## 3 Results and Discussion  
### Alterations of Phytochemical Compositions of Green and Black Tea after the Decaffeination  
#### 3.1.1 Non-Volatile Components  
The green tea (GT) and black tea (BT) were made from the same fresh leaves. After their different processing procedure, the TWSS, total phenolics, and TFAAs of GT were significantly higher than that of BT (Figure 1A-C). However, the difference in caffeine content in these two samples was not significant, indicating that the effects of their processing procedures on caffeine do not significantly differ. These two samples were decaffeinated using the SCD method. The caffeine in GT and BT were dramatically reduced by 98.2 and 97.1%, respectively (Figure 1D). Although it's effective for decaffeinating tea, the supercritical CO\({}_{2}\) extraction method may remove other tea components and then affect the tea's sensory \begin{table}
\begin{tabular}{c c} \hline \hline
**Time (min)** & **Temperature (\({}^{\circ}\)C)** \\ \hline
0 & 40 \\
15 & 100 \\
17 & 100 \\
27 & 120 \\
31 & 120 \\
55 & 180 \\
57 & 180 \\
59.5 & 230 \\
61.5 & 230 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The chromatographic conditions of volatiles. qualities. In decaffeinated green tea (DeCAF-GT), the TWSS, TFAAs, and total phenolics were significantly lower than that in GT. However, the TWSS and total phenolics in BT and decaffeinated black tea (DeCAF-BT) were not significantly changed. In addition, the DeCAF-BT contained more TFAAs than that in BT. For the GT and DeCAF-GT, there were no significant differences in the contents of theaflavins, thearubigins, and theabrownins (Figure 2A). Compared with the BT, the decaffeinating technology led to higher theaflavins, higher thearubigins, and lower theabrownins in the DeCAF-BT. The polarity of thearubigins and theabrownins is not known, because of the lack of their exact chemical structure. However, it is clear that caffeine is more polar than theaflavins. Therefore, the solubility of theaflavins is lower than that of caffeine in a supercritical CO\({}_{2}\) system with water as the co-solvent, and it has also been found in previous studies that the extraction rates of theaflavins, thearubigins, and theabrownins are considerably lower than those of caffeine in the same system [24]. Therefore, in this study, the loss of theaflavins, thearubigins, and theabrownins during the SCD should be considerably lower than that of caffeine. Although the degradation of theabrownins leads to the formation of theaflavins, thearubigins, and other components under high temperature and pressure are not clear, it's believed that theabrownins are formed by polymerization of catechins, theaflavins, thearubigins, and others (e.g., polysaccharides and proteins) [25]. The higher theaflavins, higher thearubigins, and lower theabrownins in the DeCAF-BT may be contributed to the degradations of theabrownins under high temperature and pressure during the decaffeination processing, given that the degradation of theabrownins occurs under high temperature [26]. In addition, the total phenolics and TFAAs of DeCAF-BT were not lower than that of BT, which may be contributed to the degradation of theabrownins during the decaffeination processing. Meanwhile, after the SCD, the total weight of BT is reduced, which further contributes to an increase in the proportion of some substances (e.g., TFAAs, thearubigins, and theabrownins) in the tea leaves. Together, these may have contributed to the fact that the TFAAs and total phenolics in the DeCAF-BT were not significantly lower than that in the BT. However, it still needs further study to investigate why the TWSS was not significantly changed in DeCAF-BT. Phenolics and caffeine contribute to the bitterness and astringency of tea, and amino acids exhibit umami in tea [27]. For the BT, theaflavins, thearubigins, and theabrownins contribute to the characteristic flavor and color [28; 29].