## 4 Discussion  
Samples of smoke-flavored sea bass were analyzed at different stages of the production line to determine where the key volatile substances may occur and which processing stage had the greatest impact on the flavor profile of the product. The combination of flavor analysis techniques could be used to better understand the formation of flavor in smoke-flavored sea bass and to control the production chain of smoke-flavored sea bass to improve the flavor quality of the product, which was important for the processing of smoked foods. The diversity of volatile compounds in the different production steps was obtained using a combination of two instrumental analyses, and a total of 85 volatile compounds were initially identified, including 17 aldehydes, 16 phenols, 15 alcohols, 10 ketones, 4 esters, 4 furans, 5 acids, 7 hydrocarbons and 7 other compounds. Three aldehydes (heptanal, benzaldehyde and hexanal) and one furan (2-acetylfuran) had been identified via these two types of analysis methods, while a total of 22 volatile substances may be considered as potential key compounds. From the results, it was found that the two methods differed in their sensitivity to different classes of compounds, with most of the phenolic and heterocyclic compounds being detected by HS-SPME-GC-MS, while HS-GC-IMS detected compounds more inclined to aldehydes, alcohols, and ketones. Some compounds,  
Figure 7: The signal peak volume distribution diagram of volatile compounds of smoke-flavored sea bass with different production steps via HS-GC-IMS. Values with different letters differ significantly (\(p<0.05\)). including 2,4-heptadienal, 2-methyl-1-propanol, 2-methylpropanal, 3-hydroxy-2-butanone, 2-methylbutyric acid, etc., could only be detected by HS-GC-IMS. On the contrary, except for 2-isobutyl-3-methylpyrazine and 2-ethyl-5-methylpyrazine, other heterocycles could only be detected by HS-SPME-GC-MS. Thus, the combination of these two methods provides a more comprehensive aroma characterization [36]. The data [42] show that the volatile compound composition of fresh sea fish is comparable to that of freshwater fish, both of which are composed primarily of aldehydes and carbonyl and alcohol compounds. Most of them have flavor, although sea fish typically have a stronger flavor. HS-SPME-GC-MS results showed high levels of hexanal, nonanal, heptanal, octanal, and 1-octen-3-ol in fresh sea bass samples, with hexanal having an herbaceous taste and generally considered to be a representative substance of fishy taste [43]. Nonanal and octanal might be due to the oxidation of free fatty acids such as linoleic acid [44; 45]. The detected 1-octen-3-ol has a mushroom aroma and influences the overall flavor and known to contribute to the characteristic mild, fresh, plant-like aromas of fresh fish [46]. It was found that the volatiles of the smoked products essentially consisted of the compounds detected in raw fish as well as other compounds produced during processing, as with the results of [PERSON] et al. [47]. The content of these compounds was notably lower in the salted sample (\(p<0.05\)), while other compounds, such as n-octanal and 2-octanol, were not identified, and these phenomena may be related to the oxidation and enzymatic activity of the whole system [48]. However, the HS-GC-IMS results showed an increase in the concentration of aldehydes and alcohols, as with the results of [PERSON] [20]. The specific reasons for the opposite results of the two methods need to be further investigated. The volatile compounds of sea bass after drying were similar to those discovered before salting, despite their different concentrations. Nevertheless, (Z)-7-hexadecenal, trans-2-undecen-1-ol and palmitoleic acid were the new volatile compounds in dried samples. The content of hexanal was higher in fresh, salted, and dried samples, and it was relatively lower in smoked and heated samples, indicating that the components in the smoke flavors had a coordinated and balanced effect on the volatile compounds of fish.