# Effects of Drying Process on the Volatile and Non-Volatile Flavor Compounds of _Lentinual edodes_
## 3 Results and Discussion
### HS-SPME-GC-MS Analysis of Volatile Compounds of L. edodes
It was reported that ketones are mainly obtained from the Maillard reaction and the oxidation and degradation of unsaturated fatty acids [27], and ketones can also be produced by degradation of esters [28]. However, in this study, the most probable route may be through enzymatic reactions. The preservation or formation of ketones in _L. eodes_ was not conducive when the FD temperature was not appropriate [14]. The flavor differences between fresh and dried _L. eodes_ were obvious. The \"mushroom flavor\" of fresh _L. eodes_ is described as a sweet, earthy and cheesey aroma, while the shitake flavor of dried _L. eodes_ is similar to that of onion and garlic [29]. Eight-carbon compounds are ubiquitous among mushrooms, which are a key contributor to mushroom flavor [9; 30]. As shown in Table 1, the contents of eight-carbon compounds in fresh, FD, HAD, and ND mushrooms were 1271.85 \(\mu\)g/g, 131.18 \(\mu\)g/g, 38.89 \(\mu\)g/g and 242.69 \(\mu\)g/g, respectively. The contents of 1-octen-3-ol in in fresh, FD, HAD, and ND mushrooms were 857.02 \(\mu\)g/g, 103.78 \(\mu\)g/g, 5.72 \(\mu\)g/g and 105.30 \(\mu\)g/g, respectively. The contents of 1-octen-3-one and 3-octanone in in fresh, FD, HAD, and ND mushrooms were 244.08 \(\mu\)g/g, 17.13 \(\mu\)g/g, 27.96 \(\mu\)g/g and 118.24 \(\mu\)g/g, respectively. Generally, 1-octen-3-ol, 1-octen-3-one and 3-octanone were the major C8 compounds in mushrooms. 1-octen-3-ol, also called mushroom alcohol, feature with a typical odor of mushrooms [29]. 1-octen-3-one and 3-octanone could produce a similar odor like 1-octen-3-ol [31]. As shown in Table 1, 1-octen-3-ol and 1-octen-3-one were detected in all of the four mushrooms, and fresh mushrooms had the highest level of 1-octen-3-ol and 1-octen-3-one. 3-octanone was detected in fresh, FD, and HAD mushrooms, and FD mushrooms had the highest amount. However, other research \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Compounds**} & \multirow{2}{*}{**RI \({}^{\text{a}}\)**} & \multicolumn{5}{c}{**Contents (\(\mu\)g/g)**} & \multirow{2}{*}{**ID \({}^{\text{e}}\)**} \\  & & \(\mathbf{F}\)\({}^{\text{b}}\) & & & & \\ \hline
1,3-Xylene & 865 & nd & 0.05 & 0.04 & 0.03 & A \\ P-Isopropyltoluene & 1021 & 1.06 & 0.32 & nd & 0.03 & A \\ D-Limonene & 1025 & 17.43 & 10.54 & 7.74 & 0.78 & A \\ Naphthalene & 1176 & 0.30 & 0.33 & 0.54 & 0.02 & A \\ Dodecane & 1199 & 0.16 & 0.38 & nd & nd & A \\
5-Ethyl2-methyl-octane & 1280 & 0.95 & nd & nd & nd & A \\
3-Carene & 1283 & nd & 0.07 & nd & nd & B \\ Decane & 1288 & nd & 0.13 & nd & nd & A \\
**Hydrocarbons** & b-Elemen & 1390 & nd & 0.08 & nd & A \\
**(17)** & Tetradecane & 1400 & 0.56 & 0.14 & 0.09 & 0.00 & A \\ Germacrene D & 1477 & nd & 0.08 & nd & nd & A \\ (-)-a-Selinenea- & 1491 & nd & 0.20 & nd & nd & A \\ Pentadecane & 1501 & 0.91 & 0.39 & nd & nd & A \\ Hexadecane & 1600 & nd & 0.11 & 0.05 & 0.02 & A \\ Heptadecane & 1697 & nd & 0.05 & nd & nd & A \\ Eicosane & 2000 & 0.14 & 0.06 & nd & nd & A \\
**Total hydrocarbons** & & 21.51 & 12.93 & 8.46 & 0.88 & \\ \hline \hline \end{tabular} RI \({}^{\text{a}}\), retention index. F \({}^{\text{b}}\), fresh shitake mushroom; FD, freeze drying sample; HAD, hot-air drying sample; ND, natural drying sample. eight-carbon \({}^{\text{c}}\) compounds. nd \({}^{\text{d}}\), not detected. Identification e: A, a comparison of mass spectrum and RI with authentic standards; B, comparison of mass spectrum and RI with published data and Wiley 7.0 and NIST05 MS library.  
\end{table} 
Table 1: _Cont._reported that 1-octen-3-ol and 3-octanone were the dominant compounds in the dried _L. edodes_ (vacuum, microwave, microwave vacuum, convective drying, vacuum-microwave drying and freeze-drying) [12; 1]. The differences were possibly due to the different volatile compound extraction methods. In sum, drying processes changed the contents of C8 compounds, which resulted in weaker \"mushroom flavor\" for dried _L. edodes_ compared with fresh _L. edodes_.