# Effect of Fermentation Humidity on Quality of Congou Black Tea
## 3 Results and Discussion
### Effects of Fermentation Humidity on Congou Black Tea Taste Composition  
The taste of congou black tea is related to the composition and content of its compounds, with tea polyphenols and their amino acids, oxidation products, soluble sugars and flavones as the major components to determine its flavor [2]. In Figure 3A, the content of tea polyphenols was seen to decrease with rising fermentation humidity, exhibiting highly significant differences between the low humidity samples (RH55, RH65) and the high humidity samples (RH85, RH95). A possible explanation is that the high humidity environment could enhance the activity of polyphenol oxidase (PPO) and peroxidase (POD), thus intensifying the enzymatic and other non-enzymatic reactions in the congou black tea, resulting in greater oxidation and lower retention of tea polyphenols [18]. This phenomenon was also observed in tobacco, fruits and vegetables. The higher the relative humidity of the environment, the higher the activity of PPO, and a low humidity environment can cause faster dehydration of the tobacco surface, thus reducing the activity of PPO [19]. [PERSON] et al. found that reactive oxygen species derived from a high humidity environment could stimulate the expression of PPO-related genes in mushrooms, thereby accelerating the oxidation of polyphenic compounds [20]. [PERSON] et al. suggested that a higher relative humidity environment could result in a lower actual temperature than the ambient temperature in dried banana slices, leading to greater retention of PPO and POD activity [21]. In the present study, similar trends were observed for the catechin components and their total amounts (Figure 3D). Specifically, the five treatments exhibited no obvious variations in the composition of simple catechins EGC and C. The ester catechins (EGCG, ECG) and four monomers (EGC, C, EGCG, ECG) of catechins in total showed a significant downtrend with increasing fermentation humidity, with a decrease of 42.5%, 11.8% and 14.5% from RH55 to RH95, respectively. This indicated that the sensitivity to ambient humidity was significantly greater for ester catechins than simple catechins, which is probably associated with the degradation and epimerization of catechins. As previously confirmed, the storage environment of high humidity promoted the degradation and epimerization of catechins in green tea powder [22]. The storage environment at low temperatures and humidity could significantly increase the total flavanols, total polyphenols and ascorbic acid content of green tea [23]. Ester-type catechins have stronger bitterness and astringency than simple catechins, and their higher content in the low humidity treatments may be the main reason for the higher bitterness and astringency of congou black tea [16]. Figure 2: QDA analysis diagrams for the appearance (**A**), aroma (**B**), taste (**C**) and infused leaf (**D**) of congou black tea under different fermentation humidity conditions, with different colored lines for different samples. Theaflavins are generated by the oxidative polymerization of catechins, followed by conversion to thearubigins and theabrownins [18]. As indicated by systematic analysis, with the rise of fermentation humidity, the total contents of theaflavins in tea samples gradually decreased, while the total contents of thearubigins and theabrownins gradually increased (Figure 3B-D). Among the theaflavin components determined by HPLC (Figure 3H), there was no significant change in the monomers TF-3\({}^{\prime}\)-G and TFDG of theaflavins, while TF, TF-3-G and four monomers (TF, TF-3-G, TF-3\({}^{\prime}\)-G, TFDG) of theaflavins in total all showed a significant downtrend. Theaflavins are the main components of the brightness and golden ring appearance of a tea infusion, and also determine the umami and astringency of a tea infusion [24].