## 3 Results
### Quantitation of Aroma-Active Compounds  
Given the extremely low contents or low contributions and combined with the reports of literature, finally, 70 aroma compounds (26 esters, 12 alcohols, 10 acids, seven aldehydes, two ketones, five phenols, three terpenes, and five others) were quantified by constructing calibration curves of each one. The quantitative methodological parameters are given in Table S4. The concentrations of aroma compounds varied in four different grades of FJ (Table 2). The contents of most aroma compounds in high-grade FJ were higher than those in low-grade FJ. [PERSON] et al. [13] found that the content of esters, alcohols, and acids increased with the increase in the quality grades of Caoyuanwang (CYW, a kind of LFB), and [PERSON] et al. [16] also suggested that the premium-grade sesame-flavor Baijiu had the highest aroma concentrations. The findings declared that high-grade Baijiu might have higher aroma concentrations. These may be due to the different aging years and blending proportions of their base liquors. The results of the Duncan test showed that ethyl octanoate, 3-methylbutyl hexanoate, ethyl decanoate, ethyl benzoate, ethyl dodecanoate, ethyl 3-phenylpropanoate, 2-heptanol, 1-octen-3-ol and 4-methylguaiacol had significant differences among four samples, which were likely to play a key role in differentiating the differences between different grades of FJ. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Aroma Compound**} & \multicolumn{4}{c}{**Concentration (\#g/L)**} \\ \cline{3-5}  & & **F00** & **F10** & **F20** & **F30** \\ \hline Esters & & & & \\
4 & Ethyl acetate \({}^{*}\) & 1282.25 \(\pm\) 35.69 \({}^{\text{a}}\) & 1006.35 \(\pm\) 25.97 \({}^{\text{c}}\) & 1205.99 \(\pm\) 17.75 \({}^{\text{b}}\) & 1209.86 \(\pm\) 33.36 \({}^{\text{b}}\) \\
5 & Ethyl propanoate & 5824.68 \(\pm\) 489.78 \({}^{\text{a}}\) & 6142.42 \(\pm\) 892.68 \({}^{\text{a}}\) & 4922.67 \(\pm\) 318.86 \({}^{\text{a}}\) & 4137.84 \(\pm\) 135.58 \({}^{\text{b}}\) \\
6 & Ethyl 2-methylpropanoate & 966.65 \(\pm\) 34.52 \({}^{\text{c}}\) & 1252.69 \(\pm\) 51.26 \({}^{\text{b}}\) & 1243.91 \(\pm\) 34.23 \({}^{\text{b}}\) & 1595.64 \(\pm\) 75.59 \({}^{\text{a}}\) \\
7 & 2-Methylpropyl acetate & 733.23 \(\pm\) 66.56 \({}^{\text{b}}\) & 784.76 \(\pm\) 49.95 \({}^{\text{ab}}\) & 837.95 \(\pm\) 41.63 \({}^{\text{ab}}\) & 892.57 \(\pm\) 54.36 \({}^{\text{a}}\) \\
9 & Ethyl butanoate & 1943.70 \(\pm\) 215.88 \({}^{\text{b}}\) & 2069.28 \(\pm\) 190.70 \({}^{\text{b}}\) & 2385.55 \(\pm\) 132.67 \({}^{\text{b}}\) & 2795.18 \({}^{\text{b}}\) \\
11 & Ethyl 2-methylbutanonate & 102.60 \(\pm\) 102.0 \({}^{\text{b}}\) & 1244.04 \(\pm\) 7.72 \({}^{\text{b}}\) & 132.31 \(\pm\) 4.04 \({}^{\text{b}}\) & 198.22 \(\pm\) 147.2 \({}^{\text{a}}\) \\
13 & Ethyl 3-methylbutanoate & 107.64 \(\pm\) 11.05 \({}^{\text{c}}\) & 127.67 \(\pm\) 7.81 \({}^{\text{b}}\) & 138.02 \(\pm\) 5.39 \({}^{\text{b}}\) & 230.55 \(\pm\) 18.85 \({}^{\text{a}}\) \\
17 & 3-Methylbutyl acetate & 3040.63 \(\pm\) 419.90 \({}^{\text{b}}\) & 3298.69 \(\pm\) 349.05 \({}^{\text{ab}}\) & 4008.56 \(\pm\) 249.74 \({}^{\text{a}}\) & 4102.69 \(\pm\) 327.75 \({}^{\text{a}}\) \\
18 & Ethyl pentanoate & 293.59 \(\pm\) 5.56 \({}^{\text{c}}\) & 2870.5 \(\pm\) 11.53 \({}^{\text{c}}\) & 513.16 \(\pm\) 32.43 \({}^{\text{a}}\) & 348.26 \(\pm\) 144.69 \({}^{\text{b}}\) \\
22 & Ethyl hexanoate & 4105.70 \(\pm\) 52.29 \({}^{\text{a}}\) & 4754.95 \(\pm\) 72.99 \({}^{\text{b}}\) & 5193.83 \(\pm\) 258.16 \({}^{\text{a}}\) & 5526.09 \(\pm\) 93.14 \({}^{\text{a}}\) \\
24 & Hexyl acetate & 31.54 \(\pm\) 0.60 \({}^{\text{b}}\) & 33.05 \(\pm\) 0.15 \({}^{\text{ab}}\) & 37.43 \(\pm\) 3.86 \({}^{\text{a}}\) & 33.50 \(\pm\) 0.61 \({}^{\text{ab}}\) \\
25 & 3-Methylbutyl butanoate & 6.80 \(\pm\) 0.11 \({}^{\text{ab}}\) & 7.59 \(\pm\) 0.91 \({}^{\text{a}}\) & 7.44 \(\pm\) 0.97 \({}^{\text{ab}}\) & 5.81 \(\pm\) 0.36 \({}^{\text{b}}\) \\ \hline \hline \end{tabular}
\end{table}