## 3 Results and Discussion
### Comparative Analysis of HS-GC-IMS and HS-SPME-GC-MS in Identifying VOCs
#### 3.4.2 PCA of All VOCs  
In order to comprehensively evaluate the discriminative capacity of the two analytical methods applied to the four sample groups, as well as to elucidate the VOCs most strongly correlated with each group, unsupervised PCA analyses were conducted on both datasets, as depicted in Figure 5A,B. Figure 5A illustrates the PCA score plot (Figure 5A(a)) and the corresponding bi-plot (Figure 5A(b)) based on VOC concentration data obtained via HS-GC-IMS. The first two principal components account for 81.8% of the total variance, effectively segregating the four sample groups into distinct quadrants. Control groups are primarily located along the positive axis of PC1, whereas drought-stressed groups occupy the negative axis of PC1. Similarly, WNZ cultivars are positioned on the positive side of PC2, and FD cultivars on the negative side. The above results indicate that both tea cultivars experienced drought stress-induced significant variations in volatile profiles. Furthermore, Figure 5A(b) identifies several key VOCs strongly associated with WNZ-CK, including 2-pentyl furan (fruity and green), linalool-M (citrus and floral), 2-ethyl furan (Beany, ethereal, and cocoa), (E)-2-pentenal (green and fruity), (E,E)-2,4-Hexadienal (sweet and green), and octanal (waxy and citrus). Collectively, these compounds contribute to the characteristic green, fruity, and citrus aroma of WNZ-CK. In contrast, WNZ-D, situated in the second quadrant, is closely associated with 2-pentanone (sweet, and fruity), (E)-2-hexenyl acetate-D (sweet privet), benzaldehyde-D (bitter, almond, cherry, and burnt sugar), (E)-2-hexenyl acetate-M (sweet privet), oct-1-en-3-ol (mushroom, earthy, and green), and methyl acetate (sweet and fruity), contributing sweet, fruity, and earthy notes to the aroma profile of WNZ-D. In parallel, FD-D exhibits a strong correlation with VOCs such as 2-butanone (fruity, and camphoraceous), acetone (apple and pear), tetrahydrofuran, 5-methylfurfurral (sweet and caramellic), and 2-furanmethanol, 5-methyl- (sweet and caramellic), which collectively imbue FD-D with distinctive fruity, sweet, and caramel-like aromas. On the other hand, FD-CK is highly correlated with (E)-2-hexenal (leafy, green), ethylpyrazine (nutty and coffee), (E)-2-enal, (E)-hept-2-enal-M (green, vegetable), and (E)-2-hexen-1-ol (fresh green and leafy), lending a predominantly leafy, green, and nutty aromatic profile to FD-CK. Figure 5: PCA plot and bioplot HS-GC-IMS and HS-SPME-GC-MS. **(A)** PCA **(a)** and biplot **(b)** of VOC intensity detected by HS-GC-IMS; **(B)** PCA **(a)** and biplot **(b)** of VOC concentration detected by HS-SPME-GC-MS. Figure 5B illustrates the PCA of VOCs in the four sample groups, as determined by HS-SPME-GC-MS. PC1 and PC2 explain 36.9% and 27.8% of the total variance, respectively. The sample groups are distributed across three quadrants, demonstrating clear discrimination between the control and drought-stressed groups. FD-CK and WNZ-CK are both situated in the first quadrant, while FD-D occupies the second quadrant, and WNZ-D the fourth quadrant (Figure 5B(a)). Notably, PC1 effectively separates the control and treatment groups of the FD cultivar, while PC2 discriminates between the control and treatment groups of the WNZ cultivar. Although FD-CK and WNZ-CK both reside within the first quadrant, their confidence ellipses differ, with FD-CK falling within the 50% confidence interval and WNZ-CK within the 75% confidence interval. Compared to the HS-GC-IMS results, the HS-SPME-GC-MS analysis reveals a broader range of VOCs (Figure 5B(b)). The results from Figure 5I and Figure 5(Bb) illustrate that VOCs highly correlated with the control groups (WNZ-CK and FD-CK) are predominantly linked to floral, herbal, green, and fruity aroma characteristics.