## 3 Results and Discussion
### Variation of Volatile Compounds in XYMJ Green Teas  
The volatile compounds in XYMJ green teas were successfully determined by the HS-SPME and GC-MS. A total of 39 volatile compounds were tentatively identified, mainly including alcohols, aldehydes, esters, ketones, hydrocarbons and other compounds. Various change trends of the volatile compounds in XYMJ green teas were shown in the heat map (Figure S1), and the contents of identified volatile compounds in XYMJ green teas are listed in Table 2.  
The dominant identified alcohol compounds in XYMJ green teas were geraniol, linalool, cis-nenerolidol, \(\delta\)-cadinol, 1-octen-3-ol and 3-decyn-2-ol. The total content of alcohol compounds decreased gradually in the spring season, while increased in the later autumn season. As shown in Figure 2, the contents of 1-octen-3-ol, 3-decyn-2-ol and linalool varied similarly in the spring season, and 1-octen-3-ol, 3-decyn-2-ol and \(\delta\)-cadinol varied similarly in the autumn season. Among the identified alcohol compounds, terpenic alcohols, such as linalool, geraniol, cis-nerolidol and \(\delta\)-cadinol, are the key aroma compounds for XYMJ green teas. The variation of geraniol displayed the same tendency with the total terpenic alcohols. The variation of linalool, geraniol and \(\delta\)-cadinol presented increased tendency in the later autumn season, while cis-nerolidol decreased in the autumn season. The total content of terpenic alcohols decreased gradually in the spring season, while it increased in the later autumn season. Released from their corresponding glycoside precursors, the floral-fruity terpenic alcohols contribute significantly to the tea aroma due to their high contents and low thresholds [23]. Figure 1: Principal coordinate analysis (**A**,**B**) and hierarchical clustering analysis (**C**,**D**) of XYMJ green teas. The \(\beta\) diversities of non-volatile compounds and volatile compounds were based on Manhattan dissimilarities. (**A**,**B**): PCoA scatter plots of the non-volatile compounds and volatile compounds in XYMJ green teas, (**C**) (non-volatile compounds) and (**D**) (volatile compounds): the dendrograms represent HCA. PERMANOVA \(R^{2}\) and \(p\) values are indicated for the 3 clusters of the metabolic profile, which were represented by the circles of different sizes. Due to their relatively low odor threshold values, the aldehydes have been speculated to play important roles on the formation of clean aroma [24]. As shown in Figure 3, the content of aliphatic aldehydes, including hexanal, heptanal, nonanal and decanal, were much higher than the other aldehydes. During the spring season, the hexanal decreased from 15.04 ug/L to 5.41 ug/L, while the \(\beta\)-cyclodextrin increased from 2.31 ug/L to 3.39 ug/L. The aliphatic aldehydes and benzaldehyde presented a similar tendency in the autumn season. Hexanal usually represented green and grassy notes, \(\beta\)-cyclodextrin represented fruity aroma notes [25], the decrease of hexanal and the increase of \(\beta\)-cyclodextrin would contribute to the good XYMJ green tea aroma formation. The contents of hexanal and heptanal in XYMJ spring teas were higher (\(p<0.05\)) than that in XYMJ autumn teas, while the contents of nonanal and decanal had no significant differences between the XYMJ spring and autumn teas. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & \multirow{2}{*}{**Retention Time (min)**} & \multirow{2}{*}{**CAS No.