# 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
Consequently, during the rolling process, enzymatic reactions cannot generate aroma components, and thermodynamic reactions also fail to produce these compounds; only volatilization of existing aroma components occurs, causing a slight reduction in their abundance. Aroma components typically have low volatility at ambient temperature, leading to a minor decrease. After shaping, the up-regulated TDCs included dihydro-\(\beta\)-ionone, \(\beta\)-ionone-5,6-epoxide, phenylmethanol, 1-(1H-pyrrol-2-yl)-ethanoneone, cyclohexanone and others. Down-regulated TDCs included methyl geranate, nervibobutyrate, (_Z_, _E_)-\(\alpha\)-farnesene, undecylenic acid, (_Z_)-3-hexenyl acetate, (_2E_)-dodec-2-en-1-ol, 2,3-dihydro-1H-indol-2-one, linac aldehyde C and others. (Figure 4C). Down-regulated TDCs were significantly higher than the up-regulated TDCs, irrespective of the extent or magnitude of change, suggesting that the shaping process exerted a comparable impact to steaming on the aroma of Enshi Yulu tea During production, the shaping process of Enshi Yulu tea usually occurs at approximately 100 \({}^{\circ}\)C--a temperature at which many aroma components volatilize, leading to a decrease in their contents (Figure 4C). However, high temperatures can promote the degradation of carotenoids into \(\beta\)-ionone, geranylacetone, 5,6-epoxy-\(\beta\)-ionone, and other aroma components [36]. Sugars and amino acids also generate heterocyclic aroma components through the Maillard reaction [20]. In up-regulated TDCs, \(\beta\)-ionone-5,6-epoxide, and dihydro \(\beta\)-ionone are volatile products of carotenoid degradation [39]. 1-(1H-pyrrol-2-yl)-ethanoneone is a product of the Maillard reaction [20]. Figure 3: Numbers of differential volatiles in the processing stages Enshi Yulu tea. FTL, fresh tea leaves; STL, steamed tea leaves; RTL, rolled tea leaves; SPTL, shaped tea leaves; DTL, dried tea leaves. After drying, the up-regulated TDCs include 4-methyl-3-penten-2-one, 2-methyl-pentadecane, oct-1-en-3-ol, tetradecane, isopinocamphool, octane-2,5-dione, _cis_-8-hydroxy-linalool, dec-1-en-3-one, and cyclopentyl butyrate. Down-regulated TDCs comprise ethylbenzene, linalyl butyrate, ethenylbenzene, and \(\beta\)-cedrene (Figure 4D). The magnitude of change in down-regulated TDCs is greater than up-regulated ones in both quantity and change factor--an observation consistent with a significant increase in total aroma after drying (Figure 2). Despite similar high-temperature conditions in the shaping and drying processes under identical processing technology for Enshi Yulu tea production, the compounds' alteration trends after drying are essentially opposite to those observed during the shaping process, with evident differences in TDCs. These findings indicate that the effects of shaping and drying on aroma formation in Enshi Yulu tea differ. Although both processes occur subsequent to the fixing step and involve only thermodynamic actions, the water content differs between them: during shaping, the tea's moisture content must be reduced from approximately 65% to 25%, and during the drying process, it is further decreased to \(<\)6%. The moisture content of tea leaves is greater during shaping, favoring moist heat reactions, and lower during drying, which may promote dry heat reactions instead. Water plays an important role in product formation through the Maillard reaction within the glucose-glycine/proline/lysine model system [40] and degradation  
Figure 4: Bar chart of differential compounds in the processing stages of Enshi Yulu tea: **(A)** STL vs. FTL, **(B)** RTL vs. STL, **(C)** SPTL vs. RTL, and **(D)** DTL vs. SPTL. Orange: up-regulated compounds; Green: down-regulated compounds. The number above the column means fold change. FTL, fresh tea leaves; STL, steamed tea leaves; RTL, rolled tea leaves; SPTL, shaped tea leaves; DTL, dried tea leaves. of carotenoids leading to aroma component generation [36; 41].