## 3 Results
### Profiles of Volatile Compounds Generated by Different FAs
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**Compounds**} & \multicolumn{4}{c}{**Concentration of Volatile Compounds (\(\upmu\)g/L)**} \\ \cline{3-5}  & & **Blank** & **C16:0** & **C160 + LOX** \\ \hline
1 & Heptanal & 0.00 \(\pm\) 0.00 a & 0.00 \(\pm\) 0.00 a & 1.32 \(\pm\) 0.49 b \\
2 & Nonanal & 0.00 \(\pm\) 0.00 a & 0.00 \(\pm\) 0.00 a & 7.06 \(\pm\) 0.95 b \\
3 & 2-(6-ethoxy-4-methylquinazoline & & 0.00 \(\pm\) 0.00 a & 0.00 \(\pm\) 0.00 a & 1.32 \(\pm\) 0.14 b \\
4 & 2-platinone & 0.00 \(\pm\) 0.00 a & 0.00 \(\pm\) 0.00 a & 12.42 \(\pm\) 1.55 b \\
5 & Cyclopentanone, 3-methyl- & 0.00 \(\pm\) 0.00 a & 0.00 \(\pm\) 0.00 a & 5.02 \(\pm\) 0.27 b \\
6 & Heptane & 0.00 \(\pm\) 0.00 a & 0.00 \(\pm\) 0.00 a & 16.07 \(\pm\) 2.56 b \\
7 & Dodecane & 22.15 \(\pm\) 0.81 c & 0.00 \(\pm\) 0.00 a & 2.56 \(\pm\) 0.26 b \\
8 & Octane & 0.00 \(\pm\) 0.00 a & 28.35 \(\pm\) 0.66 b & 31.38 \(\pm\) 1.41 c \\
9 & Benzene, propyl- & 1.36 \(\pm\) 0.19 b & 0.00 \(\pm\) 0.00 a & 2.71 \(\pm\) 0.92 b \\
10 & Methyl tetradcanoate & 6.71 \(\pm\) 0.20 a & 18.95 \(\pm\) 0.49 c & 16.74 \(\pm\) 1.17 b \\
11 & Pentadecanoic acid, methyl ester & 0.00 \(\pm\) 0.00 a & 22.91 \(\pm\) 2.28 b & 19.79 \(\pm\) 0.72 b \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Changes in the concentrations of volatile compounds produced from C16:0. Figure 3: The number of volatile compounds produced by fatty acid oxidation. 4.2 Changes in the Content of Volatile Compounds Produced from C18:0 and LOX-Induced C18:0 Oxidation  
As indicated in Table 3, the total concentration of volatile compounds in LOX-treated C18:0 reached 289.71 \(\mathrm{\mu g/L}\), which was 0.6 times higher than without LOX, suggesting that LOX promoted the oxidative degradation of C18:0. On the other hand, the total concentration of volatile compounds in the autoxidation system was 172.40 \(\mathrm{\mu g/L}\). C18:0 could be degraded to produce aldehydes, ketones, alkanes, and esters, with heptane being present at the highest concentration (53.78 \(\mathrm{\mu g/L}\)), indicating that strong alkyl radical reactions occurred during autoxidation. The types of aldehydes and ketones increased with LOX treatment. Nonal and 2-nonone were newly detected substances, at concentrations of 7.8 \(\mathrm{\mu g/L}\) and 7.31 \(\mathrm{\mu g/L}\), respectively. LOX promoted C18:0 to produce nonal and 2-nonone. The concentration of heptanaldehyde was 20.73 \(\mathrm{\mu g/L}\) under LOX treatment, which was 0.52 times higher than without LOX treatment (\(p<0.05\)). This suggests that LOX improved the oxidative degradation of C18:0. Moreover, no significant change was observed in the concentration of 2-heptanone with or without LOX treatment (\(p<0.05\)), indicating that 2-heptanone was mainly produced by autoxidation. These degradation products had a positive effect on the overall flavor of mackerel. For instance, heptanal provided a fishy and sweet apricot flavor, while nonal provided an oily and green grass flavor, further demonstrating the importance of C18:0 as a flavor precursor. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**Compounds**} & \multicolumn{4}{c}{**Concentration of Volatile Compounds (\(\mathrm{\mu g/L}\))**} \\ \cline{3-5}  & & **Blank** & **C16:0** & **C160 + LOX** \\ \hline
12 & D-Limonene & 0.00 \(\pm\) 0.00 a & 0.00 \(\pm\) 0.00 a & 0.54 \(\pm\) 0.03 b \\
13 & Butylated Hydroxyltouluene & 1.25 \(\pm\) 0.02 b & 0.00 \(\pm\) 0.00 a & 8.11 \(\pm\) 0.21 c \\
14 & Naphthalene, 1,2,3,4-tetrahydro-1, & 0.00 \(\pm\) 0.00 a & 6.84 \(\pm\) 0.15 b & 10.71 \(\pm\) 1.68 c \\ Total & & 31.47 & 77.05 & 135.75 \\ \hline  & & Values are mean \(\pm\) standard deviation (SD, \(n\) = 3). The letters in the same row indicate that there is a significant difference between the groups (\(p<0.05\)). & & \\ \end{tabular}
\end{table} 
Table 2: _Cont._