## 3 Results and Discussion
### VOCs of Green Coffee Beans
High contents of pyrazines, pyridines, and pyrroles indicate a decrease in the quality of green coffee. In the group of aldehydes, butanal was the only VOC detected in high-quality coffee (1.28%), while nonanal and 4-hydroxy-3-methoxybenzaldehyde appeared in higher proportions in the medium- and high-quality samples. There were also several compounds that are associated with low-quality coffee, such as 2-octanal, (E)-2-nonenal, and (E,E)-2,4-nonadenal, that appeared exclusively in these samples, and they are associated with buttery fragrances. Hexanal (3.52%) and benzaldehyde (0.65%) were aldehydes found in a higher proportion, and these are markers of poor quality, a rancid odor, and/or oxidative processes [5; 9]. The VOCs of the ketone family were found exclusively in the high-quality coffee; specifically, propenone, 1-(4-nitrophenyl)-3-phenylamino (2.73%), and 3-methyl-2-cyclopent-1-one (1.02%). Both VOCs are associated with sweet smells [4; 9]. This family is usually found in coffee of the highest quality. The esters family is linked to positive fruity aromas, mainly due to 3-methylheptyl acetate, propanoic acid, 2-methyl- and octyl ester that appeared in high-quality samples but not in medium- and low-quality ones [4]. The acid derivatives such as 2-methyl-butanoic acid and 3-methyl-2-butenoic acid emit unpleasant odors [32] and only appeared in a greater proportion in the low-quality samples. Regarding the carboxylic acids, nonanoic acid and octanoic acid increased significantly in the low-quality samples. The literature links this family to pungent and rancid odors [32]. \(\gamma\)-Butyrolactone is the only compound within the lactone family that was detected in green coffee beans. Furthermore, it only appeared in the low-quality samples. The literature associates lactones with coffee quality [26] because its odor is linked to a defective odor in seeds [9]. 2-Methoxy-4-vinylphenol and benzene are the main VOCs within the aromatics family, which have a spicy clove odor. The main VOC in the alcohols groups was phenylethyl alcohol, which was the most abundant in green \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**R.T. (Min)** & **CAS Number** & **Volatile Compounds** & \multicolumn{2}{c}{**Quantities**} \\  & & **High** & **Medium** & **Low** \\ \hline \multicolumn{5}{c}{**Hydrocarbons**} \\
18.6 & 78-70-6 & 3,7-Dimethyl-1,6-octadien-3-ol (Linalool) & 0.73  a & 0.65  a & 0.36  b \\
23.6 & 124-11-8 & 1-Nemene & 0.00  & 0.00 & 0.90 \\
25.7 & 112-40-3 & Dodecane & 0.00  & 0.00 & 0.53 \\
41.4 & 629-59-4 & Tetradecane & 0.85  c & 3.55  a & 3.35  b \\  & & **Sulfur compounds** & & \\
1.9 & 75-18-3 & Dimethyl sulfide & 0.00 & 1.98  & 5.48  \\
**Thiophenes** & & & & \\
16.8 & 2557-78-0 & o-Fluorothiophenal & 2.88  & 2.99 & 0.00 \\
25.2 & 1708-32-3 & 2,5-Dihydro-thiophene & 0.33  c & 1.67  & 2.79  \\  & & **Others** & & \\
8.1 & 100-42-5 & Styrene & 1.01  & 0.52  & 0.14  c \\
11.6 & 127-91-3 & Beta-Pinene & 1.67  & 0.00 & 0.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._coffee and has a floral smell [33]. Tetradecane, 1-nonene and dodecane, which smell of solvent [4], were the VOCs that appeared in the majority of the hydrocarbons group. These negative attributes only appeared in the low-quality group. Dimethyl sulfide was the only VOC detected in the sulfur compounds family in the low-quality samples. This compound has a putrid or decomposing odor [34]. Finally, in other groups, we must highlight that styrene and beta-pinene presented aromas linked to fresh fruit, citrus, herbs, and green onions [17].