## 3 Results and Discussion
### Volatile Composition of Single-Dose Espresso Coffee-Based Blends
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & **CAS Number** & **Reported \({}^{*}\)** & **Aroma Descriptor \({}^{\text{b}}\)** & **References \({}^{*}\)** \\ \hline
**Acids** & & & & \\ \hline \hline _Aliphatics_ & & & & \\ \hline Acetic acid & 64-19-7 & [3] & Pungent, sour, acidic, vinegar & [20; 34; 35; 36] \\ Propanoic acid & 79-09-4 & [3] & Pungent, rancid, sour milk, cheese, butter-like & [34; 35; 36] \\ Butanoic acid & 107-92-6 & [3] & Sour, rancid, butter-like, sweaty, rubbish & [34; 35; 36; 34; 37; 38] \\ Isovaleric acid & 503-74-2 & [3] & Acidic, cheesy, herbaceous, sweaty, rancid & [34; 35; 36; 37; 39] \\ \hline
**Alcohols** & & & & \\ \hline \hline _Aliphatics_ & & & & \\ \hline
2-Methyl-1-propanol & 78-83-1 & [3] & Wine-like & [36] \\
3-Butten-1-ol & 627-27-0 & - & - & - \\
3-Methyl-3-butten-1-ol & 763-32-6 & [3] & Cooked, roasted with fruits or alcoholic undernots & [36] \\
2-Methyl-1-butanol & 137-23-6 & [40] & Green, chemical, fused oil-like sweet & [34; 35; 36] \\
1-Functional & 71-41-0 & [3] & Fresh, herbaceous-fuity-green, layered-like, & [34; 35; 36] \\
3-Methyl-2-butten-1-ol & 556-82-1 & [3] & phenolic, metallic & [34; 35; 36] \\
2-Hexanol & 626-93-7 & [3] & Fresh, lemon-like, grassy-herbaceous, & [34; 35; 36] \\
2-Heptanol & 543-49-7 & [3] & sweet-forsal undertone & [34; 36] \\
1-Octen-ol & 3391-86-4 & [3] & Mashnom, herbaceous, swory, bruchy, meaty & [37; 41; 42] \\
2-Ethly-1-hexanol & 104-76-7 & [3] & Sweet, slightly floral rose-like & [36] \\
1-Octenol & 111-87-5 & [43] & Fresh, orange-rose, sweet & [36] \\ \hline \hline _Acomatics_ & & & & \\ \hline \hline \end{tabular}
\begin{tabular}{c c c} \hline \hline
2-Phenylethanol & 60-12-8 & [3] & Rose-honey-like, floral & [34; 36; 41] \\ \hline \hline \multicolumn{3}{c}{**Aldehydes**} \\ \hline \hline Acetaldehyde & 75-07-0 & [3] & Pungent, ethereal, fruity, coffee, wine, acrid/egg & [34; 36; 41; 44; 45] \\
2-Methyl-propanol & 78-84-2 & [3] & Pungent, sour, fruity, malty, butter-yolly & [34; 35; 36] \\
2-Buttenal & 4170-30-3 & [47; 48] & & \\
3-Methylbutanal & 590-86-3 & [3] & Pungent, acrid, fruity, apple-like, almond, & [34; 36; 39; 44; 46] \\
2-Methyl-2-buttenal & 1115-13-1 & [3] & & \\
2-Perrenal & 764-39-6 & - & Pungent, green, apple, orange, tomato & [36] \\ Hexanal & 66-25-1 & [3] & Fatty, green, grassy, fruity, rancid butter-like, nutty & [34; 36; 38; 41; 46] \\
4-Methyl-2-hexneal & 5362-50-5 & - & - & - \\
2-Methyl-2-hexneal & 28467-88-1 & - & - & \\
2-Hexadienal & 80466-348-8 & [3] & Fresh, green, floral, citrus & [36] \\
4-Methylhexanal & 41065-97-8 & - & - & \\ Heptanal & 111-71-7 & [3] & Oily-fatty, rancid, pungent, fermented-fruit-like & [34; 36] \\
2-Hepprenal & 2463-63-0 & [43] & Pungent, green, fatty & [36] \\ Octanal & 124-13-0 & [3] & Fatty, citrus, orange-like, honey & [36] \\
2-4-Hepptaelal & 5910-850-4 & [49] & Fatty, green & [36] \\
2-Octenal & 2363-89-5 & [37] & Green-leafy, orange, honey-like, cognac-like & [36; 37] \\ Nonanal & 124-19-6 & [19; 43] & Fatty, orange and rose, soap-like, metallic & [36; 36] \\
2-Nonneal & 2463-53-8 & [3] & Fatty, ornis-like, wavy, dried orange peel-like, & [36; 38] \\ Decanal & 112-31-2 & [19; 49; 51] & Sweet, wavy, floral, citrus, fatty & [36] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Volatile compounds putatively identified in 8 capsule-coffee powders and espresso brews, organized by chemical family, using HS-SPME/GC \(\times\) GC-ToFMS and aroma descriptors for each compound when available in the literature.