# Effect of Fermentation Humidity on Quality of Congou Black Tea
## 3 Results and Discussion
### Effects of Fermentation Humidity on Congou Black Tea bioactivity  
The DPPH radical scavenging rate is usually used to characterize the antioxidant capacity of tea. \(\alpha\)-Amylase and \(\alpha\)-glucosidase are two essential enzymes involved in carbohydrate digestion, and by inhibiting their activities, blood sugar can be lowered, which is often used in medicine to treat diabetes [43]. The scavenging effect of DPPH free radicals and the inhibitory effects against \(\alpha\)-amylase and \(\alpha\)-glucosidase activities by black teas fermented under different humidity conditions are shown in Table 3. The half-inhibitory concentrations (IC\({}_{50}\)) indicate the concentration of the sample at 50% scavenging rate or inhibition rate, which is a key indicator for the scavenging or inhibition effect, i.e., a lower IC\({}_{50}\) value indicted a stronger scavenging or inhibitory effect of the sample. In Table 3, the DPPH scavenging effect and the inhibition of \(\alpha\)-amylase and \(\alpha\)-glucosidase activities were seen to decline significantly with the rise of fermentation humidity. Under 55-65% humidity conditions, the scavenging effect of tea on DPPH and the inhibition of \(\alpha\)-amylase and \(\alpha\)-glucosidase activities did not decrease significantly. Under 85-95% humidity conditions, except for a remarkable decrease in the inhibition of \(\alpha\)-glucosidase, the DPPH scavenging effect and the inhibition of \(\alpha\)-amylase activity also did not decrease significantly. However, there were significant differences between the high relative humidity (85-95%) and the low relative humidity (55-65%) treatments. This indicated that 75% fermentation humidity is an important turning point. The correlation between the three IC\({}_{50}\) values and the contents of taste compounds was analyzed for each sample (Figure 6). These three IC\({}_{50}\) values were all shown to have remarkable negative correlations with polyphenols, catechins (EGCG), theaflavins (TF, TFDG and four monomers of theaflavins in total) and amino acids, while having remarkable positive correlations with thearubigins, indicating that the levels of these substances in black tea can remarkably impact the bioactivity of tea samples. This correlation has been confirmed in storage experiments with white tea [44]. Among these taste components, phenolic compounds such as polyphenols, flavones, catechins and theaflavins are considered as the main and most effective antioxidants against DPPH and inhibitors of enzyme activity. The hydroxyl substituents and aromatic structure of phenolic compounds are the key factors for their antioxidant and free radical scavenging effects [45]. The hydroxyl groups in polyphenols could inhibit the \(\alpha\)-amylase activity by binding to the active site of \(\alpha\)-amylase, and phenolic compounds containing gallic acyl groups (such as catechins and theaflavins) have a greater inhibitory impact on \(\alpha\)-amylase activity due to their ability to provide abundant hydroxyl groups [46]. Similarly, hydroxylation and gallotannoylation of flavonoids in the samples could enhance their inhibitory effects on \(\alpha\)-glucosidase activity [47]. [PERSON] et al. also showed that theaflavins possess a greater ability to provide protons due to their specific structure, resulting in stronger antioxidant activity [48]. [PERSON] et al. found that theaflavins could significantly inhibit \(\alpha\)-glucosidase activity, suggesting that elevated levels of theaflavins in tea samples could significantly increase enzyme activity inhibition [5]. Amino acids with phenolic or thiohydroxyl groups (such as tyrosine, cysteine and methionine) have been shown to have stronger antioxidant activities [49]. A large proportion of common amylase inhibitors are proteins mainly derived from plants