## 3 Results and Discussion
### Volatile Detection of Different Oolong Tea Samples  
HS-SPME-GC-MS results showed that the six oolong tea samples varied in aroma compounds. In Figure 3A,B, the total number of aroma substances are shown to be significantly higher (\(p<0.05\)) in the products of the suitable tea cultivars (MZ, HD, and TGY) than in the products of the unsuitable tea cultivars (FD, WNZ, YS). Among them, HD had a significantly higher (\(p<0.01\)) aroma level than the other cultivars, while YS showed the lowest aroma, indicating that the suitability of the oolong tea cultivars affected the total aroma. Statistical analysis of aroma compounds in different metabolic pathways [20] showed that volatile terpenes (VTs) dominated the aroma (more than 60%) in all samples, followed by fatty-acid-derived volatiles (FADVs) and amino-acid-derived volatiles (AADVs) (both over 10%), carotenoid-derived volatiles (CDVs) (about 5%), and some other unclassified substances (others). Furthermore, we compared the content data of each aroma compound in different samples (Figure 3D and Table S9). As the aroma data of each sample varied in volatile substances, based on suitability grouping, the non-parametric test (Kruskal-Wallis test) showed the clear difference between suitable and unsuitable tea cultivars (MZ, HD, and TGY versus FD, WNZ, and YS) in aroma compounds. In Figure 3D, the 64 substances are presented on the right side according to the classification of metabolic pathways, with clustering results based on the relative content of substances shown in the upper part of the heat map, which also confirms the PCoA classification results. For volatile terpenes (VTs), the two groups showed an extremely significant difference (\(p<0.01\)) in compounds, including \(\beta\)-Cimene, (Z)-Furan linalool oxide, (E)-Furan linalool oxide, linalool, (3E)-4,8-Dimethyl-1,3,7-nonatriene, Cosmene, (E)-Pyranoid linalool oxide, Linalool oxide pyranoside, \(\alpha\)-Terpineol, linalyl formate, \(\alpha\)-Cubebene, \(\gamma\)-Elemene, Humulene, (E)-\(\beta\)-Famesene, (Z,E)-\(\alpha\)-Famesene, \(\alpha\)-Muurolene, \(\alpha\)-Farnesene, T-Muurolol, and \(\alpha\)-Cadinol, and a significant difference (\(p<0.05\)) in compounds such as \(\alpha\)-Terpineol, Geraniol, \(\beta\)-Caryophyllen, \(\delta\)-Cadinene, and (E)-Nerolidol, while showing no significant difference (p \(>0.05\)) in compounds such as 1,5,7-Ocatrien-3-ol, 3,7-dimethyl, \(\gamma\)-Cadinene, Nerolidol, and (E)-2,6-Dimethyl-3,7-ocadiene-2,6-diol. Linalool and its furan oxides ((Z)-Furan linalool oxide, (E)-Furan linalool oxide) are important components of sweet and floral aromas, while (E)-Pyranoid linalool oxide and Linalool oxide pyranoside have earthy aromas [21]. Geraniol is one of the main components of the floral odor in tea [22]. (E)-Nerolidol has floral green, citrus woody, and waxy odors, which are among the characteristic aromas of oolong tea [23]. The contents of these terpenes with floral aromas are higher in the samples of suitable oolong tea cultivars, suggesting that these compounds may affect the suitability of oolong tea cultivars and play a major role in the formation of the floral aroma. With regard to amino acid derived volatiles (AADVs), the two groups showed extremely significant differences (\(p<0.01\)) in compounds including Benzaldehyde, Phenylly alcohol, Methyl salicylate, Indole, (Z)-3-Hexenyl benzoate, and Geranyl isovalerate, and a significant difference (\(p<0.05\)) inhenylacetaldehyde, while showing no significant difference (\(p>0.05\)) in compounds such as Benzyl nitrile, \(\beta\)-Phenyllythly butyrate, Benzoic acid hexyl ester, and E-2-Hexenyl benzoate. Phenylly alcohol and Phenylacetaldehyde have floral and sweet odors, Benzaldehyde has an almond odor, indole is one of the characteristic aroma substances of oolong tea [23] with a sour fruity odor, and (Z)-3-Hexenyl benzoate has a pear-like odor. These aroma compounds may contribute to the strong floral and fruity aromas in the products of suitable oolong tea cultivars.