## 2 Results and Discussion
### PTR-ToF-MS Results and Comparison with HS-SPME GC-MS Findings
Statistical tests were performed on the new matrix in an attempt at understanding the impact of these VOCs on the characterization of the different mascarpone cheese samples. The results obtained for the twelve experimental modes were visualized by means of principal component analysis (PCA), with each point representing a distinct sample (Figure 3), maximizing explained variability in two dimensions. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**Chemical Class**} & \multicolumn{2}{c}{**Protonated Ion**} \\ \cline{3-4}  & & _m/z_ & **Sum Formula** \\ \hline Ethanol & Alcohols & 47.049 & C\({}_{2}\)H\({}_{7}\)O\({}^{+}\) \\
2-Propanone & Ketones & 59.049 & C\({}_{3}\)H\({}_{7}\)O\({}^{+}\) \\ Acetic acid & Organic acids & 61.028 & C\({}_{2}\)H\({}_{5}\)O\({}_{2}\)\({}^{+}\) \\
2-Butanone & Ketones & 73.065 & C\({}_{4}\)H\({}_{9}\)O\({}^{+}\) \\
1,2-Propanediol = Propylene glycol & Alcohols & 77.060 & C\({}_{3}\)H\({}_{9}\)O\({}_{2}\)\({}^{+}\) \\
2-Pentanone/3-Buten-1-ol, 3-methyl- & Ketones/Alcohols & 87.080 & C\({}_{5}\)H\({}_{11}\)O\({}^{+}\) \\
2-Butanone, 3-hydroxy- (B) / Butanoic acid/Acetic acid ethyl ester & Ketones/Organic acids/Esters & 89.060 & C\({}_{4}\)H\({}_{9}\)O\({}_{2}\)\({}^{+}\) \\ Toluene & Hydrocarbons & 93.070 & C\({}_{7}\)H\({}_{9}\)\({}^{+}\) \\ Furfural & Furans & 97.028 & C\({}_{5}\)H\({}_{5}\)O\({}_{2}\)\({}^{+}\) \\
2-Hexanone & Ketones & 101.096 & C\({}_{6}\)H\({}_{13}\)O\({}^{+}\) \\ Benzaldehyde & Aldehyde & 107.049 & C\({}_{7}\)H\({}_{7}\)O\({}^{+}\) \\
5-Methyl-delta-valerolactone & Lactones & 115.075 & C\({}_{6}\)H\({}_{11}\)O\({}_{2}\)\({}^{+}\) \\
2-Heptanone & Ketones & 115.112 & C\({}_{7}\)H\({}_{15}\)O\({}^{+}\) \\ Hexanoic acid & Organic acids & 117.091 & C\({}_{6}\)H\({}_{13}\)O\({}_{2}\)\({}^{+}\) \\
2,4-Dimethyl-1-heptrene & Hydrocarbons & 127.148 & C\({}_{9}\)H\({}_{19}\)\({}^{+}\) \\
2-Octanone & Ketones & 129.127 & C\({}_{8}\)H\({}_{17}\)O\({}^{+}\) \\
1-Hexanol, 2-ethyl- & Alcohols & 131.143 & C\({}_{8}\)H\({}_{19}\)O\({}^{+}\) \\
2-Nonanone & Ketones & 143.143 & C\({}_{9}\)H\({}_{19}\)O\({}^{+}\) \\ Octanoic acid & Organic acids & 145.122 & C\({}_{8}\)H\({}_{17}\)O\({}_{2}\)\({}^{+}\) \\ Oxime-, methoxy-phenyl- & Oxime & 152.071 & C\({}_{8}\)H\({}_{10}\)NO\({}_{2}\)\({}^{+}\) \\
2-Undecanone & Ketones & 171.174 & C\({}_{11}\)H\({}_{23}\)O\({}^{+}\) \\ Heptane, 2,2,4,6,6-pentamethyl & Hydrocarbons & 171.211 & C\({}_{12}\)H\({}_{27}\)\({}^{+}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Volatile compounds detected by both Proton Transfer Reaction-Mass Spectrometry coupled to a Time of Flight mass analyzer (PTR-ToF-MS) and SPME/GC-MS in association with mascarpone samples. Separation among Mascarpone samples according to the first two components accounted for about 62% of the total variance. It is possible to highlight how the replicates belonging to the same sample generally clustered together. In addition, a good separation among the different samples is also depicted. Considering all variables connoting the panel of different mascarpone cheese analyzed, it is mandatory to underline that the studied diversity in terms of different producers and classic versus delatcosed was not selected in order to delve into the effect of these parameters. In fact, it was just a heterogeneous panel selected in order to provide a broad description of the overall VOCs associated with this traditional dairy production. However, it is possible to foresee some preliminary differences, such as clear groups among mascarpone cheese samples belonging to the same manufacturer and a general (more or less pronounced) separation between classic and delatcosed samples within the same producer (Figure 3). These pieces of evidence suggest the need for further studies with tailored sampling in order to test the potential of a PTR-based approach as a discriminatory tool to monitor these variables.