## 3 Results and Discussion
### Determination of Characteristic Volatiles in WRTs with Different Cultivars  
A total of 18 key differential VFCs were recognized as the aroma-active compounds in WRTs, most of which belonged to class A and class C with the \"floral & fruity\" and \"roasted & caramel\" scents in Table 1, and they were defined as the potential characteristic key odorants in the WRTs with different cultivars. In theory, the concentration distribution trends of the potential key odorants were supposed to be proportional to the order of their AI values among different WRTs. However, some inconsistent appearances between the stoichiometry and sensory results were also observed, probably due to instrumental and sensory errors, as well as high odor thresholds but not sufficiently large concentration differences among different WRTs presented by some odorants. To ensure the accuracy of the characteristic key odorants in WRTs with different cultivars, the potential odorants with inconsistent distribution trends between the average peak areas and AI values were removed. Sixteen odorants were maintained, with various distribution trends among the four types of WRTs (Figure 5). Methyl salicate, \(p\)-cymene, 2,5-dimethylpyrazine, and 1-furfurylpyrole presented the highest concentration levels (\(p<0.05\)) and AIs (2.8-3.3) in the DHP samples; thus, they were identified as the characteristic key odorants of DHP. Figure 4: Radar graph based on the total aroma intensity (AI) values of the six odor classes for the four types of Wuyi rock teas (WRTs). The pyrrole and pyrazine derivatives were believed to be newly formed through Maillard reactions during WRT processing, especially after the final full firing step [3; 12], which were generated from Strecker degradations between theanine and \(D\)-glucose under high temperatures [4; 9]. Although 2,5-dimethylpyrazine and 1-furfurylpyrrole have been reported as flavor components or odorants in SX [3; 14] and RG [5; 7] samples, they have never been identified as unique odorants in the corresponding samples, which is consistent with our results on the secondary side. Methyl salicate and \(p\)-cymene are common aromatic VFCs in teas, which are derived from the biosynthesis of the shikimate pathway in tea plants [34; 35], and the free form of methyl salicate is released via the hydrolysis of their glycosidally bound forms under enzymatic or thermal reactions during tea processing [36]. In addition, methyl salicate has been reported to be one of the odorants in DHP, but its contribution to the overall aroma is far less than that in this study [17]. The differences in extraction and detection methods may be the main reasons for the differences. Similarly, phenethyl acetate, phenylethyl alcohol, indole, and (\(E\))-\(\beta\)-famesene were identified as the characteristic key odorants of RG, both of which presented \"floral\" or \"fruity\" scents. Among them, phenylethyl alcohol was proven to significantly influence the aroma perception of RG [5]; it was not detected in fresh tea leaves, but exhibited a growing trend in the concentrations with the promotion of RG processing, and its glycoside precursors may be heavily hydrolyzed after fermentation [6]. In addition, phenethyl acetate,  
Figure 5: Characteristic key odorants of different types of Wuyi rock teas (WRTs) ((A): Dahongpao (DHP); (B): Rougui (RG); (C): Jinfo (JF); (D): Shuixian (SX), DHP and SX, JF and RG). indole, and (_E_)-\(\beta\)-famesene have been reported as the characteristic aroma compounds of ooolong tea [13; 37], and their precursors are speculated to be phenylalanine, tryptophan, and carotenoids [38]. Linalool, phenethyl butyrate, hexyl hexanoate, and dihydroactinidiolide were identified as the key odorants of JF, with the highest concentrations and AI levels.