# HS-SPME Combined with GC-MS/O to Analyze the Flavor of Strong Aroma Baijiu _Daqu_
## 3 Results
### Analysis of Active Aroma Compounds in Daqu S-3M by GC-MS/O  
According to the qualitative results in Table 1, the volatile components of _Daqu_ at different maturity stages are quite different. The greater variety and content of aromas in the _Daqu_ S-3M determined the final use of it in actual production. The following _Daqu_ S-3M was taken as the object to explore the active aroma compounds. GC-MS/O analyzed the active aroma compounds in _Daqu_ S-3M. A total of 50 aroma regions were smelled under different polarity chromatographic columns, except for seven compounds that were not successfully identified. Forty-three compounds were identified by mass spectrometry, retention index, and standard substance as shown in Table 2: including 8 esters, 2 lactones, 7 alcohols, 8 aldehydes, 5 nitrogenous compounds, 4 phenols and acids, 3 terpen, 1 sulfur compound, and another compound (naphthalene). In Table 2, No. 6 (2,6-dimethylpyrazine), No. 8 (dimethyl trisulfide), No. 14 (acetic acid), No. 16 (2-ethyl-3,5-dimethylpyrazine), No. 19 (benzaldehyde) No. 22 (\(\beta\)-caryophyllene), No. 24 (butanoic acid), No. 29 (3-methylbutanoic acid), No. 41 (guaiacol), No. 43 (phenethyl alcohol), No. 45 (4-ethyl-2-methoxyphenyl), No. 46 (\(\gamma\)-nonanolactone), and No. 49 (methyl palmitate) had higher olfactory intensity. In addition, many compounds with low olfactory intensity might affect the overall aroma profile of _Daqu_[26] because they can have high flavor thresholds. Esters are the main flavor substances in baijiu, and most of the short-chain esters with the flavor of fruit odor, including No. 2 (ethyl butyrate), No. 3 (ethyl valerate), and No. 5 (ethyl hexanoate). Long-chain fatty acid esters, such as methyl palmitate, have a high threshold but show a significant wax flavor, which may be related to the characteristic aroma of _Daqu_[23]. There are many types of esters, and their olfactory intensities are relatively low except for No. 49 (methyl palmitate). In addition, among the three lactones identified in S-3M, _Daqu_, \(\gamma\)-nonanolactone, and \(\gamma\)-butyrolactone showed aroma activity, and \(\gamma\)-nonanolactone with coconut flavor also had high aroma intensity. The results showed that lactones played a significant role in the aroma of baijiu, while \(\gamma\)-nonanolactone was one of the essential aroma compounds. A large number of alcohols were identified in this experiment, but the olfactory intensity was low. The smell intensity of phenethyl alcohol and benzyl alcohol containing a benzene ring was relatively high, showing flower, sweet, and honey fragrance. In addition to No. 44 (2-phenyl-2-butenal, sweet aroma), _Daqu_ also had more aldehydes after storage, which mainly showed a typical compound aroma of grass and oil, bitter almond, and so on. It can be seen from Table 2 that the relative content of No. 44 (2-phenyl-2-butenal) among the seven aldehydes identified in _Daqu_ was S-0D (0.037%) \(<\) S-3M (0.457%). In addition, the relative content of nonanal, (\(E\))-2-ocenal, phenylacetaldehyde, (\(E\))-2-nonenal, phenylacetaldehyde, and 2,4-decaelian is S-0D \(>\) S-3M. The compound aroma of these aldehydes has an essential influence on the flavor of _Daqu_. Phenol compounds have high odor intensity, which were important aroma active compounds in _Daqu_. Guaiacol, 4-ethyl-2-methoxyphenyl, and 2-methoxy-4-vinylphenol were characterized with wood flavor, clove, scorch bitter taste, etc., while \(p\)-cresol has an animal odor. Pyrazine compounds (nitrogenous compounds) are considered the primary source of coke flavor and baking flavor in _Daqu_[23]. In addition, 2,5-dimethylpyrazine and 2,6-dimethylpyrazine are considered essential aroma compounds in medium and high temperature _Daqu_. The five pyrazines identified in this experiment are wheat flavor, roasted flavor, and potato flavor. Dimethyl trisulfide (garlic) and naphthalene (grass) also had higher olfactory intensity in _Daqu_. Dimethyl trisulfide was considered a vital aroma substance in SAB [6].