## 3 Results
### Volatile Compounds Detection Using GC-MS
#### 3.1.3 Aldehydes  
Aldehyde formation may be enhanced by oxidation after a long aging period [39]. Seven aldehydes were present in all the samples, including 3-methylbutyraldehyde, nonanal, ben  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**No.** & **B1** & **B2** & **B3** & **B4** & **B5** & **B6** \\ \hline
1 & 26.130 & 125.103 & 156.666 & 114.390 & 60.834 & 93.584 \\
2 & 118.177 & 170.431 & 173.433 & 22.156 & 22.386 & 227.178 \\
4 & 11.220 & 1.914 & — & 9.659 & 4.218 & 7.165 \\
7 & 14.479 & 123.443 & 69.205 & 12.564 & 13.876 & 263.524 \\
8 & 41.605 & 12.813 & — & 46.109 & 73.764 & 2.244 \\
9 & — & — & — & — & 5.698 & — \\
14 & — & 1.905 & — & 2.080 & — & — \\
15 & 4154.525 & 3420.799 & 4034.055 & 5790.261 & 3526.653 & 3075.922 \\
19 & 3645.795 & 3208.173 & 5195.313 & 2781.376 & 5331.364 & 2762.692 \\
20 & — & 4.165 & 1.221 & — & — & 25.182 \\
21 & — & — & — & — & 3.679 & — \\
22 & — & — & — & — & 1.133 & — \\
23 & 191.887 & 119.274 & 97.302 & 136.356 & 233.104 & 72.358 \\
24 & 3.993 & 7.174 & 5.834 & 2.927 & 9.514 & 1.403 \\
27 & — & — & — & — & — & 1.067 & — \\
28 & 613.975 & 194.026 & 102.920 & 753.580 & 927.503 & 231.874 \\
29 & — & 49.359 & — & 17.635 & 2.641 & 66.542 \\
30 & 21.738 & 86.984 & 16.267 & 19.342 & 18.783 & 1.986 \\
32 & 65.961 & 2017.506 & 241.127 & 28.278 & 38.555 & 60.044 \\
37 & — & 2.433 & 1.723 & — & — & — \\
39 & 15.642 & 245.762 & 20.371 & 7.726 & — & — \\
43 & 7.372 & 19.470 & 4.672 & 8.375 & 9.111 & 6.361 \\
46 & 16.181 & 63.629 & 52.470 & 29.662 & 3.817 & — \\ \hline \end{tabular} The number of compounds corresponds with Table 2. The code of vinegar corresponds with Table 1.  
\end{table}
Table 5: Odor activity values (OAVs) of vinegar compounds.  
zaldehyde, phenylethanal, 1H-pyrrole-2-carbaldehyde, 5-methyl-2-phenyl-2-hexenal, and 1-methylpyrrole-2-carboxaldehyde. Of these, benzaldehyde may be derived from the oxidation of benzyl alcohol or the action of microorganisms on phenylalanine, phenol, phenylacetic acid, and hydroxybenzoic acid [40]. Phenylethanal is formed via the Strecke degradation of phenylalanine during the acetic acid fermentation stage [41]. Here, 3-methylbutyratealdehyde was most abundant in B1, B2, B3, B4, and B5 at levels of 39,262.87 ug/L, 22,572.34 ug/L, 19,246.37 ug/L, 35,396.43 ug/L, and 44,409.15 ug/L, while phenylethanal was the highest in B6 at 12,303.69 ug/L. The 1-methylpyrrole-2-carboxaldehyde levels were lowest in all the samples at 36.40 ug/L, 135.69 ug/L, 489.55 ug/L, 27.11 ug/L, 92.43 ug/L, and 14.36 ug/L in B1, B2, B3, B4, B5, and B6, respectively.  
The aldehyde compounds displayed significant diversity and were highly abundant in the vinegar, providing fruity, floral, fatty, waxy, and fragrant aromas [9]. These components substantially affected the overall aroma characteristics of the different types of vinegar. Phenylethanal contributed sweet, roasted, green, nutty, and floral notes, significantly affecting the aroma profiles of B1 (OAV = 4154.525), B2 (OAV = 3420.799), B3 (OAV = 4034.055), B4 (OAV = 5790.261), B5 (OAV = 3526.653), and B6 (OAV = 3075.922). The benzaldehyde concentration contributed fruity, nutty, woody, and floral notes while reaching odor thresholds in B2 (OAV = 1.905) and B4 (OAV = 2.080).