## 2 Materials and Methods
### GC-MS Analysis  
An Agilent 7890A GC coupled with an Agilent 7000B mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) was used to analyze the volatile compounds in the Chinese vinegar samples according to a previously described method [28]. An Agilent DB-WAX capillary column (30 m \(\times\) 0.32 mm, 0.25 um film thickness, Agilent Technologies, Santa Clara, CA, USA) was employed to separate the volatile compounds using a carrier gas (helium) at a flow rate of 1 mL/min. The temperature of the oven was programmed as follows: The temperature was increased from 40 \({}^{\circ}\)C to 250 \({}^{\circ}\)C at 5 \({}^{\circ}\)C/min, and maintained at 250 \({}^{\circ}\)C for 3 min. A 5:1 split mode was used under an electron impact mode of 70 eV, with a mass spectrometer interface temperature of 280 \({}^{\circ}\)C, and an ion source temperature of 230 \({}^{\circ}\)C. A selective ion mode was used for the mass scan, ranging from _m/z_ 20 to _m/z_ 450. A 6C-C24 n-alkane series (Supelco, Bellefonte, PA, USA) was used in the same chromatographic conditions to calculate the retention indices. Volatile compounds with available reference standards were identified by comparing their mass spectra and retention indices with the standard, while volatile compounds without available standards were tentatively identified by comparing their mass spectra and retention indices with the Standard NIST11 library and reference literature [29]. The stock solution (5 mL) was mixed with 5 mL distilled water and then consecutively diluted to six concentration level standards, which were extracted and analyzed employing the same procedure used for the Chinese vinegar samples. A quantitative analysis was carried out through the standard curve. In addition, volatile compounds without a standard curve were quantified using standards sharing similar structures or carbon atom numbers.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Code** & **B1** & **B2** & **B3** & **B4** & **B5** & **B6** \\ \hline \multirow{3}{*}{**Product name**} & Ten-year aged & \multirow{3}{*}{\begin{tabular}{c} \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} Ning-hua-mansion \\ old vinegar \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} East-lake \\ health vinegar \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} Qan-he glutinous \\ rice vinegar \\ \end{tabular} } & \multirow{3}{*}{\
\begin{tabular}{c} Heng-shun Jinyou \\ balsamic vinegar \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} Potato vinegar \\ \end{tabular} } \\
**Net content** & & & & & \\
**(mL)** & & & & & \\
**Water, glutinous & & & & & \\ rice, wheat, rice, wheat, & & & & & \\
**Ingredients** & sorghum, corn, & husk, dapu (Barley, & dates, peanuts, & & \\ buckwheat, edible & & & & & \\ salt, sugar & & & & & \\ spices & & & & & \\
**Product** & & & & & & \\
**standard No** & GB/18187 SSF & GB/18187 SSF & GB/19777 SSF & GB/T18187 SSF & GB/T18187 SSF & GB/T18187 SSF \\
**Goods origin** & Meishan, Sichuan & Taiyuan, Shamai & Taiyuan, Shamai & Meishan, Sichuan & Zhenjiang, Jiangsu & Ulanagh, Inner \\
**Product type** & Province & Province & Province & Province & Province & Province & Mongolia \\
**Product type** & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Detailed information on six kinds of Chinese vinegar.