## 3 Results
### Analysis of the Volatile Flavor Compounds in the Three Daqu Samples  
The quality and aroma characteristics of _Daqu_, particularly in terms of flavor, are closely tied to their quality in sauce-flavored baijiu. A total of 96 volatile compounds were detected in three samples; BQ contained 55, WQ contained 59, and YQ contained 61. As indicated in Table S1, they were categorized into seven groups based on their chemical structural properties, including esters (19), alcohols (16), acids (16), aldehydes (5), phenols (7), ketones (5), pyrazines (7) and ethers (4), as well as others (17). Similarly to _Daqu_ for manufacturing strong- and light-flavored baijiu [36; 37], esters were also dominant volatile compounds in high-temperature _Daqu_. Moreover, alcohols, acids, pyrazines, and phenols were also the dominant volatile compounds (Figure 2a). Figure 2b illustrates the concentrations of distinct volatile components in several samples. The highest ester content in YQ (71.86 \(\pm\) 12.11 ug/kg) was 4.46 times higher than the lowest content in WQ (16.11 \(\pm\) 2.15 ug/kg), and the ethyl acetate contents in YQ (10.65 \(\pm\) 3.32 ug/kg) and BQ (8.76 \(\pm\) 2.44 ug/kg) were significantly higher than in WQ (1.14 \(\pm\) 0.02 ug/kg). In addition, the content of phenethyl acetate (12.77 \(\pm\) 2.24 ug/kg), hexadecanoic acid ethyl ester (19.78 \(\pm\) 4.53 ug/kg), and n-propyl 9,12-octadecadienoate (13.03 \(\pm\) 0.71 ug/kg) also were the highest in YQ. The alcohol content was significantly higher in YQ (90.66 \(\pm\) 13.73 ug/kg) and BQ (65.25 \(\pm\) 8.23 ug/kg) than in WQ (55.49 \(\pm\) 9.40 ug/kg). Amongst the alcohols, the phenethyl alcohol content in YQ (57.64 \(\pm\) 8.31 ug/kg) was the highest, and the 2,3-butanediol content in WQ (17.13 \(\pm\) 4.18 ug/kg) was the highest. The pyrazines were predominant volatile compounds in the three types of _Daqu_, whose contents were 93.56 \(\pm\) 19.77, 94.12 \(\pm\) 24.41, and 90.15 \(\pm\) 15.89 ug/kg in BQ, WQ, and YQ, respectively. Amongst the pyrazines, tetramethylpyrazine accounted for 31-46% of the total pyrazines, which was the most abundant. The contents of different types of volatile compounds showed significant discrepancies in the different types of _Daqu_. It is worth noting that the volatile compound content in YQ was the highest among the three samples.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sample** & \begin{tabular}{c} **Moisture** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Acidity** \\ **(mmo/10 g)** \\ \end{tabular} & \begin{tabular}{c} **Starch** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Saccharifying** \\ **Power (U)** \\ \end{tabular} & \begin{tabular}{c} **Liquefying** \\ **Power (U)** \\ \end{tabular} & \
\begin{tabular}{c} **Esterifying** \\ **Power (U)** \\ \end{tabular} &
\begin{tabular}{c} **Fermenting** \\ **Power (U)** \\ \end{tabular} \\ \hline BQ & 13.28 \(\pm\) 0.18 \({}^{\text{a}}\) & 1.26 \(\pm\) 0.07 \({}^{\text{a}}\) & 59.26 \(\pm\) 0.33 \({}^{\text{c}}\) & 180.80 \(\pm\) 7.16 \({}^{\text{a}}\) & 0.13 \(\pm\) 0.04 \({}^{\text{b}}\) & 288.36 \(\pm\) 14.61 \({}^{\text{a}}\) & 0.30 \(\pm\) 0.02 \({}^{\text{a}}\) \\ WQ & 10.99 \(\pm\) 0.07 \({}^{\text{c}}\) & 1.264 \(\pm\) 0.05 \({}^{\text{a}}\) & 64.71 \(\pm\) 0.69 \({}^{\text{a}}\) & 113.10 \(\pm\) 2.50 \({}^{\text{c}}\) & 0.18 \(\pm\) 0.01 \({}^{\text{a}}\) & 223.52 \(\pm\) 14.90 \({}^{\text{b}}\) & 0.23 \(\pm\) 0.01 \({}^{\text{a}}\) \\ YQ & 12.19 \(\pm\) 0.16 \({}^{\text{b}}\) & 1.319 \(\pm\) 0.17 \({}^{\text{a}}\) & 62.16 \(\pm\) 0.50 \({}^{\text{b}}\) & 144.40 \(\pm\) 2.71 \({}^{\text{b}}\) & 0.12 \(\pm\) 0.02 \({}^{\text{b}}\) & 198.37 \(\pm\) 17.50 \({}^{\text{c}}\) & 0.27 \(\pm\) 0.01 \({}^{\text{a}}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physicochemical index analysis on three _Daqu_ samples.