## 3 Results
### The Analysis of Volatile Between Different Grades of TSH  
The analysis of the volatile compounds in TSH samples showed the presence of a total of 282 kinds of components and according to the qualitative and quantitative analyses, the compounds could be clustered into ten categories listing as acids, alcohols, aldehydes, aromatics, esters, heterocyclic, hydrocarbons, ketones, N-containing compounds, and terpenoids (Figure 3A). In all grades of TSH, aromatics represented the highest proportion, range 5.11-6.23%, followed by terpenoids (2.58-3.76%), and by alcohols (2.20-2.80%). These kinds of compounds tend to contribute to the floral and fruity fragrance of processed tea, which made up for the aroma profile of TSH. Further analysis was conveyed under the PLS-DA mode combined with VIP more than (or equal to) 1 as measurement. Firstly, based on the results of PLS-DA mode (Figure 3B), four grades pf TSH could be dived and clustered into four circles. The value of PC1 (59.82%) and PC2 (13.48%) represented the reliability of this mode. Additionally, the distance between the replicates in different grades of samples was close, suggesting a reliable repeatability. TSH-0 is mostly located in the second quadrant and TSH-1 is located in the third quadrant, TSH-2 in the fourth quadrant, and TSH-3 in the first quadrant. When the measurement of VIP more than 1 (or equal to) was applied (Figure 3C), in total 108 kinds of compounds were identified (red rounds), and the green rounds represent the compounds with VIP value less than 1. Interestingly, both red and green rounds were mostly located in the first and third quadrant, while the green rounds were distributed in the center more closely, and the red rounds distributed on both ends sparsely. This loading scatter plot could reflect the distinctive components in different grades of TSH. Furthermore, to more precisely screen for differential volatiles between grades, we further refined the selection of key compounds by comparing fold change (FC) values between adjacent grades. Specifically, the sum of FC values (TSH-0 vs. TSH-1), FC (TSH-1 vs. TSH-2), and FC (TSH-2 vs. TSH-3) was calculated for 108 volatiles with VIP > 1.0. Compounds with a total FC > 3.0 were selected for analysis [34], resulting in the identification of 68 key volatiles (Table S1). Figure 3D shows the gradually dynamic change of 68 selected components in different grades of TSH. The higher grade of TSH tends to possess higher amounts of components, while the lower grade of TSH possessed a lower amount of components. As shown in Table 2, the odor character and concentration of selected key compounds are listed. Among them, the majority of selected compounds like 2,6,10-Trimethyltridecane,2-Ethylbutyric acid, tetrahydrofurfuryl ester, and 3-Isopropylidene-tricylcol[4.3.1.1(2,5)]undecan-10-one, etc. showed the highest concentration in TSH-0, which was the highest grade of TSH, approving the best aroma quality of TSH. (Z)-3-Hexen-1-ol, formate, 1-Isopropyl-3-methyl-2-pyrazoline, 6-Methyl-5-hepten-2-one, and (Z)-3-Hexenyl iso-butyrate, among others, showed significant increase trend along with the approving of grade, and all these compounds as well as (\(E\),\(Z\))-2-Butenoic acid, 3-hexenyl ester, 2,2-Dimethyl-oxazolidine,1,2,3,4,4a,7-Hexahydro-1,6-dimethyl-4-(1-methylethyl)-naphthalene, etc. were  
higher in TSH-0 and TSH-1. In summary, higher grade of TSH possessed higher amount of aroma volatile compounds, which in consistent with the sensory evaluation of TSH.