## 3 Results and Discussion
### The Volatile Profile of Shihtake mushrooms under Different Hot Air Drying Conditions by CG-MS  
In general, GC-IMS analysis was a more sensitive detection of trace substances and obtained fingerprint information, but the focus of GC-IMS analysis was not to identify a single volatile compound [35]. Hence, the volatile compounds were comprehensively analyzed by GC-MS in this study. A total of 28 volatile compounds were identified by GC-MS combined with HS-SPME in the three shihtake mushroom samples, shown in Table 2. Eight compounds were detected by both GC-MS and GC-IMS, including 1-octen-3-ol, 3-octanone, benzaldehyde, dimethyl trisulfide, hexanal, acetic acid, phenylacetaldehyde, and 3-methylbutanal. The difference in the identified volatile components by GC-MS and GC-IMS might be due to the different working conditions and focal points of the two detection methods [36]. GC-MS was performed under phase heating and vacuum conditions and focused on qualitative and quantitative accuracy of substances, while GC-IMS was performed under constant temperature and atmospheric pressure and more focused on distinguishing samples [18; 36]. This also stated the necessity of the combination of GC-IMS and GC-MS for the flavor analysis. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**RI**} & \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**CAS Number**} & \multirow{2}{*}{**ID**} & \multicolumn{3}{c}{**Concentrations (\#g/g)**} \\ \cline{5-6}  & & & & & **Sample A** & **Sample B** & **Sample C** \\ \hline \multicolumn{6}{c}{Sulfur compounds (7)} \\ \hline
1 & 735 & Carbon disulfide & 75-15-0 & RI, MS & 6.17 \(\pm\) 1.34 b & 9.34 \(\pm\) 0.29 a & 7.18 \(\pm\) 0.34 b \\
4 & 1083 & Dimethyl disulfide & 624-92-0 & RLMS,S & 0.71 \(\pm\) 0.02 c & 1.07 \(\pm\) 0.10 b & 1.42 \(\pm\) 0.09 a \\
9 & 1252 & Thiovanic acid & 68-11-1 & RLMS & ND & ND & 0.20 \(\pm\) 0.03 a \\
12 & 1350 & Dimethyl trisulfide & 3658-80-8 & RLMS,S & 2.06 \(\pm\) 0.34 c & 3.37 \(\pm\) 0.72 b & 5.37 \(\pm\) 0.29 a \\
20 & 1709 & 1,2,4-Trithiolane & 289-16-7 & RLMS & 12.77 \(\pm\) 0.15 c & 20.35 \(\pm\) 2.56 a & 15.84 \(\pm\) 0.63 b \\
27 & 2196 & 1,2,4,5-Tetrathiane & 291-22-5 & RLMS & 2.09 \(\pm\) 0.33 b & 3.31 \(\pm\) 0.8 a & 2.70 \(\pm\) 0.11 ab \\
28 & 2498 & 1,2,4,6-Tetrathtiepane & 292-45-5 & RLMS & 0.83 \(\pm\) 0.12 a & 0.74 \(\pm\) 0.00 a & 0.92 \(\pm\) 0.10 a \\ Total content of sulfur compounds & & & & 24.63 \(\pm\) 2.00 b & 38.18 \(\pm\) 3.78 a & 33.63 \(\pm\) 0.89 a \\ \hline \multicolumn{6}{c}{C8 compounds (3)} \\
10 & 1260 & 3-Octanone & 106-68-3 & RLMS,S & 0.10 \(\pm\) 0.03 b & 3.55 \(\pm\) 0.33 a & 0.05 \(\pm\) 0.01 b \\
15 & 1446 & 1-Octen-3-ol & 3391-86-4 & RLMS,S & 1.59 \(\pm\) 0.27 b & 4.38 \(\pm\) 0.33 a & 0.34 \(\pm\) 0.04 c \\
22 & 1900 & Phenylethyl alcohol & 60-12-8 & RLMS,S & 2.83 \(\pm\) 0.49 a & 3.47 \(\pm\) 0.35 a & 3.46 \(\pm\) 0.22 a \\ Total content of C8 compounds & & & & 4.52 \(\pm\) 0.75 b & 11.40 \(\pm\) 0.34 a & 3.84 \(\pm\) 0.21 b \\ \hline \multicolumn{6}{c}{Miscellaneous (18)} \\
2 & 934 & 3-Methylbutanal & 590-86-3 & RLMS,S & 1.86 \(\pm\) 0.03 ab & 1.59 \(\pm\) 0.10 b & 2.16 \(\pm\) 0.36 a \\
3 & 1056 & (E)-2-Butenal & 123-73-9 & RLMS & ND & 1.82 \(\pm\) 0.40 a & ND \\
5 & 1103 & Hexanal & 66-25-1 & RLMS & 0.17 \(\pm\) 0.06 b & 0.30 \(\pm\) 0.01 a & 0.20 \(\pm\) 0.01 b \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Identification of volatile compounds of shihtake mushrooms with different hot-air-drying conditions. Among the 28 volatile compounds identified by GC-MS, 23 compounds, 24 compounds, and 20 compounds were identified, and the total contents of the identified volatile compounds were 41.02 ug/g, 70.18 ug/g and 53.83 ug/g, in sample A, B and C, respectively. The sample B not only had more varieties of volatile compounds, but also showed significant higher abundance in volatile compounds than sample A and C (_p_ < 0.05). This stated that lower dryness degree would enrich the volatile flavor.