## 2 Results and Discussion
### Aroma-Active Compounds in Doubanjiang  
Studies of the aroma-active compounds of doubanjiang are limited, despite its Chinese Protected Geographical Indication (PGI) status and as traditional fermented food. AEDA was performed for SAFE and HS-SPME. Table 3 shows the aroma-active compounds identified in doubanjiang by SAFE and HS-SPME. A total of 13 aroma-active compounds were detected, including eight by SAFE and eight by HS-SPME. Of these, five aroma-active compounds were verified by both SAFE and HS-SPME. Among them, the seasoning-like compound 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolone) and cooked potato-like compound 3-(methylthio) propanal (methional) were the most intense aroma-active compounds (log\({}_{3}\)FD = 6), followed by 3-isobutyl-2-methoxyyrazine (bell pepper), and \(\beta\)-damascenone (fruit) (log\({}_{3}\)FD = 5), and phenylethyl alcohol (rose) (log\({}_{3}\)FD = 4) identified by SAFE. Ethyl 3-methylbutanoate (ethyl isovalerate) has the highest log\({}_{2}\)FD value (log\({}_{2}\)FD = 4), followed by limonene (fragrant), linalool (bergamot), \(\beta\)-damascenone (fruit), 3-isobutyl-2-methoxyyrazine(bell pepper), and 2-methoxyphenol (bacon) (log\({}_{2}\)FD = 4) identified by HS-SPME. This difference might be due to the extraction method [15]. Compared to SAFE, the selectivity of the fiber also leads to the profiling of different volatile compounds [17]. Sotolone has already been confirmed in previous studies as a key odor-active compound and significantly imparts caramel-like and seasoning-like notes in soy sauce [17; 18; 19]. Sotolone is a furan derivative compound generated by nonenzymatic pathways, which include an aldol condensation step to form the branched six-membered carbon skeleton [20]. Although two furanones, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) and 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF) have been reported as the key aroma compounds in doubanjiang \begin{table}
\begin{tabular}{c c c c} \hline
**Group** & **SF-A** & **XH-B** & **XH-C** \\ \hline aldehydes & 2.87 \(\pm\) 0.41 & 1.16 \(\pm\) 0.28 & 1.56 \(\pm\) 0.26 \\ lactones & 2.35 \(\pm\) 0.27 & 1.21 \(\pm\) 0.12 & 1.28 \(\pm\) 0.15 \\ furans & 1.13 \(\pm\) 0.08 & 0.55 \(\pm\) 0.18 & 0.66 \(\pm\) 0.13 \\ sulfur-containing compounds & 0.71 \(\pm\) 0.02 & 0.58 \(\pm\) 0.16 & 0.87 \(\pm\) 0.08 \\ ethers & 0.71 \(\pm\) 0.04 & 0.26 \(\pm\) 0.03 & 0.11 \(\pm\) 0.02 \\ Miscellaneous compounds & 0.33 \(\pm\) 0.05 & 0.15 \(\pm\) 0.12 & 0.30 \(\pm\) 0.05 \\ \hline \end{tabular}  
* The relative areas of each chemical group compared their total peak areas to that of 3-heptanol (48.585 ug), an internal standard compound, were used as relative quantification analysis. Mean \(\pm\) standard deviation.  
\end{table} 
Table 2: _Cont._ \begin{table}
\begin{tabular}{c c c c c} \hline
**No.** & \multicolumn{2}{c}{**RI**} & **Compounds** & **Log\({}_{3}\)FD a (SAFE)** & **Log\({}_{2}\)SD b (SPME)** \\ \cline{2-5}  & **DB-5 ms** & **DB-wax** & & \\ \hline
3 & 850 & 1075 & ethyl 3-methylbutanoate & 3 & 4 \\
28 & 1029 & 1193 & limonene & - & 3 \\
64 & 1101 & 1551 & linalool & 3 & 3 \\
65 & 1120 & 1933 & phenylethyl alcohol & 4 & - \\
89 & 1391 & 1803 & \(\beta\)-damascenone & 5 & 3 \\
103 & - & 1459 & acetic acid & - & 2 \\
106 & - & 1678 & 3-methylbutanoic acid & 1 & - \\
124 & - & 1510 & 3-isobutyl-2-methoxyyrazine & 5 & 3 \\
126 & 1091 & 1883 & 2-methoxyphenol & - & 3 \\
134 & \(<\)800 & \(<\)1000 & 3-methylbutanal & - & 1 \\
136 & 1050 & 1668 & phenylacetaldehyde & 2 & - \\
152 & 1169 & 2186 & sotolone & 6 & - \\
155 & 911 & 1473 & methional & 6 & 3 \\ \hline \end{tabular}  
* FD: Flavor dilution factor determined on DB-5 ms and DB-wax column. b SD: Sample dilution factor determined on DB-5 ms and DB-wax column.  
\end{table} 
Table 3: Aroma-active compounds detected in doubanjiang by SAFE and HS-SPME-AEDA. (also aka horse bean-chili-paste) [3], sotolone was the most intense aroma-active compound and identified for the first time in doubanjiang.