## 3 Results
### Qualitative and Quantitative Analyses of Common Aroma Components in All Black Tea Samples
#### 3.3.2. PCA and PLS-DA Analyses for the Potential Key Compounds (VIP)  
Principal Component Analysis (PCA) is a multivariate statistical method that converts multiple indicators into a few unrelated comprehensive dimensions and classifies the comprehensive indicators according to certain rules. Here, we used PCA to reveal relevant differences between JBT and FBT based on the content of compounds. As shown in Figure 4, the data could be represented according to the main components, PC1(51.9%) and PC2 (23%), which represent 74.9% of the total variance. This value allows us to describe the JBT and FBT characteristics in a reliable way. Additionally, the distance between the replicates of different samples was close, suggesting reliable repeatability. Ten kinds of JBT could be clustered into one group as class 1 (Figure 4A, orange circle), while three kinds of FBT were clustered as class 2 (Figure 4A, green circle). The various colors represent the different tea samples. This separation indicates that both tea types were highly differentiable. The loading scatter plot (Figure 4B) showed that indole, trans-linalo oxide (furanoid), teriponle, dihydromycenol, (2-methylpropyl)-pyrazine, \(\delta\)-decalactone, and 7-Oxabicyclo[4.1.0]heptan-2-one, 6-methyl-3-(1-methylethyl) had higher values according to  
Figure 3. The aroma profile of JBT and FBT. Different colors correspond to the nine compound categories identified in GC-MS. JBT 1–10 indicates the sample number of Jinmudan black tea, and FBT 1–3 indicates the sample number of Fuyun black tea. PC1, which reflects the distinctive compound contents of JBT. Meanwhile, 2-Methyl-7-exovinylbicyclo[4.2.0]oct-1(2)-ene and 1-(2-pyridinyl)-ethanone had higher values according to PC2, which reflects that these compounds may be relevant in FBT. Thus, the PCA analysis was able to reveal the characteristic compounds of JBT and FBT. Further investigation of PLS-DA (Partial Least-Squares Discriminant Analysis) was applied to distinguish the characteristic aroma compounds of JBT and FBT, and simultaneously, a VIP (Variable Importance Projection) score higher than (besides equal to) 3 was used as a screening criterion. Table 3 shows that in JBT, seven kinds of compounds were identified in total. Among these, indole had the highest VIP value (7.21), followed by methyl salicate (6.45) and \(\delta\)-decalactone (4.30), which suggests that they are key potential aromatic compounds and even contributed considerably to the peach-like aroma. Interestingly, it is noteworthy that \(\delta\)-decalactone is also the characteristic aromatic compound of peach fruit. Figure 4: The result of the PCA analysis that was performed on JBT and FBT characteristics. (**A**) The orange circle covers the JBT 1–10, which belongs to class 1 and the green circle covers the FBT 1–3, which belongs to class 2. The contribution rate of the first principal component was 51.9%, and the second principal component was 23%. (**B**) The loading scatter plot of PCA analysis. The orange stars represent the advantageous compounds according to PC1, while the green stars represent the advantageous compounds according to PC2. Applying the same kind of analysis to FBT showed lower amounts of floral and fruity aroma compounds, which is similar to the sensory evaluation results showing that FBT has basically a caramel-like aroma. A total of six kinds of compounds had a VIP score higher than (besides equal to) 3 in FBT (Table 4). Methyl salicate had the highest score (6.83), followed by 1-(2-pyridinyl)-ethanoneone(4.31), which has a nutty and popcorn-like aroma, and by 2H-pyran-2-one,tetrahydro-6-methyl(4.05), which has a burn-like aroma. Methyl1 salicate thus plays an important role both in JBT and FBT, as well as in other processed teas such as white tea [28] and oolong tea [29]. This compound also contributes to the clean and fresh fragrance. In conclusion, our analyses allowed the identification of several compounds as characteristic components of JBT and FBT aroma.