## 2 Results and Discussion
### Aroma-Active Compounds in Yongchuan Douchi
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{**No.**} & \multicolumn{1}{c}{**Compounds**} & \multicolumn{1}{c}{**Odor 1 **} & \multicolumn{1}{c}{**Identification Methods 4 **} & \multicolumn{1}{c}{**Extraction Method 5 **} \\ \hline
26 & citronello & flora & 1766 & 1288 & MS/RI/O/STD & SAFE & SPME \\
27 & 3-methylvaleric acid & sweaty & 1800 & 954 & MS/RI/O/STD & SAFE & SPME \\
28 & 4-methylvaleric acid & sweaty & 1808 & 1038 & MS/RI/O/STD & SAFE & SPME \\
29 & 6-d-transacome & flora, honey & 1819 & MS/RI/O/STD & SAFE & SPME \\
30 & methyl+cyclopentemolone & herbal & 1828 & MS/RI/O/STD & SAFE & SPME \\
31 & 3-methyl-1,2-cyclopentemadiene & ceremellated & 1899 & 1090 & MS/RI/O/STD & SAFE & SPME \\
32 & 2-methyl-polyopentanol (guiarol) & woody, smoly & 1861 & 1151 & MS/RI/O/STD & SAFE & SPME \\
33 & phenethyl alcohol & rogy & 1910 & MS/RI/O/STD & SAFE & SPME \\
34 & 3-hydroxy-2-methyl-4H-PYA-4-core (maltol) & malty & 1964 & 1181 & MS/RI/O/STD & SAFE & SPME \\
35 & 2-acetylpyrrole & bread & 1971 & 1124 & MS/RI/O/STD & SAFE & SPME \\
36 & phenel & plastic & 2008 & MS/RI/O/STD & SAFE & \\
37 & 2-pentadecome & green & 2019 & MS/RI/O/STD & SAFE & \\
38 & \(v\)-nonolactone & coconut-like & 2031 & 1424 & MS/RI/O/STD & SAFE & SPME \\
39 & octanoic acid & rancid & 2067 & MS/RI/O/STD & SAFE & \\
40 & 5-methyl+2-phenyl-2-hexen & mntry, cocoa & 2076 & MS/RI/O/STD & SAFE & \\
41 & \(p\)-rccel & burnt & 2085 & MS/RI/O/STD & SAFE & \\
42 & unknowl * & herbal & 2135 & & & \\
43 & Eugenol & woody, spicy & 2168 & 1420 & MS/RI/O/STD & SAFE & \\
44 & methyl palmitate & wax & 2215 & 1916 & MS/RI/O/STD & SAFE & SPME \\
45 & 2-dihydro-3,5-dihydroxy-6-methyl-4(H-PYA-4-core & burnt & 2223 & 1212 & MS/RI/O/STD & SAFE & \\
46 & 2-6-dimethoyophenol & smoly & 2265 & 1413 & MS/RI/O/STD & SAFE & \\
47 & levulinic acid & vinegar & 2343 & 1138 & MS/RI/O/STD & SAFE & \\
48 & unknowz 2 ** & \multicolumn{1}{c}{**The compounds can be handled by sniffing**} \\
49 & benzoic acid & balsam & 2458 & 1243 & MS/RI/O/STD & SAFE & \\
50 & phenylacetic acid & flora & 2573 & 1230 & MS/RI/O/STD & SAFE & \\
51 & dihydro-4-hydroxy-2-(H)-furanone & wax & 2606 & MS/RI/O/STD & SAFE & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._To figure out the importance of these odorants in the overall aroma profile, odor-active compounds in the douchi distillate were further investigated by applied aroma extract dilution analysis (AEDA) using GC-O. The analysis revealed 22 odorants (Table 2) with high FD factors (between 8 and 2048) which were recognized as aroma-active compounds of Yongchuan douchi. Four acids were obtained for acetic acid (pungent sour, FD = 2048), 3-methylbutanoic acid (rancid, FD = 512), 4-methylvaleric acid (sweaty, FD = 16) and 3-methylvaleric acid (sweaty, FD = 8). These organic acids provided a sour, rancid aroma to the douchi's flavor and have been detected in Yangjiang douchi; among them, 3-methylbutanoic acid was identified as an active-aroma compound reported in Yangjiang douchi [23]. The odorants with relatively high FD factors of 2,3-butanedione (FD = 512) and \(\gamma\)-nonanolactone (FD = 512) were also recognized as significant components of douchi flavor. The \(\gamma\)-nonanolactone produced a milky note in the douchi flavor, and 2,3-butanedione was described as a fatty butter aroma, both of which have been discovered as aroma-active compounds in several fermented soybean foods [17; 20]. Two sulfur-containing compounds with high FD values were another important class of aroma-active compounds found in Yongchuan douchi. The 3-(methylthio)propionaldehyde (FD = 256) is generally considered to have the aroma of roasted potato and the function of enhancing soya sauce-like flavor, which is one of the most common key aroma substances found in fermented soybean food products [14; 16]. Dimethyl trisulfide (FD = 32) provided a typical sulfuretted and onion-like aroma, and it was detected in doubanjiang [24] (a kind of fermented soybean paste).