## 3 Results and Discussion
### Odor Activity Values  
Generally, volatile compounds with OAV \(\geq 1\) are regarded as potential contributors to an aroma profile [31]. Higher OAVs correspond to a greater contribution to the aroma. Twenty-four volatile compounds had OAVs \(>1\) in all the processed XYMJ green tea samples, except for phytol acetate with OAV (0.9) in tea shoots (Table 2), and most of the key odorants had floral attributes. The top ten key odorants with the highest OAVs in the made XYMJ green tea were trans-nerolidol (10,199.4), geranylacetone (3436.5), nonanal (3190.1), (+)-\(\delta\)-cadinene (1881.0), linalool (838.0), (Z)-jasmone (465.6), cis-3-hexenyl butyrate (220.6), cis-3-hexenyl hexanoate (189.0), methyl jasmonate (125.1), and \(\beta\)-ocimene (92.4). Previous studies and the present result revealed that (E)-nerolidol was the key odorant contributing to the aroma profile of XYMJ green tea and other green teas [11; 17; 19; 32]. Multiple stresses, such as mechanical damage and low temperature, had a synergistic effect on (E)-nerolidol formation during oolong tea manufacturing [33]. (E)-Nerolidol could also be derived from the non-enzymatic degradation of phytofluene [7]. Derived from the carotenoids, the floral geranylacetone was also considered the aroma-active compound in Japanese green tea (Sen-cha) [34], summer green tea [29], and Longjing tea [35]. Based on OAV calculation, nonanal, linalool, (Z)-jasmone, and methyl jasmonate were the key odorants in premium green teas (Longjing, XYMJ, Taiping Houkui, Lu'an Guapian, etc.) [11; 36; 37; 35]. Cis-3-hexenyl hexanoate in XYMJ green tea was determined by both OAV calculation and GC-O, while (+)-\(\delta\)-cadinene was only detected by OAV calculation, which might be due to the different sample preparation techniques [11]. Therefore, a comprehensive analysis of XYMJ green tea aroma by GC-O technique is required in future studies. Figure 7: Principal coordinate analysis (**a**) and hierarchical clustering analysis (**b**) of the processed XYMJ green tea samples. The \(\beta\) diversities of volatile compounds were based on Manhattan dissimilarities. (**a**): PCoA scatter plots of the volatile compounds in the processed XYMJ green tea samples, (**b**): the dendrograms represent HCA. PERMANOVA \(R^{2}\) and \(p\) values were indicated for the two clusters of the volatile compounds, which were represented by circles of different sizes. As shown in Table 2, the key odorants in the processed XYMJ green tea samples almost belong to endogenous biosynthesis volatiles, including fatty acid-derived volatiles (FADVs), amino acid-derived volatiles (AADVs), volatile terpenes (VTs) and carotenoid-derived volatiles (CDVs) [2,41]. There are fourteen key odorants that are VTs and they present fruity and floral odors, which may contribute to the formation of the superior aroma quality of XYMJ green tea. In addition to cis-3-hexenyl hexanoate with a green odor, the FADVs, including nonanal, (Z)-jasmone, cis-3-hexenyl butyrate, methyl jasmonate, and cis-3-hexenyl valerate, could form the floral quality of XYMJ green tea. As the only AADVs with a green odor, the decrease of the methyl salicate is beneficial to the formation of the attractive aroma quality of XYMJ green tea. Derived from the carotenoids, geranylacetone and dihydroactinolide are necessary for the formation of the aroma of XYMJ green tea. To sum up, the aroma of XYMJ green tea is the comprehensive presentation of the key odorants, which are derived from multiple biosynthetic pathways. It has been reported that nine aroma-active compounds mimic the aroma quality of XYMJ green tea, including linalool, geraniol, (E)-nerolidol, nonanal, octanal, decanal, \(\beta\)-cyclocitral, \(\beta\)-ionone, and cis-3-hexenyl hexanoate [11]. Fourteen volatile compounds with high OAVs can recreate the aroma of Longjing green tea [35], and twenty-nine odorants showing OAVs \(\geq 1\) can simulate the aroma of a high-grade Chinese green tea (_Jingshan cha_) [10].