# Analysis of the Changes in Volatile Components During the Processing of Enshi Yulu Tea
## 3 Results and Discussion
### Evolution of Differential Volatiles Throughout Enshi Yulu Taa Production  
To enhance the differentiation of aroma components during the processing stages, we used partial least squares discriminant analysis (PLS-DA). The model exhibited excellent fitting and predictive capabilities (R\({}^{2}\)X = 0.926, R\({}^{2}\)Y = 0.981, Q\({}^{2}\) = 0.951) (Figure 5A). Five sample groups were effectively distinguished based on their origin, indicating significant variations in volatile composition existed. The greatest dissimilarity was between FTL and STL samples, suggesting that the steaming process exerted a profound influence on the formation of Enshi Yulu tea's aroma. The drying process also played an important role in aroma development, while the effect of rolling was relatively minor. These findings are consistent with research on how processing techniques affect the aroma of roasted green teas [14]. To assess model robustness, we performed a permutation test with 200 repetitions for cross-validation; overfitting did not occur (Figure 5B: R\({}^{2}\) = 0.222; Q\({}^{2}\) = \(-\)0.523). To identify potential volatile component markers for the processing stages of Enshi Yulu tea, we used their VIP (Variable Importance in Projection) values in the PLS-DA model, combined with non-parametric testing (Kruskal-Wallis). A total of 100 volatile components exhibited VIP \(>\) 1 (Table S1). These volatile components varied significantly throughout the processing stages, with a distinct inflection point after steaming and drying (Figure 6). These volatile components displayed five main trends: (1) compounds such as 5-ethyl-2(5H)-furanone, 2,3,3-trimethyloctane, naphthalene, linalyl butyrate, ethyl benzoate, (\(2E\))-oct-2-enal that decreased slightly after rolling and significantly decreased during shaping and drying processes. (2) Compounds such as (\(2E\))-non-2-enal, methyl geranate, (\(3Z\),\(6Z\))-nona-3,6-dien-1-ol, 2-methylnonane, 2-methylbutyl isobutyrate, 2,6-dimethylnonane, and \(p\)-menthone that increased significantly after steaming and gradually decreased from the rolling to drying processes. (3) Compounds such as octyl acetate, 4-methyl-3-penten-2-one, octane-2,5-dione, oct-1-en-3-ol, and safranal that did not differ significantly in steaming, rolling, and shaping processes, but significantly increased during drying. (4) Compounds such as 2-ethyl-1,4-dimethylbenzene, 1-ethyl-2-methylbenzene, (\(3E\))-non-3-en-1-ol, (\(3E\))-8-methylnona-3,7-dien-2-one, 4-methylhexyl 3-methylbutanoate, 3,5,5-trimethylhexan-1-ol, 1,2,4,5-tetramethylbenzene, and heptyl butanoate that decreased significantly after steaming, remained stable after rolling and shaping and increased significantly after drying. Figure 5: PLS-DA analysis of volatile compounds in the processing stage of Enshi Yulu tea. FTL, fresh tea leaves; STL, steamed tea leaves; RTL, rolled tea leaves; SPTL, shaped tea leaves; DTL, dried tea leaves. (**A**), score plot (R\({}^{2}\)X = 0.926, R\({}^{2}\)Y = 0.981, Q\({}^{2}\) = 0.951); (**B**), Cross-validation test (R\({}^{2}\) = 0.222; Q\({}^{2}\) = \(-\)0.523). ing. (5) Compounds such as heptan-2-one, dihydro-\(\beta\)-ionone, _cis_-3-hexenyl hexanoate, 2-butyloct-2-enal, 2-phenylacetaldehyde, linalool, and phenylmethanol that decreased significantly after steaming and rolling processes but increased significantly during shaping and drying processes. Figure 6: Heat map of possible key-differential volatile components during the processing of Enshin, Yulu tea. FTL, fresh tea leaves; STL, steamed tea leaves; RTL, rolled tea leaves; SPTL, shaped tea leaves; DTL, dried tea leaves. The aroma quality of tea is significantly influenced by many components. (_2E_)-non-2-enal, an important aroma component in Longjing tea with a pleasant fragrance at low concentrations but unpleasant odor at high concentrations [26], is a major constituent in relatively higher proportions in Enshi Yulu tea (Table 2).