## 3 Results
### Method Validation  
In order to perform the quantitation of the VFCs (2,4-heptadienal, \(\beta\)-damascenone, \(\beta\)-ionone, linalool, indole, 2-ethyl-6-methyl-pyrazine, 2-ethyl-5-methyl-pyrazine, 2-ethyl-3,6-dimethyl-pirazine, 2-ethyl-3,5-dimethyl-pyrazine and acetyl-pyrazine), for the reliable monitoring of their variations before and after roasting, the HS-SMPE-GC-MS method was validated for linearity, sensitivity, accuracy and precision in the presence of isotopically labeled IS, as described in the Materials and Methods. The linearity of the method was studied on the selected compounds by analyzing aqueous solutions at five levels of concentration within the range 0.02-2.0 \(\mathrm{\SIUnitSymbolMicro mL}\). Calibration graphs were obtained by plotting the ratio of the SIM peak areas of the analytes to IL-IS, versus the corresponding concentration (\(\mathrm{\SIUnitSymbolMicro g}\)/mL). A standard addition method was also carried out on green tea (Bancha Hojicha) infusion to simultaneously confirm the linearity and to determine the matrix effect. The resulting calibration curve equations were in the form of \(\mathrm{Y}=\mathrm{a}\) (\(\pm\mathrm{s}\mathrm{d}\))\(\mathrm{X}+\mathrm{b}\)(\(\pm\mathrm{s}\mathrm{d}\)), the obtained results are shown in Table 3.  
The correlation coefficient found (\(\mathrm{r}^{2}\) range from 0.981 to 0.999) confirmed the linearity of the response over three orders of concentration of the analytes, as well as in the presence of the complex matrix. The matrix effect percentage (ME%) was evaluated by comparing the calibration curve slopes obtained from standard solutions and samples spiked with standards; values greater and lower than 0% indicated a positive matrix effect (ionic increase) and negative matrix effect (ionic suppression), respectively. Matrix effect values were considered negligible, al \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**RI 1a**} & \multirow{2}{*}{**Name**} & \multirow{2}{*}{**Odor Quality**} & \multicolumn{3}{c}{**Relative Percentage Content (\%) 1c**} \\ \cline{5-6}  & & & & **Bancha** & **Bancha Hojicha** & **Bancha 180 \({}^{\circ}\)C** \\ \hline
11 & 1097 & \({}^{\mathrm{b}}\) & Linalool & Floral sweet & 3.55 & 4.39 & 3.56 \\  & 1097 & Linalool-d5 (IL-IS) & & & & \\  & 1099 & Nonanal & Grassy & 2.31 & 1.25 & 1.03 \\ \hline
12 & 1101 & \({}^{\mathrm{b}}\) & Acetylpyrazine & Nutty & 0.85 & 3.52 & 4.03 \\ \hline
13 & 1125 & 2,6-nondienal & Fatty, cucumber-like & 0.42 & 0.67 & 4.87 \\  & 1256 & \({}^{\mathrm{b}}\) & Geraniol & Floral, sweet & 4.70 & 10.03 & 14.65 \\ \hline
15 & 1355 & \({}^{\mathrm{b}}\) & \(\beta\)-damascenone & Floral, honey-like & 1.98 & 1.77 & 0.32 \\ \hline
16 & 1362 & \({}^{\mathrm{b}}\) & \(\beta\)-damascone & Sweet, honey-like & 0.45 & 0.22 & 0.20 \\  & 1371 & Benzyl alcohol & Sweet & 0.49 & 0.23 & 0.54 \\  & 1397 & _cis_-jasmone & Floral & 1.70 & 1.23 & 1.02 \\ \hline
17 & 1431 & \({}^{\mathrm{b}}\) & \(\beta\)-ionone & Woody, floral, & 5.07 & 2.73 & 2.12 \\  & 1443 & Dodecanal & Citrus & 1.50 & 3.15 & 3.43 \\ \hline
18 & 1465 & \({}^{\mathrm{b}}\) & Eugenol & Spicy & 0.40 & 0.53 & 0.99 \\ \hline
19 & 1493 & \({}^{\mathrm{b}}\) & Indole & Animal-like & 3.85 & 3.56 & 4.87 \\  & 1519 & \(\delta\)-cadinene & Spicy, woody & 0.65 & 1.06 & 0.88 \\  & 1556 & Nerolidol & Floral, fruity & 3.02 & 2.55 & 3.98 \\  & 2063 & Phytol & Floral & 5.99 & 6.78 & 6.03 \\ \hline \hline \end{tabular}  
* RI, retention index as determined on HP-5 MS column using a homologous series of n-alkanes (C8–C40). \({}^{\mathrm{b}}\) Determined by injecting reference standard. \({}^{\mathrm{c}}\) The relative percentages represent the average of 3 samples of each type of tea, with an RSD% between 10 and 35.  
\end{table} 
Table 2: _Cont._ways in a range of \(-\)9.5 to +4.5% for all studied analytes. Indeed, the curve slopes obtained with standard additions did not differ significantly from those in neat solution (p n.s.).