## 3 Results and Discussion  
### Volatile Flavor Compounds  
Aroma is an important factor used to evaluate the quality of tea products, with different processing methods having significant effects on tea aroma. The volatile flavor of _P. chintense_ leaves and their tea products were analyzed, and the results are shown in Figures 1A and S1 and Table S1. In UL, 63 unique volatile flavor compounds were identified, comprising 12 alcohols, 11 aldehydes, 13 esters, 5 acids, 8 ketones, 8 hydrocarbons, 3 oxocycles, and 3 other substances. In GTL, 56 volatile flavor compounds were identified, comprising 12 alcohols, 16 aldehydes, 9 esters, 6 acids, 5 ketones, 3 hydrocarbons, 3 oxocycles, and 2 other substances. In BTL, 56 volatile flavor compounds were identified, comprising 12 alcohols, 16 aldehydes, 10 esters, 3 acids, 7 ketones, 3 hydrocarbons, 4 oxocycles, and 1 other substance. Alcohols, aldehydes, and esters were the main volatile compounds found in _P. chintense_ and its products, similar to Kombucha tea [15]. The total number of flavor substances in UL was more than that of BTL or GTL. Butyrolactone; ammonium acetate; bicyclo[2.2.1]heptan-2-one; terpinen-4-ol; benzoic acid, methyl ester; thujone; hexadecanoic acid, ethyl ester; benzeneacetic acid, ethyl ester; and tetradecanoic acid, ethyl ester were only found in UL (Figure 2) and could be the representative flavor substances of _P. chinense_ leaves. Among them, thujone is a volatile monoterpene ketone of traditional medicinal plants and a \(\gamma\)-aminobutyric acid regulator [16]. For tea products, high-temperature roasting or fermenting is an important processing stage used to create new flavor substances. BTL formed by fermented tea processing contained slightly lower amounts of volatile flavor substances than GTL formed through non-fermentation tea processing. BTL had a higher aroma concentration than GTL due to its complex processing method [17]. These substances were further fermented during fermentation, resulting in the production of more flavor substances, such as 2-pentanone, formic acid, butyl ester, 1-hexanol, 2-hexen-1-ol, 1-penten-3-one, and _cis_-3-hexenyl _cis_-3-hexenoate. Therefore, fermentation could improve the quality and quantity of volatile flavor components, as related to the study by [PERSON] [PERSON] and [PERSON] [18]. PCA score analysis showed that the nine samples divided into UL, GTL, and BTL were clustered well (Figure 1B), with PC1 and PC2 accounting for 50.9% and 22.9% of the total variance, respectively, and with PC1 and PC2 combined accounting for 73.8% of the total variance. The improved classification was likely due to differences in the volatile flavor level related to the processing method [17]. PLS-DA was used to investigate the distribution differences of volatile components between the different samples. The PLS-DA score plot (R2: 0.893, Q2: 0.758) demonstrated that UL, GTL, and BTL were well discriminated by the volatile metabolites identified. Among the compounds identified, 43 volatile compounds were selected as key differential markers in the PLS-DA model with a threshold of 1.0 and \(p\)-values less than 0.05 [19], which contributed significantly to the aroma of the constituents in _P. chinense_ leaves and their tea products. [PERSON] et al. [20] analyzed the flavor substances of black, green, and white tea. From a total of 46 detected flavor substances, it was suggested that phenylethanol, decanol, octanoic acid, ethyl octanoate, and ethyl decanoate could be used as the representative flavor substances of Kombucha tea. Clustering heat map analysis was subsequently used to provide detailed information  
Figure 1: Volatile components of _P. chinense_ leaves (UL), _P. chinense_ leaves green tea (GTL) and _P. chinense_ leaves black tea (BTL). (**A**) The number and composition of the volatile flavor substances in UL, GTL, and BTL. (**B**) Principal component analysis (PCA) score plot for volatile metabolites. (**C**) Partial least squares discriminant analysis (PLS-DA) score plot for volatile metabolites.