# Difference in Aroma Components of Black Teas Processed on Different Dates in the Spring Season
## 3 Results and Discussion
### Effect of Production Date on the Individual Aroma Components of Black Teas  
PCA was first performed to determine the integral differences in volatile compounds and screen the main volatile compounds distinguishing the black teas. As shown in Figure 3A, ZYQ-1 was completely separated from the other black teas in the PC2 direction,  
Figure 1: The content of different types of volatile compounds in black tea samples.  
Figure 2: The changes in flavor index of various types of volatile compounds.  
while ZYQ-2, ZYQ-3, ZYQ-4, and ZYQ-5 were successively separated from each other in the PC1 direction. To further screen the most important volatile compounds distinguishing black tea samples produced on different dates, loading plots were generated. As shown in Figure 3B, the volatile components that greatly contributed to the differences among the black teas were geraniol, methyl salicate, linalool, trans-linalool oxide, nerol, nerolidol, hexanal, phenylethyl alcohol, benzene acetaldehyde, nonanal, etc. They were all previously reported as important aroma-active compounds in black teas [8; 10; 11; 38]. It was interesting that the Group I volatiles were separated from the Group II volatiles by PC2.  
To better understand the differences in the aroma components among the black teas produced on different dates in the spring season, important differential volatile compounds were screened based on ANOVA (\(p<0.05\)) and PLS-DA (VIP \(>1\)). In total, 39 important differential volatile compounds were identified (Table 2 and Figure 4). It seemed that there were no obvious change patterns in the content of volatile compounds. However, differential volatile compounds roughly presented three distribution patterns (Figure 4). The content of (Z)-3-hexen-1-ol, nerol, (E)-\(\beta\)-ocimene, \(\delta\)-cadinene, benzyl alcohol, benzene acetaldehyde, cis-linalool oxide (furanoid), nerolidol, linalool, (E)-2-hexen-1-ol, and 1-hexanol showed an increasing trend from ZYQ-1 to ZYQ-5 and reached the maximum in ZYQ-4 or ZYQ-5. Nerol, (E)-\(\beta\)-ocimene, \(\delta\)-cadinene, benzyl alcohol, benzene acetaldehyde, cis-linalool oxide (furanoid), nerolidol, and linalool are VTs and AADVs [5] and generally present pleasant odors [36]. (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, and 1-hexanol are FADVs [5] and mainly present unpleasant odors in black teas [36]. The content of butanal, 3-methylbutanal, 2-methylbutanal, phenylethyl alcohol, cis-2-penten-1-ol, heptanal, safranal, benzaldehyde, and \(\beta\)-cyclodextrin, etc., showed a significant increase in ZYQ-5. Safranal and \(\beta\)-cyclodextrin are derived from the degradation of carotenoids [7]. The significant increase in their content resulted in the raising of the flavor index of CDVs in ZYQ-5 (Figure 2). Other volatile compounds are FADVs and AADVs [5]. (E)-2-heptenal, pentanal, methyl gernate, gerainal, cyclohexyl hexanoate, (E)-3-hexenyl butyrate, geraniol, cis-3-hexenyl hexanoate, methyl salicate, ocimene, 6-methyl-5-heptene-2-one, and longifolene showed the highest content in ZYQ-2 and ZYQ-3. Geraniol is the key odorant responsible for the characteristic aroma of Keemun black tea [10; 20], and it is the most abundant aroma component [20; 39]. In this study, geraniol was also the most abundant volatile and showed the highest content in ZYQ-2 (Table 2), which was in line with the fact that the total and VT flavor index were the highest in ZYQ-2 (Figure 2).  
Figure 3: PCA score and loading plot of black tea samples. (**A**): PCA score plot; (**B**): PCA loading plot. R\({}^{2}\)X = 0.857, Q\({}^{2}\) = 0.658. The data were Pareto-scaled.