## 3 Results and Discussion
### Key Volatile Compounds Identified in OOT and TOT  
The key volatile compounds of OOT and TOT are summarized in Table 2, and their relative contents are illustrated in a heatmap (Figure 3A). Among the 40 volatile compounds commonly shared by TOT and OOT, the main aroma components were linalool, hotrienol, linalool oxide III, indole, \(\beta\)-myrrene and \(\beta\)-ocimene. Indole, linalool, and their oxides were the dominant aroma components of oolong tea, consistent with previous research [24; 25]. Isoeugenol was only detected in OOT, while \(\alpha\)-cedrene, \(\alpha\)-curcumene and \(\alpha\)-cymene were detected exclusively in TOT at trace levels. Twenty volatiles were significantly different between TOT and OOT, including three alcohols (benzyl alcohol, linalool and nerolidol), nine alkenes (1,3,5,7-cyclooctatetraene, \(\alpha\)-farnesene, \(\alpha\)-copaene, styrene, \(\beta\)-caryophyllene, \(\beta\)-myrceene, (E)-\(\beta\)-farnesene, limonene and \(\beta\)-ocimene), one aldehyde (benzene acetaldehyde), three ketones (_trans_-\(\beta\)-ionone, (_Z_)-jasmone and \(\alpha\)-ionone), one ester (hexanoic acid hexyl ester) and three other types of substances (indole, p-xylene and1-(1H-pyrrol-2-yl)-ethanone). The differences between samples mainly occurred with alkenes. Figure 2: Characteristics of the volatile components of TOT and OOT. (**A**) The differences in six volatile categories between TOT and OOT. (**B**) The Wickremasinghe-Yamanishi ratio of TOT and OOT. \(t\)-test was used to identify significant differences (ns = not significant; * \(p\) < 0.05). (**C**) The Owuor’s flavor index of TOT and OOT. TOT: Tibet oolong tea; OOT: Origin oolong tea. Due to the large number of volatiles, we focused on 16 major volatiles that play key roles in tea fragrance [15; 26; 27]. The contents of benzene acetaldehyde (floral, rose, cherry-like aroma), (Z)-jasmone (sweet, flower, violet-like aroma), copaene (wood aroma), \(\beta\)-caryophyllene (wood aroma) and benzyl alcohol (sweet, floral, rose-like, caramel-like aroma) were significantly higher in TOT than in OOT (Figure 3B). Benzyl alcohol is hydrolyzed from glycosidic precursors in tea leaves under acidic or enzymatic actions to produce aroma compounds [28]. The environmental conditions at high altitudes were  
Figure 3: Analysis of key volatile compounds in OOT and TOT. (**A**) Heatmap showing differences in 45 key volatile compounds. Red and green represent positive and negative fold changes. (**B**) Differences in 16 key aroma compounds in TOT and OOT. Relative content in the vertical scale is shown by means \(\pm\) SD (n = 3). \(t\)-test was used to identify significant differences (\({}^{*}p<0.05;\)\({}^{**}p<0.01\)). extremely favorable for the accumulation of benzyl alcohol glycosides in tea leaves. However, the contents of indole ( floral, animal-like aroma), \(\beta\)-myrcene (wood, resinous, musty aroma), linalool ( floral, sweet, grape-like, woody aroma), nerolidol ( floral, apple, green aroma), \(\alpha\)-farmesene (wood, green, floral, herbal aroma), \(\beta\)-ocimene (warm, floral, herbal, sweet aroma) and 1,3,5,7-cyclooctatetraene (solvent-like aroma) in TOT were significantly lower than those in OOT (Figure 3B). Indole has a low aroma threshold and high odor activity value that greatly contributes to the floral aromas of oolog tea [25]. Linalool and its oxides are the main aroma contributors among green, black and oologous teas [29; 30; 31; 32]. The content of \(\alpha\)-farmesene, nerolidol, indole and benzyl alcohol increase significantly during the rolling step of oolong tea processing [33]. In this study, \(\alpha\)-farmesene, nerolidol and indole showed the same trend in the two samples, indicating that their content may be simultaneously induced by stress. Interestingly, some volatile compounds, such as \(\alpha\)-cedrene (wood and spice aroma), \(\alpha\)-curcumene (herbal aroma) and O-cymene (aromatic aroma), that had never been detected in 'Wuyedancong' tea before were found in TOT.