## 5 Aroma Profile of Nut Products After and Before Roasting Conditions
### Hazelnuts  
A total of 39 compounds contributing to the characteristic aroma of raw Turkish hazelnuts were identified. These compounds were categorized as ketones, aldehydes, alcohols, aromatic hydrocarbons, and furans. The most abundant compounds were hexanal (2780 ug/kg), 2-pentanone (1603 ug/kg), 2-pentanon (1509 ug/kg), (E)-3-penten-one (832 ug/kg), 3-methyl-1-butanol (482 ug/kg), 1-pentanol (344 ug/kg), and 2,3,5-trimethylfuran (259 ug/kg) [61]. Furthermore, [PERSON] et al. (2022) reported associations between specific molecules and aroma qualities in various hazelnut varieties. For instance, hexanal was linked to green aromas, while 3-methylbutanal and 2-methylbutanal were associated with malty notes. Caramel aromas were connected to 2-acetyl-1,4,5,6-tetrahydropyridine and 2-acetyl-3,4,5,6-tetrahydropyridine, and 3-methyl-4-heptanone was linked to fruity notes [15]. [PERSON] et al. (2012) identified several odor-active compounds in raw Italian hazelnuts, including hexanal (1790 ug/kg), acetic acid (310 ug/kg), linalool (280 ug/kg), octanal (163 ug/kg), 5-methyl-4-heptanone (59 ug/kg), and 3-methylbutanal (34 ug/kg), along with other traces of VOCs [62]. After the roasting process, the hazelnut volatile profile undergoes significant changes. Some existing molecules are enhanced through various reactions. Additionally, non-enzymatic reactions can lead to the formation of new molecules, contributing to the characteristic aroma of roasted products, often described as coffee-like or popcorn-like. [15]. [PERSON] et al. (2023) reported the presence of or increases in several volatile compounds in roasted hazelnuts that were not detected in raw samples. These compounds included 2-methylpropanal (4875 ug/kg), 3-methylbutanal (27,445 ug/kg), 2-pentanone (2772 ug/kg), \(\alpha\)-pinene (598 ug/kg), and 1-cyclopentyl ethenone (1562 ug/kg), as well as numerous other minor compounds, while other compounds were found in minor quantities, such as hexanal (2517 ug/kg), 2-methylbutanal, 2-ethyl-5-methylfuran, and xylene [61]. Moreover, 5-methyl-2-hepten-4-one was identified as a major ketone that contributes to the typical roasty aroma of hazelnuts [63]. [PERSON] et al. (2012) conducted a comprehensive analysis of the volatile organic compound (VOC) profile of roasted hazelnut paste. The study identified several key VOCs, including 3-methylbutanal, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, (E,E)-2,4-decadienal, hexanal, octanal, (Z)-2-nonenal, and acetic acid. Furthermore, the authors proposed that the initial amino acid composition of raw nuts can significantly impact the formation of aroma compounds during the roasting process [62]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**NUTS** & & **Main VOCs** & **References** \\ \hline \multirow{8}{*}{Raw pistachios} & \(\bullet\) & \(\alpha\)-Pinene (1.68 to 333 ug/g) & \\  & \(\bullet\) & Nonanal (0.63 ug/g) & \\  & \(\bullet\) & 1-Methylpyrrole (48 ug/g) & \\  & \(\bullet\) & Acetic acid (3.3 ug/g) & \\  & \(\bullet\) & Hexanal (9.1 ug/g) & [67; 68; 69] \\  & \(\bullet\) & Hexanol (1 ug/g) & \\  & \(\bullet\) & \(\beta\)-Pinene (6.5 ug/g) & \\  & \(\bullet\) & Limonene (1 ug/g) & \\  & \(\bullet\) & Benzyl acetate (1.8 ug/g) & \\ \hline \multirow{2}{*}{Roasted pistachios} & \(\bullet\) & \(\alpha\)-Pinene (2.4 to 3 ug/g) & \\  & \(\bullet\) & Limonene (3.5 to 4.96 ug/g) & [70; 71; 72] \\ \cline{1-1}  & \(\bullet\) & Nonanal (0.86 ug/g) & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: _Cont._One of the most important classes of compounds released during the roasting process is pyrazines. Exclusively detected in roasted hazelnuts, pyrazines can reach concentrations of 4608 ug/kg. The most abundant pyrazines include 2,5-dimethylpyrazine, methylpyrazine, and 2-ethyl-5-methylpyrazine. As previously reported, pyrazines contribute to hazelnuts' roasty and sweet flavor profile. Similarly to pyrazines, furans are also exclusively detected at high levels in roasted hazelnuts. The most common furans include 2-ethyl-5-methylfuran and 2,3,5-trimethylfuran.