# Nutrition, Flavor, and Microbial Communities of Two Traditional Bacterial Douchi from Gansu, China
## 3 Results and Analysis
### Analysis of Volatile Flavor Compounds in the Two Types of Douchi
#### 3.2.1 Determination of Volatile Flavor Compounds
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Category**} & \multirow{2}{*}{**Compound Name**} & \multicolumn{2}{c}{**Relative Content (\%)**} \\ \cline{3-4}  & & & **LN Douchi** & **QY Douchi** \\ \hline \hline \multicolumn{4}{c}{**Ketones**} \\ \hline
33 & Acetone & - & 1.99 \(\pm\) 0.53 \\
34 & 2-Butanone & - & 9.27 \(\pm\) 1.14 \\
35 & 2-Pentanone & - & 8.54 \(\pm\) 0.41 \\
36 & 4-Methyl-2-pentanone & - & 0.29 \(\pm\) 0.15 \\
37 & 3-Methyl-2-pentanone & - & 3.01 \(\pm\) 0.35 \\
38 & 2-3-Pentanedione & - & 0.05 \(\pm\) 0.00 \\
39 & 2-Heptenance & - & 0.79 \(\pm\) 0.07 \\
40 & Cyclopentanone & - & 1.41 \(\pm\) 0.29 \\
41 & 2-Octanone & 0.07 \(\pm\) 0.01 & - \\
42 & 5-Methyl-3-heptanone & - & 1.15 \(\pm\) 0.07 \\
43 & 3-Hydroxy-2-butanone & 0.29 \(\pm\) 0.01 b & 0.91 \(\pm\) 0.01 a \\
44 & 3-Octanone & 1.11 \(\pm\) 0.07 & - \\
45 & 2,2,5-Trimethylcyclopentanone & - & 0.13 \(\pm\) 0.01 \\
46 & 2-Hydroxy-3-pentanone & - & 0.15 \(\pm\) 0.03 \\
47 & 2-Nonanone & - & 0.43 \(\pm\) 0.02 \\
48 & 4-Cyclohepten-1-one & - & 2.76 \(\pm\) 0.13 \\
49 & 3,4,4-Trimethylcyclopent-2-enone & - & 0.27 \(\pm\) 0.02 \\
50 & Acetophenone & 0.18 \(\pm\) 0.01 a & 0.25 \(\pm\) 0.01 a \\ \hline \multicolumn{4}{c}{**Aldehydes**} \\ \hline
51 & & Furfural & 0.31 \(\pm\) 0.05 & - \\
52 & & Benzaldehyde & 0.70 \(\pm\) 0.09 & - \\
53 & & 5-Methylfurfural & 0.19 \(\pm\) 0.01 & - \\ \hline \multicolumn{4}{c}{**Terpenoids**} \\ \hline
54 & & Laurylene & 0.83 \(\pm\) 0.09 & - \\
55 & & Limonene & 1.51 \(\pm\) 0.41 & - \\
56 & & \(\gamma\)-Terpinene & 0.07 \(\pm\) 0.03 & - \\
57 & & \(\alpha\)-Pinee & 0.05 \(\pm\) 0.01 & - \\ \hline \multicolumn{4}{c}{**Pyrazines**} \\ \hline
58 & & 2-Methylpyrazine & - & 3.42 \(\pm\) 0.20 \\
59 & & 2,5-Dimethylpyrazine & 2.33 \(\pm\) 0.03 b & 26.77 \(\pm\) 1.26 a \\
60 & & 2,6-Dimethylpyrazine & 1.05 \(\pm\) 0.03 b & 2.32 \(\pm\) 0.01 a \\
61 & & 2,3-Dimethylpyrazine & 1.70 \(\pm\) 0.03 a & 0.49 \(\pm\) 0.03 b \\
62 & & 2-Ethlypyrazine & - & 0.17 \(\pm\) 0.01 \\
63 & & 2-ethyl-5-methylpyrazine & - & 0.15 \(\pm\) 0.01 \\
64 & & 2,3,5-trimethylpyrazine & 6.80 \(\pm\) 0.19 a & 4.71 \(\pm\) 0.25 b \\
65 & & 3-ethyl-2,5-methylpyrazine & - & 0.17 \(\pm\) 0.02 \\
66 & & 2,3,5-trimethyl-6-ethylpyrazine & 0.27 \(\pm\) 0.02 & - \\ \hline \multicolumn{4}{c}{**Furans**} \\ \hline
67 & & 2-Pentyfuran & - & 0.61 \(\pm\) 0.09 \\
68 & & 2-Acetylfuran & - & 0.11 \(\pm\) 0.01 \\ \hline \multicolumn{4}{c}{**Thiazoles**} \\ \hline
69 & & 2,4,5-Trimethylthiazole & 0.96 \(\pm\) 0.01 a & 0.11 \(\pm\) 0.02 b \\ \hline \multicolumn{4}{c}{**Pyridines**} \\ \hline
70 & & 2,3,4,5-Tetrahydropyridine & - & 0.33 \(\pm\) 0.02 \\ \hline \multicolumn{4}{c}{**Pyroles**} \\ \hline
71 & & N-methylpyrrole & - & 1.23 \(\pm\) 0.06 \\ \hline \multicolumn{4}{c}{**Aromatics**} \\ \hline
72 & & Toluene & - & 0.59 \(\pm\) 0.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._A total of 48 volatile compounds were detected in Longnan douchi, and the category with the largest number (15) was esters. The categories with high relative content were esters, pyrazines, and alcohols, and their relative contents were 33.32%, 25.55%, and 14.29%, respectively. The relative content of ligustrazine was the highest in Longnan douchi, and the relative content of 2,4,5-trimethylthiazole, 2,3-dimethylpyrazine, 2,3,5-trimethylpyrazine, ethyl octanoate, 1-octen-3-ol, ligustrazine, and methyl benzoate was significantly higher than that in Qingyang douchi (\(p<0.05\)). Esters were the main category of compounds in Longnan douchi, mainly including ethyl isovalerate, ethyl butyrate, ethyl acetate, etc. They mainly use organic acids and alcohols in douchi as precursors and generate esterification reactions with free fatty acids [20]. In addition, esters can also be extracted from raw materials, such as Baijiu. A total of 41 volatile compounds were detected in Qingyang douchi, the most diverse category was ketones with 16 types.