# HS-SPME Combined with GC-MS/O to Analyze the Flavor of Strong Aroma Baijiu _Daqu_
## 3 Results
### Analysis of Daqu at Different Maturity Stages by HS-SPME Combined with GC-MS  
According to the HS-SPME extraction method in Section 2.4.2, 139 compounds were identified in six different maturity stages _Daqu_ samples (shown in Table 1), including 36 esters, 7 acids and ketones, 22 alcohols, 4 lactones, 8 phenols and furans, 14 aldehydes, 12 nitrogenous compounds, 9 terpenes, 3 sulfur compounds and 9 others. The number of volatile compounds in six different mature stages _Daqu_ was in the order of \"S-3M \(>\) S-22D \(>\) S-10D \(=\) S-0D \(>\) S-6D \(>\) S-4D\". The variation of compounds types in _Daqu_ is shown in Figure 3A, and it can be found that the aroma of _Daqu_ S-3M was more abundant. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**CAS**} & \multirow{2}{*}{**RI**} & \multirow{2}{*}{**Identification \({}^{\textbf{a}}\)**} & \multicolumn{6}{c}{**Area Percentage \% \({}^{\textbf{b}}\)**} \\ \cline{5-10}  & & & & & **S-0D** & & **S-4D** & **S-6D** & **S-10D** & **S-22D** & **S-3M** \\ \hline Esters & & & & & & & & & & \\
1 & Ethyl & 108-64-5 & 1074 & MS,RI & — & 0.525 & 0.765 & — & — & — \\
2 & Isoamyl acetate & 123-92-2 & 1123 & S,MS,RI & — & 1.126 & 0.159 & — & — & 0.082 \\
3 & Ethyl pentanoate & 539-82-2 & 1135 & S,MS,RI & — & — & — & — & 0.335 & — \\
4 & Ethyl hexanoate & 123-66-0 & 1233 & S,MS,RI & 3.760 & 2.489 & 1.230 & 8.698 & 8.656 & 1.122 \\
5 & Ethyl heptanoate & 106-30-9 & 1334 & MS,RI & — & 0.367 & 0.330 & 0.485 & 0.505 & 0.270 \\
6 & Ethyl lactate & 97-64-3 & 1344 & S,MS,RI & — & 0.800 & 0.330 & — & — & 0.530 \\
7 & Hexyl formate & 629-33-4 & 1350 & S,MS,RI & 2.136 & 0.159 & 0.137 & 0.869 & 0.358 & 0.562 \\
8 & 1-Methylheptyl & 2051-50-5 & 1363 & MS & — & — & — & — & 0.038 & — \\
9 & Ethyl octanoate & 106-32-1 & 1435 & S,MS,RI & 1.514 & 1.263 & 1.177 & 0.518 & 0.796 & 0.404 \\
10 & Ethyl nonanoate & 123-29-5 & 1537 & S,MS,RI & — & 0.159 & 0.179 & 0.587 & 0.345 & 0.237 \\
11 & 2-Hydroxy & & 6946-90-3 & 1545 & MS,RI & — & 1.789 & — & — & — \\  & hexanoate & 3-(Methylthio)- & & & & & & & & \\
12 & propane acid ethyl & 13327-56-5 & 1572 & MS,RI & — & 0.665 & 0.268 & 0.111 & 0.132 & 0.137 \\  & ester & & & & & & & & & \\
13 & Hexyl hexanoate & 6378-65-0 & 1611 & S,MS,RI & — & — & — & — & 0.066 \\
14 & Ethyl 2-turoene & 614-99-3 & 1631 & MS,RI & 0.230 & — & — & — & — \\
15 & Ethyl decanoate & 110-38-3 & 1640 & S,MS,RI & — & 1.056 & 1.231 & 0.292 & 0.343 & 0.223 \\
16 & Ethyl benzoate & 93-89-0 & 1674 & S,MS,RI & 0.365 & 0.380 & 0.331 & 0.289 & 0.150 & 0.129 \\
17 & Diethyl succinate & 123-25-1 & 1681 & S,MS,RI & 0.118 & 3.024 & 1.132 & 0.075 & 0.490 & 0.582 \\
18 & Methyl salicate & 119-36-8 & 1786 & S,MS,RI & 0.290 & 0.249 & 0.114 & 0.382 & 0.482 & 0.371 \\
19 & Ethyl phenylacetate & 101-97-3 & 1793 & S,MS,RI & 0.199 & 3.155 & 0.445 & 1.034 & 0.765 & 0.815 \\
20 & Methyl dodecanoate & 111-82-0 & 1803 & S,MS,RI & 0.084 & 0.017 & 0.026 & 0.088 & 0.066 & 0.280 \\
21 & Ethyl & 118-61-6 & 1820 & S,MS,RI & — & — & — & — & 0.069 & 0.198 \\
22 & Phenethyl acetate & 103-45-7 & 1824 & S,MS,RI & — & 0.559 & 0.080 & 0.154 & — & — \\
23 & Ethyl nicotinate & 614-18-6 & 1825 & S,MS,RI & 0.063 & — & 0.110 & 0.136 & 0.119 & — \\
24 & Ethyl dodecanoate & 106-33-2 & 1843 & S,MS,RI & — & 0.689 & 0.889 & 0.562 & 0.596 & 0.480 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Analysis of volatile components in _Duqu_ at different maturity stages. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.