# Improving the Sensory Quality of Black Tea by Blending Varieties During Processing
## 3 Results and Discussion
### Analysis of Volatile Components by GC-MS
#### 3.3.1 Multiple Statistics Analysis in Volatiles  
To explore the differences in volatile compounds of black tea samples concerning different varieties and blending methods, tea samples were analyzed by using the partial least squares discriminant analysis (PLS-DA). Before using PLS-DA, data standardization and missing value handling should be performed. As shown in Supplementary Materials Figure S6A, Fud, JX, and JGY were separated based on their volatile compounds. Similar results were also found in Fud, FJX, and FJG samples (Figure 3A), indicating that the addition of fresh leaves of oolong varieties (_Jinxuan_ and _Jinguyin_) to _Fudingdabi_ resulted in noticeable changes in the volatile compounds of black tea after processing. The permutation test with 200 iterations was used to further evaluate the performance of the PLS-DA model in the present work. It was found that lower values for R2 and Q2 in the permutated models and the intercept of the Q2 regression line were less than 0 (Figure 3B). This strongly demonstrates that the PLS-DA model is not over-fitted and reliable. Moreover, AFJX and AFJG had significant differences in volatile compounds compared to Fud (Supplementary Materials Figure S7A), while AFJG and AFJX did not present large differences from FJX and FJG (Supplementary Materials Figure S8A). Therefore, it could be confirmed that the blending of fresh leaves during processing has a similar effect on the regulation of volatiles in black tea as blending finished teas.  
Figure 3: **(A)** Partial least squares discriminant analysis score diagram (PLS\(-\)DA) of volatile compounds in the blend of fresh leaves with black tea and Fud black tea; (B) Substitution test, orange—R2, purple—Q2; (C) Differential material screening s\(-\)plot; (D) Heat map of key different substance content distribution of the blend of fresh leaves with black tea and Fud black tea.  
Potential specific volatiles in the sample of fresh leaves blended during processing were identified by using S-plots, which displayed covariance (_p_) against correlation (_p_corr) (Figure 3C). The S-plot was used to identify key volatile compounds responsible for differences in the samples, and marked as orange circles. A total of 20 volatiles were screened as specific volatile candidates among Fud, FJX, and FJG (Table 2). Linalool oxide (pyranoid) was abundant in FJG, while D-limonene had abundant content in FJX, and Fud contained a higher level of 2-methylbutanal. To further identify key aroma-active volatiles based on their contribution to the overall aroma of the tea, a cutoff of ROAV > 1 was applied [17]. As a result, 12 volatiles were excluded for not meeting the cutoff values of ROAV, leaving eight volatiles as key aroma-active volatiles distinguishing Fud, FJX, and FJG (Figure 3D, Table 2). Similarly, 14 volatiles were identified as specific volatiles among the three single varieties of the cooked samples (Fud, JX, and JGY, Supplementary Materials Table S3), while six volatiles were noted for the finished tea blended samples (Fud, AFJX, and AFJG, Supplementary Materials Table S4).