## 3 Results and Discussion
### Overall Determination of Volatile Compounds  
The tea aroma is a specific fragrance of tea formed by the combination of different aromatic substances in different concentrations on the olfactory nerve. The volatile compounds were detected and analyzed by headspace solid-phase micro-extraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) to differentiate the differences in volatile compounds among white teas. A total of 90 volatile components were identified (Table S1), classified into 9 categories (Figure 1), including sulfur, aldehydes, alcohols, ketones, acid, hydrocarbons, esters, naphthalenes, and others. The quantities of individual categories are illustrated in Figure 1.  
There were 65, 66, 58, and 63 volatile compounds identified from SH-S, FD-S, SH-A and FD-A, respectively. As shown in Table S2, the numbers of aldehydes (19, 19, 18, 18) in four groups (SH-S, FD-S, SH-A, FD-A) were highest among the categories, and the \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Biochemical Components (mg/g)** & **SH-S** & **FD-S** & **SH-A** & **FD-A** \\ \hline EC & 0.26 \(\pm\) 0.03 \({}^{\text{c}}\) & 1.66 \(\pm\) 0.02 \({}^{\text{b}}\) & 1.61 \(\pm\) 0.2 \({}^{\text{b}}\) & 2.85 \(\pm\) 0.05 \({}^{\text{a}}\) \\ ECG & 0.66 \(\pm\) 0.01 \({}^{\text{b}}\) & 0.3 \(\pm\) 0.01 \({}^{\text{b}}\) & 24.37 \(\pm\) 1.58 \({}^{\text{a}}\) & 20.44 \(\pm\) 15.17 \({}^{\text{a}}\) \\ EGC & 3.76 \(\pm\) 0.03 \({}^{\text{a}}\) & 3.9 \(\pm\) 0.09 \({}^{\text{a}}\) & 1.67 \(\pm\) 0.35 \({}^{\text{c}}\) & 2.47 \(\pm\) 0.25 \({}^{\text{b}}\) \\ EGCG & 68.48 \(\pm\) 0.49 \({}^{\text{b}}\) & 80.36 \(\pm\) 2.66 \({}^{\text{a}}\) & 67.07 \(\pm\) 2.1 \({}^{\text{b}}\) & 68.73 \(\pm\) 0.64 \({}^{\text{b}}\) \\ C & 15.58 \(\pm\) 0.37 \({}^{\text{a}}\) & 14.47 \(\pm\) 0.86 \({}^{\text{a}}\) & 18.63 \(\pm\) 0.6 \({}^{\text{a}}\) & 17.73 \(\pm\) 0.06 \({}^{\text{a}}\) \\ Caffeine & 35.52 \(\pm\) 0.5 \({}^{\text{c}}\) & 34.26 \(\pm\) 0.35 \({}^{\text{c}}\) & 47.87 \(\pm\) 1.6 \({}^{\text{a}}\) & 45.33 \(\pm\) 0.58 \({}^{\text{b}}\) \\ Free amino acid & 56.23 \(\pm\) 0.4 \({}^{\text{b}}\) & 62.37 \(\pm\) 2.05 \({}^{\text{a}}\) & 47 \(\pm\) 1.0 \({}^{\text{a}}\) & 41.67 \(\pm\) 1.15 \({}^{\text{c}}\) \\ Tea polyphenol & 159.34 \(\pm\) 4.34 \({}^{\text{b}}\) & 149.59 \(\pm\) 5.53 \({}^{\text{c}}\) & 204.33 \(\pm\) 3.06 \({}^{\text{a}}\) & 195.33 \(\pm\) 1.53 \({}^{\text{a}}\) \\ Soluble sugar & 31.86 \(\pm\) 1.89 \({}^{\text{a}}\) & 33.86 \(\pm\) 1.19 \({}^{\text{a}}\) & 22.85 \(\pm\) 1.73 \({}^{\text{c}}\) & 27.43 \(\pm\) 1.71 \({}^{\text{b}}\) \\ Water extracts content & 475.60 \(\pm\) 1.44 \({}^{\text{a}}\) & 47\(\pm\)6.47 \(\pm\) 2.37 \({}^{\text{a}}\) & 470.33 \(\pm\) 3.51 \({}^{\text{b}}\) & 471.67 \(\pm\) 1.53 \({}^{\text{ab}}\) \\ \hline \hline \end{tabular} Note: Different lowercase letters in the same line indicate a significant difference among white teas (\(p\) < 0.05). EC, epicatechir, ECG, epicatechir, EGC, epiglallocatechin; EGCG, epiglallocatechin-3 gallate; C, catechin.  
\end{table} 
Table 2: Main biochemical components of four tea groups. Figure 1: Numbers of volatile components of different categories in four groups. numbers of alcohols (11, 13, 15, 16) were second in four groups (SH-S, FD-S, SH-A, FD-A). The distribution of volatile compounds in two tea cultivars in different harvest seasons was visualized using a Venn diagram (Figure 2). Clearly, there are a total of 40 common volatile compounds between SH-S and SH-A and a total of 42 common volatile compounds between FD-S and FD-A. As depicted in Figure 3, the analysis revealed a descending order of total volatile compounds across the samples. Specifically, FD-S exhibited the highest total volatile content with 513.440 \(\pm\) 20.693 \(\upmu\)g/L (Table S1). This was followed by SH-S, with a total volatile content of 428.001 \(\pm\) 35.854 \(\upmu\)g/L (Table S1). FD-A and SH-A showed relatively low values of 352.982 \(\pm\) 23.034 \(\upmu\)g/L and 321.278 \(\pm\) 23.722 \(\upmu\)g/L (Table S1), respectively.