## 3 Results and Discussion
### PTR-ToF-MS: Determination of Volatile Compounds from Spirulina  
By the PTR analysis applied on the headspace of spirulina powders, a total of 41 tentatively identified compounds in the range of measured masses (27.022 \(m/z\) 157.129), were registered with average values above 1 ppbv. All the aroma compounds detected with their amounts (average of three replicates \(\pm\) standard deviation) were reported in Table 2. Among these we found many typical class aroma compounds of microalgae such as furans, sulfides, alkanes, aldehydes, alcohols, ketones, esters and pyrazine, in agreement with many authors [29; 30; 31]. Overall, the signal detected at \(m/z\) 61.028 and identified as acetic acid which is a typical sour and pungent odor with low thresholds and high concentrations in many microalgae species was the most emitted compound [32]. The other higher emitted compounds were represented by methanol (\(m/z\) 33.033) which is characterized by a distinctive alcoholic odor similar to that of ethanol, acetaldehyde (\(m/z\) 45.033) which has \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{N}^{\circ}\) & **COMPONENT 1** & **LR1 2** & **LR1 3** & **Spirulina (\%)** \\ \hline
1 & _trans_-disopropylethylene & 709 & 713 & tr \\
2 & 2-propylfuran & 785 & 793 & tr \\
3 & 5-heptanal, 2,6-dimethyl- & 1038 & 1044 & tr \\
4 & 2,5-dimethylcyclohexanol & 1086 & 1090 & 0.1 \(\pm\) 0.02 \\
5 & \(\beta\)-cyclocitral & 1190 & 1197 & tr \\
6 & _cis_-geranylacetone & 1431 & 1427 & tr \\
7 & _trans_-\(\beta\)-ionone & 1465 & 1460 & 1.9 \(\pm\) 0.03 \\
8 & pentadecane & 1509 & 1512 & 6.2 \(\pm\) 0.06 \\
9 & 2(4H)-benzofurano, 5,6,7,7a- & 1520 & 1525 & 0.3 \(\pm\) 0.02 \\  & tetrahydro-4,4,7a-trimethyl- & 10 & 1612 & 5.0 \(\pm\) 0.04 \\
10 & hexadecane & 1609 & 1612 & 1.4 \(\pm\) 0.05 \\
11 & 8-heptadecene & 1675 & 1680 & 1.4 \(\pm\) 0.05 \\
12 & heptadecane & 1709 & 1711 & 85.0 \(\pm\) 2.15 \\ \hline \hline \end{tabular} 1
[FOOTNOTE:1]Footnote 1: The components are reported according to their elution order on apolar column; 2
[FOOTNOTE:2]Footnote 2: Linear Retention Indices measured on apolar column; 3  
\end{table} 
Table 1: Chemical composition (percentage mean values \(\pm\) standard deviation) of vapor phase of spirulina. green-like and hay-like odor notes, and propanal (\(m/z\) 59.049) with a pungent odor. All these mentioned compounds represent over 65% of the total emission (Table 2). On the contrary, all the other detected compounds show a significantly reduced emission level and often less than 1% of the total. Among these we found signals linked to nitrogen compounds (\(m/z\) 80.050, 87.091, 95.061 and 109.076) and sulfur-containing compounds (\(m/z\) 49.011 and 91.057) that are abundant in dried seaweeds and are both related to fish odors [29; 33]. In particular, sulfur compounds are associated with the aroma of marine crustaceans such as cooked shrimp/cooked seafood, marine and fishy odors, while the pyrazines tend to deliver nutty notes [34]. Among the chemical compounds with low emission rates are those linked to nitrogenous (\(m/z\) 80.050, 87.091, 95.061 and 109.076) and sulfurous ones (\(m/z\) 49.011 and 91.057) that are detected in dried seaweeds and are related to fish odors [34]. In particular, sulfur compounds have been associated with the aroma of marine crustaceans such as shrimp and cooked seafood, while pyrazines tend to provide nutty notes [34]. Also, the furans (\(m/z\) 83.083 and 97.085) which were detected in low amounts have been previously reported as characteristic aromas of microalgae [35]. PTR analysis has already been used in our previous work in order to detect the VOCs present, even in traces, in dried hop leaves [28].