## 2 Results and Discussion
### Tea infusion Volatile Profiling by IS-SPME-GC-MS  
As a first step, GC-MS analyses acquired in full-scan mode enabled a comprehensive mapping of the volatile fraction of tea infusions. Volatiles were reliably identified by their EI-MS fragmentation patterns, compared to those present in commercial libraries ([PERSON] [39] and NIST 2014 [40]). The acceptability criteria for putative identification were direct match factor (DMF) > 900 and linear \(I^{T}{}_{s}\) tolerance \(\pm\) 5 units. When available, pure reference compound confirmation was performed. Table 1 reports a list of 44 volatile marker compounds together with their retention times, experimental \(I^{T}{}_{S}\), odor descriptors, and presence in analyzed samples. Although the number of detected and reliably identified volatiles was lower compared to the GC\(\times\)GC methodology [2; 3] adopted in previous investigations, the proposed strategy with IS-SPME-GC-MS allowed for efficient mapping of the most relevant markers carrying information about tea aroma profile, plant origin, and manufacturing practices. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & **Compound Name** & \begin{tabular}{c} \(t_{R}\) \\ **min** \\ \end{tabular} & \(I^{T}{}_{S}\) & **Odor** & **Ceylon** & **Assam** & **Azores** & \
\begin{tabular}{c} **Darjeeling** \\ **Castleton** \\ \end{tabular} &
\begin{tabular}{c} **Darjeeling** \\ **Testa** \\ **Valley** \\ \end{tabular} & **Kenya** & **Yunnan** \\ \hline
1 & 3-Methyl butanal * & 2.61 & 541 & Malty & d & d & d & d & d & d \\
2 & 2-Methyl butanal * & 2.70 & 566 & Malty & d & d & d & d & d \\
3 & (_E_)-2-Pentenal & 4.10 & 725 & Green, apple & d & d & nd & d & d & nd \\
4 & (_Z_)-2-Penten-1-ol & 4.85 & 788 & - & d & d & nd & nd & d & nd \\
5 & Hexanal * & 5.19 & 816 & Grassy-green & d & d & d & d & d & d \\
6 & (_E_)-2-Hexanal & 6.82 & 856 & Bitter, almond & d & d & d & d & d & d \\
7 & 1-Hexanol & 7.65 & 873 & Fruity & nd & nd & nd & d & d & d \\
8 & 2-Hepbutane & 8.40 & 890 & Sweet, fruity & d & d & nd & d & nd & nd \\
9 & (_Z_)-4-Hepmetal * & 8.48 & 896 & Fishy & d & d & nd & d & d & d \\
10 & Heptanal & 8.79 & 899 & Oil, fatty & d & d & d & d & d & d \\
11 & (_E_)-2-Heptrenal & 11.10 & 953 & Fatty, & d & d & nd & nd & d & nd \\  & & & & almond-like & & & & & & & \\
12 & Benzaldehyde & 11.10 & 954 & & & & & & & & \\  & & & & & & & & & & & \\
13 & 6-MethylS-hepten-2- & & 12.42 & 984 & Pungent, green & d & d & nd & d & d & nd \\
14 & (_E_,_)-2-4-Heptdiagneal & 12.79 & 993 & Fatty, rancid & d & d & nd & d & d & nd \\
15 & (_E_,_)-2-4-Heptdiagneal & 13.43 & 1008 & Fatty, rancid & d & d & nd & d & d & d \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of the targeted volatiles detected in selected tea infusions by IS-SPME-GC-MS together with retention times (\(t_{R}\) min), experimental \(I^{T}\), and odor descriptors as reported in reference literature [12; 26; 27; 41; 42]. Detected (d) and non-detected (nd) analytes are also reported for each tea sample; moreover, Ceylon tea is rendered as an average profile obtained from different quality grades. Analytes with an asterisk (*) are the key odorants confirmed by sensorics and subjected to accurate quantification in this study. Results on the volatile profiling showed a different distribution of analytes within the selected samples; Ceylon and Darjeeling Testa Valley (India) were characterized by a more complex volatile fraction, showing a matching of 42 detected analytes over 44 targets. The same outcome could not be observed with the other teas from Darjeeling (Castleton), where only 26 volatiles were detected, demonstrating how different tea gardens located in the same country lead to distinctive products. On the other hand, tea samples from Azores (Portugal) and Yunnan (China) showed a less complex fraction of volatiles, also in terms of key aroma compound distribution; indeed, within all identified analytes, only 15 compounds were mapped in Azores tea and 23 in Yunnan tea.