# Effects of Five Different Withering Methods on the Composition and Quality of Congou Black Tea
## 4 Discussion  
This study conducted a comprehensive and systematic analysis of five different withering methods for Congou black tea, revealing the impact of different withering methods on its internal components. In previous studies, [PERSON] et al. [33] compared the effects of sun withering, natural withering, and warm-air withering on the quality of Qimen black tea. The research results revealed that sun-withered tea had high levels of polyphenols and soluble sugars, but low levels of free amino acids, which is consistent with the results of this study. Sun withering is the process in which fresh leaves lose water under sunlight, during which both the respiration of fresh leaves occurs and also intense photosynthesis takes place. Research by [PERSON] et al. [34] has shown that sunlight withering promotes carbon metabolism in withered leaves and inhibits nitrogen metabolism. In withered tea leaves subjected to sunlight, the synthesis and breakdown of catechins, as well as the synthesis and consumption of soluble sugars, are quite intense. These findings may explain the high content of catechins and soluble sugars in tea leaves subjected to sunlight withering and the low content of free amino acids. Although the tea polyphenols may be low, their individual catechin components are high. Perhaps this is because warm-air withering significantly upregulates differentially expressed genes (DEGs) related to catechin, resulting in an increase in catechin concentration [23]. Among the five withering treatments, SHW had the highest contents of aldehyde and ketone aroma compounds, including benzaldehyde, phenylacetaldehyde, nonanal, furfural, 2-heptanone, 3-undecen-2-one, and acetophenone, which were significantly different from those of the other four treatments. SHW had the lowest content of linalool, while the content of linalool isomers such as geraniol was the highest and significantly different from those of the other four treatments. Shaking promotes cell rupture, allowing the precursors of aroma compounds to mix with enzymes and undergo enzymatic reactions. It is also associated with the oxidation of catechins during the process. The coupled oxidation of quinones promotes the formation of aldehydes, ketones, and the oxidation of linalool, which is consistent with the findings of [PERSON] et al. [34] and [PERSON] et al. [35]. Compared to other withering methods, natural withering with long and moderate water loss is conducive to the full transformation of internal components. It has higher levels of free amino acids and soluble sugars. Although it has higher levels of tea polyphenols, the bitterness of caffeine is the lowest. It also has a higher ratio of TFs and TRs to TBs, which may be the reason why NAW treatment has superior sensory evaluation. Owing to the fact that this study only examined dried samples and lacked a dynamic study on the effects of different withering methods on the quality of Congou black tea, the next step of this study will involve the use of metabolomics techniques to analyze fresh tea leaves, withered tea leaves, and dried tea to explore the dynamic changes in the components of Congou black tea resulting from different withering methods. It is hoped that through the above research, necessary data support will be provided for the optimization and adjustment of the processing parameters of Congou black tea in the future.