## 3 Results and Discussion  
### Dynamic Alterations during Processing Analyzed via GC-E-Nose  
As a pioneering electronic sensing methodology, the GC-E-Nose is capable of executing real-time online surveillance of volatile fingerprint changes. The typical logarithmic radar diagrams of SFABT within the final firing processing acquired from the MXT-5 and MXT-1701 columns are shown in Figure S1. Each peak corresponds to a specific volatile compound, with the peak area correlated with the volatile content.  
To gain insight into the dynamic alterations in volatile fingerprints of SFABT throughout the manufacturing process, PLS-DA was employed as an effective multivariate statistical technique. As a supervised classification analysis method, PLS-DA possesses the capability to distinguish observations across groups and can pinpoint the influential variables contributing to the disparities by appropriately rotating the principal components. The model parameters (R\({}^{2}\)Y = 0.963, Q\({}^{2}\) = 0.869) suggested an excellent fit with high predictive power (Figure 1A). To scrutinize the robustness of the model, a total of 200 iterations of the permutation test were carried out. No over-fitting phenomena were observed, with the model parameters as follows: R\({}^{2}\) = 0.357 and Q\({}^{2}\) = \(-\)0.626 (Figure 1B). The PLS-DA score shows that the volatile fingerprints of SFABT were in constant dynamic change during the whole process. Notably, considerable fluctuations emerged in volatiles within the stages of shaking, rolling, and final firing, primarily during the processes of shaking and rolling. [PERSON] et al. addressed the effects of shaking on the evolutionary mechanisms of volatile metabolites of black tea and found that shaking could stimulate the oxidative degradation of fatty acids and carotenoids to promote the formation of floral/fruity volatile metabolites [24]. Rolling, a critical step in the formation of SFABT, destroys leaf cells and ensures the uniform maceration of tea leaves, prompting aroma precursors to precipitate into the cells. These substances subsequently endure enzymatic oxidation, yielding the generation of numerous volatile substances [23; 25; 26]. In addition, scanning electron microscopy was implemented to further observe the mechanism of dynamic change in the microstructure. The results show that the leaf epidermis gradually appeared to fold after the withering and shaking processes. The leaf tissue was seriously damaged during the rolling stage (Figure S2), which further confirms the above phenomenon. In addition, [PERSON] et al. (2019) [27] investigated the dynamic alterations of chemical compositions in black tea during processing and discovered that the most notable disparities occurred in the withering and rolling stages, which is consistent with our results. In conclusion, the results show that the fingerprint changes of SFABT could be quickly and effectively characterized by the GC-E-Nose.  
Figure 1: PLS-DA of SFABT over the entire manufacturing process via the GC-E-Nose. **(A)** Scores of PLS-DA (R\({}^{2}\)Y = 0.963 and Q\({}^{2}\) = 0.869). **(B)** Cross-validation by a 200-fold permutation test (R\({}^{2}\) = 0.357 and Q\({}^{2}\) = \(-\)0.626).