# Formation Mechanisms and Kinetic Modeling of Key Aroma Compounds During Qidan Tea Roasting
## 3 Results and Discussion
### Labeling Glucose to Infer the Source of Arona Compounds
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Compounds**} & \multirow{2}{*}{**m/z**} & \multirow{2}{*}{**Molecular Formula**} & \multirow{2}{*}{**System**} & \multicolumn{4}{c}{**Relative Distributions of Isotopologues (\%)**\({}^{\mathrm{c}}\)} \\ \cline{5-10}  & & & & **M** & **M + 1** & **M + 2** & **M + 3** & **M + 4** & **M + 5** \\ \hline \multirow{2}{*}{17} & \multirow{2}{*}{N-ethylacetamide} & \multirow{2}{*}{87} & \multirow{2}{*}{C\({}_{4}\)H\({}_{5}\)NO} & all & 100 & & & & & \\  & & & & half & 100 & & & & & \\ \multirow{2}{*}{18} & \multirow{2}{*}{Nonanoic acid} & \multirow{2}{*}{158} & \multirow{2}{*}{C\({}_{9}\)H\({}_{18}\)O\({}_{2}\)} & all & 100 & & & & & & \\  & & & & half & 100 & & & & & & \\ \hline \multirow{6}{*}{19} & \multirow{6}{*}{N-ethylacetamide} & \multirow{6}{*}{87} & \multirow{2}{*}{C\({}_{4}\)H\({}_{5}\)NO} & all & 29 & 71 & & & & & \\  & & & half & 100 & & & & & & & \\ \multirow{2}{*}{18} & \multirow{2}{*}{Nonanoic acid} & \multirow{2}{*}{158} & \multirow{2}{*}{C\({}_{9}\)H\({}_{18}\)O\({}_{2}\)} & all & 100 & & & & & & \\  & & & half & 100 & & & & & & & \\ \hline \multirow{6}{*}{18} & \multirow{6}{*}{N-ethylacetamide} & \multirow{6}{*}{158} & \multirow{6}{*}{C\({}_{9}\)H\({}_{18}\)O\({}_{2}\)} & all & 2.5:3 in the half-labeled system, which, combined with the structural features of its nitrogen-containing aromatic ring, suggests that the carbon skeleton originates exclusively from the C-2 position of glucose while the nitrogen atom is derived from the amino acid ([PERSON] et al., 2015). Notably, the pyrazine derivatives with different substituents show specific cleavage patterns: the cleavage feature at the C-2/3 position of 2-methylpyrazine,  
\end{table} 
Table 2: _Cont._ \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Compounds**} & \multirow{2}{*}{**m/z**\({}^{\mathrm{a}}\)**} & \multirow{2}{*}{**Molecular Formula**} & \multirow{2}{*}{**D\({}_{\mathrm{5}}\)-Labeled**} & \multicolumn{4}{c}{**Relative Distributions of Isotopologues (\%)**\({}^{\mathrm{b}}\)} \\ \cline{5-10}  & & & & **M** & **M + 1** & **M + 2** & **M + 3** & **M + 4** & **M + 5** \\ \hline \multirow{2}{*}{1} & \multirow{2}{*}{Furfuryl alcohol} & \multirow{2}{*}{98} & \multirow{2}{*}{C\({}_{5}\)H\({}_{6}\)O\({}_{2}\)} & all & 100 & & & & \\  & & & half & 100 & & & & & \\ \multirow{2}{*}{2} & \multirow{2}{*}{Hexanal} & \multirow{2}{*}{100} & \multirow{2}{*}{C\({}_{6}\)H\({}_{12}\)O\({}_{2}\)} & all & 100 & & & & \\  & & & half & 100 & & & & & \\ \multirow{2}{*}{3} & \multirow{2}{*}{Furfural} & \multirow{2}{*}{96} & \multirow{2}{*}{C\({}_{5}\)H\({}_{4}\)O\({}_{2}\)} & all & 100 & & & & \\  & & & half & 100 & & & & & \\ \multirow{2}{*}{4} & \multirow{2}{*}{2-Methylfuran} & \multirow{2}{*}{82} & \multirow{2}{*}{C\({}_{9}\)H\({}_{6}\)O\({}_{9}\)N} & all & 80 & & & 20 \\  & & & half & 90 & & & 10 \\ \multirow{2}{*}{5} & \multirow{2}{*}{1-Ethyl-1H-pyrrole} & \multirow{2}{*}{95} & \multirow{2}{*}{C\({}_{9}\)H\({}_{9}\)N} & all & & & & & 100 \\ \hline \hline \end{tabular}  
\({}^{\mathrm{a}}\) Molecular ion. \({}^{\mathrm{b}}\) Values were corrected by subtracting the naturally occurring percentages of \({}^{13}\)C (1.10%), \({}^{33}\)S (0.76%), and \({}^{34}\)S (4.20%) in M\({}^{\prime}\) + 1 and M\({}^{\prime}\) + 2; the loss of hydrogen observed with the molecular ion in EI-MS was also corrected in the labeled molecular ions by the ratio (M\({}^{\prime}\) – 1)/M.  
\end{table} 
Table 3: Isotopic distribution patterns of identified volatile compounds with D\({}_{5}\) labeled and half-labeled isotopic isomers detected in CAMOLA method experiments. the preferential cleavage pattern at the C-3 position of 2,5/2,3-dimethylpyrazine, and the contribution feature at the C-5/6/7 position of 2-vinylpyrazine, which together construct a precise localization profile of the glucose carbon atoms in the pyrazine ring.