# Improving the Sensory Quality of Black Tea by Blending Varieties During Processing
## 3 Results and Discussion
### Analysis of the Main Taste Compounds
#### 3.2.1 Analysis of Catechins and Relevant Compounds  
Catechins are the main polyphenic compounds found in tea and play important roles in determining the taste of black tea. Catechins can be classified based on their structure into two categories: non-ester catechins (C, EC, GC, EGC) and ester catechins (CG, ECG, GCG, EGCG) [22]. It was reported that ester catechins contribute to strong bitterness and astringency, while non-easter catechins provide a pleasant aftertaste in tea infusion [7]. In a comparative analysis, it was found that the content of ester catechins was highest in JGY, while the lowest levels of non-ester catechins were observed in JX (Supplementary Materials Figure S2A). When fresh tea leaves from _Fudingdabai_ were blended with the  
Figure 1: The scores of sensory evaluation results of three single varieties and different blending methods: (**A**) Comparison of sensory scores of black tea processed by Fud, JGY, and JX; (**B**) Comparison of sensory scores of black tea processed by Fud, FJG, and FJX; (**C**) Comparison of sensory scores of black tea processed by Fud, AFJG, and AFJX; (**D**) Comparison of sensory scores of black tea processed by FJG, FJX, AFJG, and AFJX. _Jinxuan_ variety, the contents of both ester-type catechins and non-ester catechins were significantly decreased (\(p<0.05\)) in FJX (Figure 2A). However, the content of ester catechins increased in FJG while non-ester catechins decreased (Figure 2A). The increase in ester catechins in FJG and the decrease in FJX may be due to the higher content of ester-type catechins in JGY. Although the ester-type catechins in JX are higher than in Fud, after blending fresh leaves from different varieties, changes occur in the catechin content and ratio in the fresh leaves, as well as in the activities of PPO and POD, which promote the conversion of ester-type catechins into theflavins in FJX [23]. The change in ester catechins between FJX and Fud was attributed to a significant decrease (\(p<0.05\)) in the content of EGCG due to the addition of fresh _Jinxuan_ leaves (Figure 2A). The high activity levels of polyphenol oxidase and peroxidase in fresh _Jinxuan_ leaves led to the degradation of EGCG when blended with Fud [24]. In FJG samples, the increase in ester catechins corresponded with higher levels of ECG and EGCG, while the decrease in non-ester catechins was associated with declines in GC and C. Finished tea blending samples (AFJX and AFJG) presented relatively high levels of ester catechins (Supplementary Materials Figure S3A) compared to Fud, attributable to the addition of JX and JGY, which have high catechin contents. The ratio of ester catechins to non-ester catechins serves as an indicator of the strength of the tea infusion [25]. Therefore, blending treatments can adjust both the content and ratio of catechins, thereby affecting the strength of tea infusion. The difference is that blending fresh leaves involves complex biochemistry reactions, while blending finished tea is connected to the combination of the samples used. Theaflavin is a key component used as a quality parameter in black tea [7]. It has an orange-red color and contributes briskness, strength, and brightness to black tea infusion [14]. The levels of theaflavin monomer contents in the JGY and JX samples were significantly higher than Fud (\(p<0.05\)) (Supplementary Materials Figure S2A), indicating that oolong tea varieties have advantages in the formation of theaflavin during black tea processing. This may be due to the fact that different varieties determine the differences in the expression of polyphenol oxidase and peroxidase genes, leading to varying activation abilities of these enzymes during the tea processing [24], and that the blending of fresh leaves from two varieties causes changes in the expression of enzyme genes, promoting the conversion of catechins into theaflavins [26], which is consistent with the aforementioned research.