## 2 Results and Discussion  
### Aroma-Active Compounds in Yongchuan Douchi  
To eliminate the influence of solvent, solid-phase microextraction (SPME) was used before SAFE (solvent assisted flavor evaporation) distillation. The SAFE distillate displayed the typical aroma of Yongchuan douchi. The volatiles were extracted by both SPME and SAFE and characterized through GC-O and GC-MS. A total of 49 aroma-active compounds were detected (Table 1). The aroma compounds were identified and characterized by comparing their RIs, mass spectra and odor descriptions with NIST library and reference standards, which included 11 acids, 7 aldehydes, 7 ketones, 7 pyrazines, 6 heterocyclic compounds, 5 phenols, 3 alcohols, 2 sulfur-containing compounds and 1 ester. There were two compounds with RI values of 2135 (herbal note) and 2380 (burnt note) that were temporarily unidentified. The various sensory properties of different kinds of aroma components indicated the complex flavor of douchi and that contribute to the unique flavor to Yongchuan douchi. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**No.** & **Compounds** & **Odor * & \multicolumn{2}{c}{**RI *b**} & \multicolumn{2}{c}{**Identification Methods *c**} & \multicolumn{2}{c}{**Extraction Method 4**} \\ \hline
1 & 2-methyl/lutantal & mality & 918 & MS/RI/O/STD & & SPME \\
2 & 2,3-butanedione & butter & 969 & \textless{}700 & MS/RI/O/STD & SAFE & \\
3 & 1-hydroxy-2-pyenoenoene & herbal & 1306 & MS/RI/O/STD & SAFE & \\
4 & 2-5-dimethylpyrazole & multy & 1333 & 973 & MS/RI/O/STD & SAFE & SPME \\
5 & 6-methyl-5-hepper2-one & grassy & 1344 & MS/RI/O/STD & SAFE & SPME \\
6 & 2-isopropyl-5-methyl-2-hexen & herbal & 1367 & 1167 & MS/RI/O/STD & SAFE & SPME \\
7 & dimethyl trisulfide & garlic & 1386 & 1025 & MS/RI/O/STD & SAFE & SPME \\
8 & 2-ethyl-6-methylpyrazole & roasted potato & 1394 & 1060 & MS/RI/O/STD & SAFE & SPME \\
9 & 2,3-5-trimethypytrazine & nutty skin & 1416 & 1065 & MS/RI/O/STD & SAFE & SPME \\
10 & acetic acid & pungnent sour & 1419 & \textless{}700 & MS/RI/O/STD & SAFE & SPME \\
11 & 2-ethyl-3-3-dimethylpyrazole & multy & 1452 & 1141 & MS/RI/O/STD & SAFE & SPME \\
12 & 3-(methylthio)propionaldehyde & roasted potato & 1462 & 912 & MS/RI/O/STD & SAFE & SPME \\
13 & tetramethylpyrazole & chocolate & 1476 & MS/RI/O/STD & SAFE & \\
14 & 2-ethyl-6-methylpyrazole & multy & 1495 & MS/RI/O/STD & SAFE & \\
15 & decanal & green, soap-like & 1502 & 1264 & MS/RI/O/STD & SAFE & \\
16 & formic acid & vineger & 1512 & MS/RI/O/STD & SAFE & \\
17 & benzaldehyde & almond & 1527 & 1017 & MS/RI/O/STD & SAFE & SPME \\
18 & 2-3-butanedol & fruity & 1542 & 889 & MS/RI/O/STD & SAFE & \\
19 & 3-methylbutonic acid & rancid & 1570 & MS/RI/O/STD & SAFE & \\
20 & acetylpyrazole & popcorn & 1631 & MS/RI/O/STD & SAFE & SPME \\
21 & buylev acid & rancid & 1639 & MS/RI/O/STD & SAFE & SPME \\
22 & benzeneacetaldehyde & flora & 1649 & 1100 & MS/RI/O/STD & SAFE & SPME \\
23 & 3-methylbutonic acid & rancid, fruity & 1674 & 958 & MS/RI/O/STD & SAFE & \\
24 & \textless{}7-caprolactone & fruity & 102 & MS/RI/O/STD & SAFE & SPME \\
25 & 5-methyl-2-furanmethanol & caramel & 1723 & MS/RI/O/STD & SAFE & SPME \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Aroma compounds detected in Yongchuan doucli.