# Effects of Five Different Withering Methods on the Composition and Quality of Congou Black Tea
## 3 Results
### Effects of Different Withering Methods on Amino Acid Composition and Content  
Amino acids can affect not only the flavor quality of tea but also the aroma of tea [22]; if phenylalanine is present, tyrosine is bitter in taste, and at the same time, it is an aromatic amino acid. During the withering process of black tea, proteins and peptides in fresh leaves undergo self-dissolution and decomposition. The speed and extent of this decomposition are related to the withering method, which results in varying compositions and proportions of amino acids, ultimately impacting the overall quality of the tea. A total of 22 amino acids (Figure 2) were detected in the five withering methods, and there was no significant difference in the amino acid species of each withering method, with the highest number of 22 species in the WAW and the lowest number of 20 species in the SHW. All the amino acids were analyzed by clustering and the results are shown in Figure 2, where all the withering methods are classified into two main groups, with the SUW treatment and SNW treatment as one group and the other withering methods as one group. There was no significant difference in the content of bitter amino acids. The process with the lowest sweet amino acid content (Figure 3A) was SHW at 1.40 mg/g, while the highest content was found in SNW at 1.79 mg/g. Among all the sweet amino acids, serine (Ser) had the highest content, with the SHW serine content (Figure 3B) being the lowest at 0.45 mg/g and the SUW content being the highest at 0.60 mg/g. There were significant differences in the total content of sweet amino acids and serine content among SHW, SNW, and SUW (\(p<0.05\)). The content of umami amino acids (Figure 3C) was lowest in SHW at 11.38 mg/g and highest in SNW at 12.70 mg/g, with a significant difference (\(p<0.05\)) between the two. A comparative analysis of the contents of all the umami amino acids revealed that the theanine content was not significantly different, whereas the glutamic acid (Glu) and aspartic acid (Asp) contents (Figure 3D) were significantly different (\(p<0.05\)), with the highest content of glutamic acid in SNW (1.52 mg/g) and the highest content of aspartic acid in NAW (0.65 mg/g). Among the five types of withering methods, the WAW amino acid type is the most abundant, whereas SNW and SUW are more conducive to the accumulation of sweet amino acids. The NAW and SNW treatments were more conducive to the accumulation of umami amino acids, whereas the SHW treatment resulted in lower levels of all the taste amino acids. [PERSON] et al. [23] reported that warm-air withering and sun withering can significantly  
Figure 1: The content of tea polyphenols (**A**), free amino acids (**B**), caffeine (**C**), and soluble sugars (**D**) in Congo black tea subjected to different withering methods (\(\%\)); different letters in the same subgraph indicate significant differences (\(p<0.05\)).  
reduce the loss of nonprotein amino acids (theanine). In this study, there was no significant difference in the theanine content among the five withering methods, and theanine content was highest in NAW, followed by WAW and SNW. This may be related to the different tea tree varieties and environmental parameters used during processing.  
Figure 3: Rose diagram of the sweet amino acid content (**A**), serine content (**B**), umami amino acid content (**C**), and glutamic acid and aspartic acid contents (**D**) under different withering methods; natural withering (NAW), warm-air withering (WAW), sun-natural combined withering (SNW), sun withering (SUW), shaking withering(SHW), serine (Ser), glutamic acid (Glu), aspartic acid (Asp).  
Figure 2: Clustering heatmap of amino acid fractions obtained via different withering methods.