting process of beans. Although there are few studies about VOCs from CSS, the typical volatiles found in coffee beans can be assumed for CSS.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**VOCs from CSS** & **Area \%** \\ \hline Aldehydes & \\ \hline
3-Furaldehyde & 1.32 \\ Benzaldehyde & 2.51 \\ Butanal, 2-methyl- & 2.95 \\ Butanal, 3-methyl- & 3.19 \\ Heptanal & 1.51 \\ Hexanal & 8.83 \\ Pentanal & 0.81 \\ Propanal, 2-methyl- & 2.20 \\ \hline Alcohols & \\ \hline
1-Methylcyclopropenemethanol & 3.00 \\
1,3-Butanediol, (S)- & 1.26 \\
2-Furanmethanol & 0.47 \\
2-Furanmethanol, acetate & 0.47 \\
2-Nonen-1-ol & 7.51 \\
2-Octen-1-ol, (E)- & 0.23 \\
2-Octyn-1-ol & 0.34 \\
3-Hexen-1-ol, 2-ethyl- & 0.43 \\ \hline Ketones & \\ \hline
2-Propanone, 1-(acetyloxy)- & 1.11 \\ \hline Nitrogen-containing species & \\ \hline (2-Aziridinylethyl)amine & 1.30 \\
3-Amino-2-oxazoldinone & 1.98 \\ Carane, 4,5-epoxy-, trans & 1.58 \\ Hydroxyurea & 0.72 \\ O-Methyllisourea & 0.43 \\ Propanamide, 2-hydroxy- & 0.32 \\ \hline Pyrazines & \\ \hline
1-Methyl-3-Phenylpiperazine & 0.69 \\ Pyrazine, methyl- & 4.38 \\ Pyrazine, 2-ethyl-6-methyl- & 2.40 \\ Pyrazine, 2-ethyl-3-methyl- & 6.65 \\ Pyrazine, 3-ethyl-2,5-dimethyl- & 1.75 \\ Pyrazole, 3,5-dimethyl-1-allyl- & 0.78 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Qualitative profile (area %) of main volatile compounds (VOCs) from CSS.  
Recently, for the first time, [PERSON] et al. [66] researched the volatiles of CSS. By HS-SPME-GC-MS, they found more than 80 active odorants, with many of them shown in the data reported here. Furthermore, by GC-O/FID and GC \(\times\) GC-TOF analysis and comparison with coffee beans, they were able to identify some characteristic compounds, such as 1-octen-3-one, 2-phenylethanol, and \(\gamma\)-decalactone, not seen in this study.  
Classes of compounds found here are also reported in other studies [67; 68; 69], although is very difficult to compare different samples because of the roasting parameters, provenience of coffee beans, their composition (also including the number of defective ones), the blending of cultivars chosen, and the selected processing method (wet vs. dry) [68]. [PERSON] et al. [69] showed how the increase or decrease in thirty-seven typical compounds occurred during the roasting process, highly influencing the quality of the final coffee beans and used as quality markers. Specifically, five defects were found (light, scorched, dark, baked, and underdeveloped) and connected to elevated levels of indole, 4-ethyl-2-methoxy phenol, phenol, maltol, and 2,5-dimethylfuran, respectively. Besides these difficulties, [PERSON] and co-workers [70] listed fifteen \"iconic\" compounds which influence the coffee aroma. Among them, butanal, 2-methyl-butanol, 3-methyl-pyrazine, 2-ethyl-6-methyl-, pyrazine, and 3-ethyl-2,5-dimethyl were also present in CSS samples from this study (Table 5). A study on pyrolysis products (bio-oil) of coffee silver skin coupled with a two-dimensional (GC \(\times\) GC/qMS) analysis [71] showed a great variety and complexity of compounds, as follows: N-compounds, phenols, unsaturated aliphatic hydrocarbons (8.28%), saturated hydrocarbons, aromatic hydrocarbons, ketones, esters, carboxylic acids, alcohols, and 10 compounds classified as \"other\". Pyrolysis allowed the authors to list the most abundant active compounds, find typical regions of elution, understand the compounds' provenience (i.e., phenols, coming from the degradation of lignin), and to adjust the pyrolysis conditions.