# HS-SPME Combined with GC-MS/O to Analyze the Flavor of Strong Aroma Baijiu _Daqu_
## 3 Results
### Quantitative Analysis of Aroma Components in Daqu by MHS-SPME

Table 2: Analysis of active aroma compounds in Daqu after storage (S-3M). compound was lower than 11.75%. The experimental repeatability was good at the same time. The recoveries of the compounds ranged from 83.58% to 120.05%, which met the needs of experimental quantification. In the quantitative analysis, the content range was 12.93 ng/g-2816.28 ng/g. The content of furfuryl alcohol (2816.28 ng/g) with the burned taste was the highest. In addition, the content of phenylacetaldehyde, guaiacol, nonanal, and \(\gamma\)-butryrolactone was higher than 500 ng/g. The contents of 2-phenyl-2-butenal, 2-ethyl-3,5-dimethylpyrazine, geranyl acetone, and 3-ethyl-2-methylpyrazine were lower than 100 ng/g. The content of the compound only indicates the amount of the compound in the sample, which can not reflect the effect of the compound on the overall flavor of the sample. For example, furfuryl alcohol had the highest content, but its olfactory intensity was low. Therefore, based on quantitative analysis, combined with the threshold value of compounds, OAV value was calculated to evaluate the effect of different compounds on the overall flavor of samples [26]. The OAV values of 21 compounds were calculated as shown in Table 3, and 18 compounds OAVs \(\geq\) 1, which contributed greatly to the overall aroma of _Daqu_ and were important flavor compounds in _Daqu_ aroma. In exploring Baijiu flavor, grain aroma is often described as one of the flavor descriptors and is an important flavor branch of baijiu flavor quality evaluation. Nine compounds related to \"grain aroma\" have higher OAV values except for geranyl acetone (OAV = 1). (_E,E_)-2,4-decadienal has the highest OAV value (OAV = 2746) among them. (_E,E_)-2,4-decadienal (OAV = 2746), nonanal (OAV = 655), phenylacetaldehyde (OAV = 447), (_E_)-2-nonenal (OAV = 339), hexanal (OAV = 81), 4-ethyl-2-methoxyphenol (OAV = 40), (_E_)-2-octenal (OAV = 40), and \(\gamma\)-nonanolactone (OAV = 10) have an important contribution to _Daqu_ aroma. It was consistent with other literature that nonanal and 4-ethyl-2-methoxyphenol were considered aroma active substances in _Daqu_[26]. In addition, eight compounds had OAV \(\geq\) 1. Among them, guaiacol (OAV = 172), 2-methoxy-4-vinylphenol (OAV = 122), 2-ethyl-3,5-dimethylpyrazine (OAV = 43), furfuryl \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Compounds** & **Threshold */(ppb)** & **OAVs** \\ \hline
6 & 2,6-Dimethylpyrazine & 200 & 2 \\
7 & 2,3-Dimethylpyrazine & 10823.7 & \textless{}1 \\
9 & 3-Ethly-2-methylpyrazine & 130 & \textless{}1 \\
10 & Nonanal & 1 & 655 \\
11 & 2,3,5-Trimethylpyrazine & 10 & 24 \\
13 & (E)-2-Octenal & 3 & 40 \\
16 & 2-Ethyl-3,5-dimethylpyrazine & 1 & 43 \\
19 & Benzaldehyde & 30 & 5 \\
20 & (_E_)-2-Nonenal & 0.6 & 339 \\
22 & \(\beta\)-Caryophyllene & 64 & 2 \\
25 & \(\gamma\)-Butryolactone & 50 & 11 \\
26 & Phenyacetaldehyde & 4 & 447 \\
27 & Furfuryl alcohol & 100 & 28 \\
34 & 2,4-Decadienal & 0.07 & 2746 \\
37 & Geranyl acetone & 60 & 1 \\
41 & Guaiacol & 5.5 & 172 \\
44 & 2-Phenyl-2-butenal & - & - \\
45 & 4-Ethly-2-methoxyphenol & 6.9 & 40 \\
46 & \(\gamma\)- Nonanolactone & 21 & 10 \\
48 & 2-Methoxy-4-vinylphenol & 3 & 122 \\
50 & Hexanal & 25.48 & 81 \\ \hline \hline \end{tabular}  
*: Check the threshold of the corresponding compound on [[http://www.leffingwell.com](http://www.leffingwell.com)]([http://www.leffingwell.com](http://www.leffingwell.com)) (accessed on 23 July 2020).  
\end{table} 
Table 3: OAV calculation for the quantitative compounds. alcohol (OAV = 28), 2,3,5-trimethylpyrazine (OAV = 24), 2-ethyl-3,5-dimethyllyprazine (OAV = 22), and \(\gamma\)-butyrolactone (OAV = 11) were higher.