# Volatile Profile of Nuts, Key Odorants and Analytical Methods for Quantification
## 5 Volatile Profile of Nuts after Thermal Treatments
### Roasting Thermal Processing
compounds related to this reaction in nuts are benzyl alcohol, 2,3-pentanedione, furfural, phenylacetaldehyde, toluene, 2,5-dimethyl-4-hydroxy-3(2H)-furanone, 2-furfurylthiol and some nitrogen-containing compounds including pyrazines such as 2,5-methylpyrazine, 2-methylpyrazine, dimethylpyrazine and trimethylpyrazine [36; 59; 61]. Some reported compounds are formed by the Strecker degradation reaction of amino acids in the Maillard reaction such as 2-methylbutanal, 3-methylbutanal and 2-acetyl-1-pyrroline [42]. Benzaldehyde is produced from phenylalanine under heat [61]. Benzeneacetaldehyde is a compound formed from phenylalanine by the action of polyphenol oxidase, and has been found in freshly roasted almonds, with honey-like scent, harsh, and hawthorn odor descriptors [22]. One important reaction is the degradation of sugars in the caramelization process [42]. In this process, heterocyclic oxygen furans are formed such as furfural. Another important reaction is fatty acid autoxidation. Hexanal and 2-nonenal, among others, are products of the degradation of linoleic acid; meanwhile, for example, nonanal and 2-decneal come from oleic acid [61]. Moreover, lipid degradation is a very important process for the volatile profiles of nuts, in which some aldehydes, alcohols and ketones are formed, being responsible for the desire toasted flavor [42]. Alcohols were also generated through lipid degradation such as 1-octen-3-ol, which comes from the thermal decomposition of methyl linoleate hydroperoxide, and contributes to a herbaceous aroma, whereas 1-butanol is formed from the decomposition of linolenic acid and is responsible for an unripe apple aroma [61]. Regarding ethanol, it was at high concentration among the volatile compounds in roasted cashew nut, which contributes to the formation of esters that usually have fruity odors [65]. Acetone found in roasted cashew is a result of the reaction of D-xylose with valine, while heptane does not contribute to aroma [65]. Sulfur-containing compounds also increase during the roasting process because of the degradation of sulfur-containing amino acids, such as cysteine and methionine. Sulfur compounds such as dimethyl sulfide give a taste of fresh onions to the oils. In relation with terpene compounds, in a study with pistachios, it was found that VOCs analysis shows that Argentinean pistachio nuts are rich in monoterpenes, mainly limonene (citrus, mint), \(\alpha\)-pinene (pine, turpine), and 3-carene (lemon, resin) [64]. According to the mentioned work, it is possible to define the limonene as a marker for unroasted pistachio, while \(\alpha\)-pinene and 3-carene seem to be associated with roasted pistachio with and without salt. In this sense, the perception of roasting is associated with increased amounts of \(\alpha\)-pinene and 3-carene in roasted pistachio, while the raw sample is associated with higher amounts of limonene. Finally, it seems that any difference was reported due to the addition of salt. To sum up, changes in the volatile profile due to the roasting treatment significantly affect the quality attributes of nuts, obtaining appreciable and desired changes in flavor. For example, the presence of 4-hydroxy-2,5-dimethyl-3(2H)-furanone in roasted hazelnuts was detected at high concentrations. This compound is formed after the dehydration of reducing monosaccharides. The changes in concentration of this volatile compound explain the differences in sensorial perception (popcorn-like, coffee-like and caramel) after eating roasted hazelnuts; meanwhile, in raw hazelnuts, the perception is associated with a fruity and nutty aroma [59].