## 3 Results and Discussion
### The Volatile Fingerprints of Shitiake Mushrooms under Different HAD Processing by HS-GC-IMS
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**RI**} & \multirow{2}{*}{**Compound**} & \multicolumn{2}{c}{**CAS**} & \multirow{2}{*}{**Formula**} & \multirow{2}{*}{**Comment**} \\  & & & **Number** & & \\ \hline
1 & 990.8 & 1-Octen-3-ol & 3391-86-4 & C8H16O & \\
2 & 991.0 & 3-Octanone & 106-68-3 & C8H16O & Monomer \\
3 & 991.8 & 3-Octanone & 106-68-3 & C8H16O & Dimer \\
4 & 975.3 & Benzaldehyde & 100-52-7 & C7H6O & Monomer \\
5 & 975.3 & Benzaldehyde & 100-52-7 & C7H6O & Dimer \\
6 & 973.2 & Dimethyl trisulfide & 3658-80-8 & C2H683 & \\
7 & 794.6 & Hexanal & 66-25-1 & C6H12O & Monomer \\
8 & 795.4 & Hexanal & 66-25-1 & C6H12O & Dimer \\
9 & 742.3 & (E)-2-Pentenal & 1576-87-0 & C5 HBO & \\
10 & 739.5 & 3-Methyl-1-butanol & 123-51-3 & C5H12O & Monomer \\
11 & 740.2 & 3-Methyl-1-butanol & 123-51-3 & C5H12O & Dimer \\
12 & 709.7 & Propyl acetate & 109-60-4 & C5H10O2 & Monomer \\
13 & 707.4 & Propyl acetate & 109-60-4 & C5H10O2 & Dimer \\
14 & 603.6 & Ethyl acetate & 141-78-6 & C4H8O2 & Monomer \\
15 & 604.1 & Ethyl acetate & 141-78-6 & C4H8O2 & Dimer \\
16 & 559.5 & 2-Methylpropanal & 78-84-2 & C4H8O & \\
17 & 583.5 & Acetic acid & 64-19-7 & C2H4O2 & \\
18 & 507.6 & 2-Propanol & 67-63-0 & C3H8O & \\
19 & 502.6 & Acetone & 67-64-1 & C3H6O & \\
20 & 476.2 & Ethanol & 64-17-5 & C2H6O & Monomer \\
21 & 480.4 & Ethanol & 64-17-5 & C2H6O & Dimer \\
22 & 724.2 & Acetoin & 513-86-0 & C4H8O2 & \\
23 & 624.9 & 2-Methyl-1-propanol & 78-83-1 & C4H10O & Monomer \\
24 & 625.2 & 2-Methyl-1-propanol & 78-83-1 & C4H10O & Dimer \\
25 & 1102.4 & 1-Nonanal & 124-19-6 & C9H18O & \\
26 & 1067.5 & (E)-2-Octenal & 2548-87-0 & C8H14O & \\
27 & 1065.2 & Phenylacetaldehyde & 122-78-1 & C8H8O & \\
28 & 903.5 & Heptanal & 1111-7-7 & C7H14O & \\
29 & 862.0 & (E)-2-Hexenal & 6728-26-3 & C6H10O & \\
30 & 588.7 & Butanal & 123-72-8 & C4H8O & \\
31 & 662.4 & 2-Methylbutanal & 96-17-3 & C5H10O & \\
32 & 645.8 & 3-Methylbutanal & 590-86-3 & C5H10O & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Identification of volatile flavor compounds in shitake mushrooms with different hot-air-drying conditions by GC-IMS. zaldehyde, (E)-2-octenal, (E)-2-pentenal, 3-octanone, phenylacetaldehyde, butanal, showed obviously higher concentrations in sample B than those in sample A and C, whereas these 29 components showed similar levels between sample A and C. Moreover, the concentrations of 12 components (in the green rectangle) in sample B, including 2-methylbutanal, 3-methylbutanal, ethyl acetate, acetic acid, ethanol, 2-propanol, were markedly lower than those in sample A and C, and sample A were close to sample C with respect to these seven components. Additionally, four components (in the yellow rectangle) in sample A exhibited the highest concentrations and four components (in the black dashed rectangle) in sample C displayed the most abundant in contents among the three samples. Overall, the gallery plot demonstrated that sample B was obviously different from sample A and C, while sample A and C were similar compared with sample B. It might be due to the fact that the different drying extent between sample B and sample A and C led to different reactions and a differential reaction process. [PERSON] et al. [16] has reported that volatile compounds in shihtake mushrooms changed significantly when drying progress approached to the constant weight. The volatile fingerprints obtained by GC-IMS revealed that samples with different drying degree were different and drying degree exerted more influence on the volatile flavor quality than the drying rate.