# Analysis of the Changes in Volatile Components During the Processing of Enshi Yulu Tea
## 3 Results and Discussion
### Effects of Processing Steps on Volatile Components  
To better understand the impact of processing steps on volatile components, we screened differential compounds (\(p\) < 0.01) with a fold change \(\geq\) 1.50 (up-regulated) or \(\leq\)0.67 (down-regulated) at each stage. The most pronounced variations in aroma components occurred during the steaming process (Figure 3, Table S2), where the contents of 159 volatile components changed significantly (20 up-regulated, 139 down-regulated). Only 24 distinct compounds differed during the rolling process, and all were down-regulated. Following shaping, there were notable changes in 106 volatile components, of which 60 were up-regulated and 51 were down-regulated. Drying led to significant modifications in 76 volatile components, of which 67 were up-regulated, and 13 were down-regulated. The high number of differential volatile components after green tea steaming further confirms the importance of this step in determining green tea quality. Shaping and drying processes also exert considerable influence on the aroma of Enshi Yulu tea. To better understand the influence of the way that processing methods affect volatile components, we performed extensive screening and comparison of differential compounds (TDCs) that most significantly varied at each processing stage (Figure 4). After steaming, up-regulated TDCs comprised compounds such as 9-methyl-1-undecene, (_2E_)-non-2-enal, \(p\)-menthone, (_3Z_,_6Z_)-non-3,6-dien-1-ol, and (_5E_)-2,6-dimethylocta-5,7-dien-2-ol. These compounds exhibited a wide range of multiplicities ranging from 2.74 to 38.34 (Figure 4A). Conversely, down-regulated TDCs included _cis_-jasmone, 4,8-dimethyl-1,7-nonadiene, \(\alpha\)-thujamenthone, _cis_-3-hexenyl butyrate, terpinen-4-ol, 3-methylbutyl formate, oct-1-ene, \(\beta\)-citronello, \(p\)-mentha-8-en-3-one, and isoitalicene, with a decline rate up to approximately 12.49 times (_cis_-jasmone) (Figure 4A). During steaming, the degradation of fatty acids and carotenoids into aroma components is facilitated by both thermodynamic action at high temperatures and enzymatic activity prior to enzyme inactivation [36; 37]. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Compounds** & **Proportion (\%)** & **Odor Characteristic** & **Compounds** & **Proportion (\%)** & **Odor Characteristic** \\ \hline  & linaolol & 12.35 & floral * & (_3Z_)-hex-3-en-1-ol & 1.01 & fragrant, grassy * \\  & geraamid & 7.41 & floral, sweet * & 2.3-dimethylhexane & 0.94 & \\  & & & & 3.36-trimethylhept-1-5, & 0.94 &Moreover, sugars and amino acids undergo the Maillard reaction, leading to the generation of heterocyclic aroma components [20]. However, elevated temperatures can also cause substantial volatilization of aroma components. Additionally, during the fixing process, alcohol-based aroma components can combine with glucose and primrose sugar to form glycosidically bound volatiles [38], which inevitably reduces the contents of alcohol-based aroma components. Variation in molecular weight and polarity of aroma components produces different volatility levels. During the steaming process, the volatilization rate may exceed the replenishment rate for most aroma components, with few exhibiting the opposite trend. Consequently, most aroma components decrease considerably following steaming, while a few, such as (_2E_)-non-2-enal and (_3Z_,_6Z_)-non-3,6-dien-1-ol, increase. After rolling, including methyl geranate, di-epi-1, 10-cubenol, 1H-indole, \(\beta\)-cedrene, carveol, linalyl butyrate, and (_3E_,_5E_)-octa-3,5-dien-2-one were down-regulated (Figure 4B). Compared with the steaming process, the range of variation in volatiles after rolling was lower--an observation consistent with changes in the total amount of aroma components (Figure 2). It is customary to allow Enshui Tea to cool to ambient temperature before rolling it to preserve its green color and inhibit enzyme activity.