## 3 Results and Discussion
### Key Odor Contributors to Shaken Black Tea Infusion
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c} \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Compounds**} & \multicolumn{3}{c}{**FL vs. S1**} & \multicolumn{3}{c}{**S1 vs. S2**} & \multicolumn{3}{c}{**S2 vs. S3**} & \multicolumn{3}{c}{**S3 vs. F**} & \multicolumn{3}{c}{**F vs. D**} \\ \cline{3-14}  & & **Log.FC** & **VIP** & **Type** & **Log.FC** & **VIP** & **Type** & **Log.FC** & **VIP** & **Type** & **Log.FC** & **VIP** & **Type** & **Log.FC** & **VIP** & **Type** \\ \hline
234 & (E)-Germanyylactone & & & & & & & & & & & 1.42 & 1.58 & Up \\
235 & (F)-p-\(\beta\)-lonome & & & & & & & & 1.83 & 1.79 & Up \\
**Other (2)** & & & & & & & & & & & & 1.04 & 3.50 & Up & 1.81 & 3.78 & Up \\
237 & Dimethyl sulfide & 1.54 & 2.68 & Up & & & & & & & & & & \\
241 & Indide & & & & & & & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._The analysis of the upset plot (Figure 2C) showed that there were numerical overlaps and differences in the differential volatile compounds, indicating that there were common and unique volatile compounds presented between different comparison groups. Several specific compounds can be detected in each comparison group, indicating that these different volatile components were significantly affected by the processing. There were 18, 11, 5, 3, and 1 unique differential metabolites in F vs. D, S3 vs. F, FL vs. S1, S2 vs. S3, and S1 vs. S2, respectively. For example, dimethyl sulfide is an upregulated differential compound in four groups (FL vs. S1, S2 vs. S3, S3 vs. F, F vs. D), indicating that its content was affected by most of the processes during the whole process of SBT processing. Furthermore, the HCA analysis of the differential metabolites was conducted (Figure 3), in which the color of intensity normalized scale from red to blue indicated the content of compounds from high to low. These differential volatile compounds were assigned to three classes based on the dendrogram: 13 compounds in Class I, 9 compounds in Class II, and 39 compounds in Class III. Figure 3: A total of 61 volatile compounds were shown on the heat map, selected by VIP \(>\) 1, \(p\)\(<\) 0.05, and 1 log\({}_{2}\)FC \(>\) 1. The compounds in Class I mainly have high content in the shaking stage, including 1-octen-3-ol, indole, etc. 1-Octen-3-ol is an oxidation degradation product of linoleic acid with cucumber and mushroom aroma [33] and is one of the characteristic aroma components of black tea [34]. Studies have shown that wounding stress during the shaking process activates CsTSB2 and induces the accumulation of indole [12]. Indole is the main aroma component of Oriental Beauty tea and plays a positive role in forming its unique aroma quality [12]. The compounds in Class II showed the highest content in the fermentation process, such as (E,Z)-3,6-nonadien-1-ol, (E,Z)-2,6-nonadien, 2-methylpropanal, (E,E)-2,4-hexadien, etc. (E,Z)-3,6-nonadien-1-ol exhibited sweet, green, fruity odor [35]; (E,Z)-2,6-nonadien showed cucumber odor [27]; 2-methylpropanal had a kind of malty odor [30]; (E,E)-2,4-hexadien had a sweet, green aroma [35]. The compounds in Class III exhibited the highest content in the drying process, including (E)-\(\beta\)-ionone, decanal, dimethyl sulfide, 2-pentylfuran, 2-ethylfuran, (E,E)-2,4-heptadien, etc. (E)-\(\beta\)-Ionone had floral odor [31]; decanal and 2-pentylfuran showed fruity odor [4; 36]; dimethyl sulfide exhibited cabbage odor [37]; 2-ethylfuran had a kind of caramel-like aroma [38]; (E,E)-2,4-heptadien had fatty, green odor [35]. These components play a positive role in the formation of aroma quality of SBT.