## 4 Discussion
In the smoked sample, the contents of 2,3-pentanedione and 2-butanone decreased significantly (\(p<0.05\)), which may be affected by microbial activity [49; 50]. However, the smoked samples contained phenolics not found in fresh sea bass, such as guaiscal (2-ethylphenol) and eugenol. These phenolics are derived from the smoky flavor and have been identified as the most characteristic smoke-related components in smoked fish [51]. Notably, new volatile compounds were identified in the smoked samples because of further interactions of the components in the smoke flavors with proteins, peptides and free amino acids, which are characteristic compounds of the smoked flavor [52]. Benzaldehyde was present at low levels in unsmoked fish, but it was elevated after smoking, indicating that benzaldehyde was present in both unsmoked fish and the smoke flavors, similarly to the findings of [PERSON] et al. [53]. Ketones are the products of the oxidation of unsaturated fatty acids and the Maillard reaction [54]. Hydroxyl acetone, 2,3-dimethylcyclopent-2-en-1-one, and 3-methyl-2-cyclopent-1-one were more likely to be derived from the smoke flavors, where 3-methyl-2-cyclopentene-1-one has a typical scorched taste [55]. [PERSON] et al. [56] found that the ketones from 2-cyclopent-1-one were most likely derived from the Maillard reaction of cellulose pyrolysis during fumigation. At the same time, hexanal, 2-butanone and 2,3-pentanedione disappeared after \"Smoke flavoring\", which may be due to the bad smell covered by the smoke flavors, or some chemical reactions occurred between the organic components in the \"smoke flavoring\". In addition, higher levels of undecane, dodecane, tridecane and heptadecane were detected in smoked fish flesh than in unsmoked fish flesh, which may be related to the lipid precursors in unsmoked fish [57; 58]. The content of aldehydes (benzaldehyde), ketones (3-hydroxy-2-butanone) and alcohols (1-propanol) increased significantly with the processing of smoke-flavored sea bass, which was probably due to irreversible chemical reactions such as Strecker degradation or lipid oxidation. The precursors of butanal in fish flesh are mainly oleic (MUFA n-9) and linoleic acid (PUFA n-6) or its methyl esters [59]. Five saturated linear aldehydes, hexanal, heptanal, octanal, nonanal and valeraldehyde, had been identified as characteristic volatile compounds [60]. Although aliphatic aldehydes such as hexanal and glutaraldehyde have been found in wood smoke, most of them come from the oxidation of lipids in fish during the smoking process [58] and interact with proteins [61]. It has been found that heat treatment at higher temperatures can facilitate the production of aldehydes, which can degrade polyunsaturated fatty acids (linoleic acid, linolenic acid) more quickly, resulting in the production of hexanal, heptanal and other aldehydes. Simultaneously, fatty acids oxidation leads to an increase in the content of alcohols [62], whose odor threshold is usually higher than that of aldehydes, and their special flavor (floral, fruity) would promote the formation of fish aroma. The detected 1-pentanol had a significant effect on flavor [63]. When fish was processed, saturated ketones with specific flavor (fruity, cheesy) and diketones with caramel or other flavors may be associated with the degradation of amino acids and oxidation of polyunsaturated fatty acids [64]. The results showed that the contents of volatile compounds in smoke-flavored sea bass were significantly increased in dried and heated samples, which were more due to the significant increase of ketones (Figure 5). Ketones mainly came from the oxidation of polyunsaturated fatty acids or the degradation or oxidation of amino acids [64]. Saturated ketones had a unique fragrance, cheesy and fruity flavor, whereas diketones had a sweet, buttery, and caramel flavor [65].