## 3 Results and Discussion
### Dynamic Changes during Processing Analyzed via GC-IMS
#### 3.2.2 Qualitative Results of Volatile Components during SFABT Processing  
In this study, a comprehensive analysis unearthed a total of 100 signal peaks, out of which 59 recognizable typical target volatiles emerged (Table S2). The predominant compounds within these groupings included 11 alcohols, 1 sulfide, 13 aldehydes, 3 terpenes, 12 ketones, 6 heterocycles, and 13 esters. Nevertheless, there remained 23 peaks that failed to receive identification. Certain individual compounds may generate multiple signals or spots (such as dimers and even trimers), which could potentially be ascribed to their different contents [28]. Notably, the drift time of dimers was greater because of their proton affinities and elevated contents.  
Although the topographic plots showed tendencies of the volatile compounds, accurate judgment regarding specific components was challenging. The fingerprint is an effective way of addressing this problem, where each row depicts the complete signal peak of a single sample, and each column denotes the identical components across disparate samples. The content is signified by the color code of the square--the brighter the color, the higher the content. Known components are denoted with their existing names, whereas unidentified components are labeled with numbers. As depicted in Figure 3A, there was an appreciable enrichment in the contents of pentan-1-ol monomer (#68), benzaldehyde dimer (#21), and ethylsulfide (#80) in fresh leaves, as compared to their concentrations in the remaining processed stages. In the withering stage, the concentration levels of 2-heptanone (#31, #35), 2-methyl-1-propanol (#82), \(n\)-hexanol (#97), 2-methylbutanan-1-ol monomer (#92), 3-methylbutanan-1-ol dimer (#79), methyl valerate (#77), 2-methyl-2-pentan (#76, #81), and butanoic acid, 2-ethyl-3-methyl, ethyl ester dimer (#15) exceeded those in the other stages. The contents of methyl acetate (#66), butanal (#64), 3-pentanone (#83), octanal (#42), 2-butoxyethanol (#32), _cis_-linalo oxide dimer (#8), and _trans_-linalo oxide (#4, #5) were clearly enhanced in the shaking stage, albeit being relatively lower in the initial two stages. Their contents tended to decrease in subsequent stages. Concerning rolling, esters such as butyl acetate (#89, #100), methyl butyrate (#84, #88), methyl 3-methylbutanoate (#87), ethyl hexanoate (#44), and hexyl formate dimer (#24) were observed to be elevated in the rolling stage compared to the other processed samples. Significantly elevated levels of tert-butanol (#96), (_E_)-hept-2-enal (#33), 2-acetylfuran (#29), \(\alpha\)-fenchene (#27), ethyl 3-hydroxybutanoate (#22), \(\alpha\)-phellandrene (#19), 2-pentyl furan (#17), (_E_)-2,4-heptadien(#12), \(\gamma\)-terpinene (#9), and methyl salicate (#2) were observed during the fermentation process. Regarding the first drying stage, aldehyde compounds such as pentanal (#57, #58), heptanal (#25, #26), nonanal (#45), hexanal (#49, #50), and (_E_)-2-pentenal (#52, #53) were found to be more abundant in the first drying stage than in the other processed samples. It is hypothesized that the heating process could potentially enhance the degradation of fatty acids, subsequently generating the associated fatty aldehyde. For the final firing process, the contents of (_E_)-3-penten-2-one (#73), 3-hydroxybutanan-2-one (#71), dihydro-2(3h)-furanone (#39), furfural (#47, #48), 2-methylbutanal (#59), and 3-methylbutanal (#60) significantly exceeded those observed at preceding stages. Principle compounds, including dihydro-2(3H)-furanone and furfural, are potentially derived from the associated Maillard reaction during the thermal process [29].  
Figure 2: Fingerprints of SFABT during the entire manufacturing process obtained from GC-IMS: (**A**) two-dimensional topographic plot and (**B**) difference comparison plots.