## 2 Materials and Methods
### GC-MS/O Analysis  
The GC-MS/O analysis was performed following the modified method described by [PERSON] et al. [14]: 50 mL of the baijiu samples were diluted with Milli-Q water to reach an ethanol concentration of 15%, and 1.5g NaCl was added, then extracted 3 times with CH\({}_{2}\)Cl\({}_{2}\) (50 mL each time). The combined extract (approximately 150 mL) was extracted three times with Na\({}_{2}\)CO\({}_{3}\) (50 mL each time, 0.25 mol/L, pH 10.0), and then washed with 50 mL saturated NaCl solution. The neutral/alkaline fraction obtained was marked NBF. The combined aqueous phase (approximately 200 mL) was adjusted to pH 2.0 with HCI (4.0 mol/L) and extracted three times with CH\({}_{2}\)Cl\({}_{2}\) (70 mL each time) to obtain the acidic fraction named AF. After being dried with anhydrous Na\({}_{2}\)SO\({}_{4}\), the two fractions were concentrated to 500 \(\mu\)L by using a Wechsler fractionation column and stored at \(-20\)\({}^{\circ}\)C before GC-O analysis.  
Three trained panelists were selected to conduct the GC-O analysis. During the GC operation, the panelists positioned their noses close to the sniffing port and responded to the intensity of the eluted aroma, recording the aroma descriptors (Odor), intensity values, and corresponding retention times. Intensity was assessed using a six-point scale ranging from 0 to 5: 0 represented \"none,\" 1 represented \"very weak,\" 2 represented \"weak,\" 3 represented \"medium,\" 4 represented \"strong,\" and 5 represented \"very strong.\" The Osme value for aroma intensity was calculated as the average of the ratings provided by the three panelists.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**No.** & **Brand** & **Label** & **Region** &
\begin{tabular}{c} **Alcohol Content** \\ **(\% vol)** \\ \end{tabular} & **Manufacturer** & **Location** \\ \hline
1 & Wuliangchun & WLC & Sichuan & 52\% & Sichuan Yibin Wuliangye & \\
2 & Wuliangye & WLY & Sichuan & 52\% & Group Co., Ltd. & Yibin, China \\
3 & Gujinggong & GJ & Jianghuai & 52\% & Anhui Gujing Gongjiu & Bozhou, \\  & & & & Co., Ltd. & China \\
4 & Tianzhilan & TZL & Jianghuai & 52\% & Jiangsu Yanghe Distillery & Suqian, China \\ \hline \end{tabular}
\end{table}
Table 1: Information about the baijiu samples.  
The GC-O instrument was a Trace1300-ISQ7000 (Thermo, Waltham, MA, USA) equipped with a ODP3 sniffing port (Gerstel, Linthicum Heights, MD, USA). A DB-WAX column (30 mm \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m) was used. The injector temperature was set at 250 \({}^{\circ}\)C, and the injection was performed in splitless mode. Helium (purity \(\geq\) 99.999%) was used as the carrier gas in constant linear velocity mode with a flow rate of 1.0 mL\(\cdot\)min\({}^{-1}\). The temperature program was as follows: the initial temperature was set at 40 \({}^{\circ}\)C, increased to 50 \({}^{\circ}\)C at a rate of 10 \({}^{\circ}\)C\(\cdot\)min\({}^{-1}\), held for 10 min, then increased to 80 \({}^{\circ}\)C at a rate of 3 \({}^{\circ}\)C\(\cdot\)min\({}^{-1}\), held for 10 min, and finally increased to 250 \({}^{\circ}\)C at a rate of 5 \({}^{\circ}\)C\(\cdot\)min\({}^{-1}\) and held for 5 min. The temperature at the sniffing port was maintained at 250 \({}^{\circ}\)C. The EI voltage was set at 70 eV. The ion source temperature was 280 \({}^{\circ}\)C, the transfer line temperature was 250 \({}^{\circ}\)C. Mass spectra were acquired over a mass range of 35-350 amu. Solvent delay was 3.5 min.  
Compounds were identified by comparing the odor, retention indices (RI), mass spectrum, and standard compounds (Std). Volatile compounds were initially identified by searching the NIST 20 library, and Std were subsequently analyzed under the same conditions. Final identification was achieved by comparing the RI and mass spectra of volatile compounds in the samples with those of the Std. RI were calculated based on the retention times of C6-C40 n-alkanes obtained under the same GC-MS analysis conditions.