## 3 Results and Discussion
### Aroma Recombination Verification  
It was well accepted that the predominant odorants obtained by the OAV concept could be confirmed by aroma reconstitution experiments [48]. For this purpose, reconstitution models were prepared containing odorants with high OAVs (OAV \(\geq\) 1) in their actual concentrations in the fresh and dried shitiake mushrooms, respectively. The similarities between the recombination and original samples were judged by the included angle cosine analysis [20]. The results for aroma are summarized in Figure 1, and show that the average similarity degrees were 0.9987 for the fresh samples, and 0.9977 for the dried samples. Thus, it was corroborated that the identification and quantitation of predominant odorants of the fresh and dried shitiake mushrooms could be considered successful, due to the fact that the reconstitution odorants exhibited high similarities to the original samples. Besides, it is shown in (Figure 1) that the mushroom-like odor was reduced after drying. This was due to the decreased OAVs of 3-octanone, 1-octen-3-one and 1-octen-3-ol after drying, which contribute mushroom-like odor. Moreover, the sulfury odor was more intense after drying. This was related to the fact that dimethyl trisulfide and lenthionine had higher OAVs in dried shitake mushrooms. Similarly, the enhancement of sweaty and caramel-like odors after drying might be due to the increased OAVs of isovaleric acid and 4-hydroxy-2,5-dimethyl-3(2H)-furanone, respectively. Variations and Aroma Chemistry of the Key Contributing Odonants in Shitake Mushrooms after Hot-Air-Drying  
Figure 2 shows the key contributing odorants in shitake mushrooms before and after dying and (Figure 3) illustrates the aroma chemistry of the changes. Some key contributing odorants in fresh shitake mushrooms were not detected after drying, including _trans_-4,5-epoxy-(E)-2-decenal (metallic), (E)-2-octenal (fatty, green), octanal (citrus-like), 3-octanone (mushroom) and 3-(methyl-thio)-1-propanol (cooked potato-like). This further illustrated the reasons for the decrease in mushroom-like, metallic, green and fatty characteristics of the aroma after drying (Figure 1A). The loss of odorants might be due to thermal decomposition and oxidation during the drying process, which generated volatile or other compounds [12; 49]. Moreover, there were an additional six key contributing odorants detected in shitake mushrooms after drying, including ethyl acetate (pineapple), 2,3-butanedione (sweet, creamy), dimethyl trisulfide (sulfury), acetic acid (vinegar-like), isovaleric acid (sweaty) and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel). This is the reason for the increase in sulfury, caramel-like and sweaty characteristics of the aroma after drying (Figure 1B). These compounds might be generated from fatty acids by oxidation or degradation, amino acids by Maillard reaction or Strechler and polysaccharides by caramelization or degradation (Figure 3). For example, 4-hydroxy-2,5-dimethyl-3(2H)-furanone could be formed via carbohydrate degradation reactions [50] and 2,3-butanedione and acetic acid were formed via caramelization reactions [21; 51]. There were also eight key contributing odorants detected both before and after drying, including 1-octen-3-ol, lenthionine, 1-octen-3-one, 3-methyl-butanol, 3-(methyl-thio)-1-propanol, phenylacetaldehyde, 3-hydroxy-4,5-dimethyl-2(5H)-furanone and phenylethyll alcohol. However, their concentrations and OAVs also changed after drying as shown in (Figure 4). Among these eight odorants, 1-octen-3-ol (mushroom) showed the most  
Figure 1: Aroma reconstitution models of fresh (**A**) and dried (**B**) shitake mushrooms. significant decrease in concentration, and also in OAV, which was reduced by 357 times. The degradation of 1-octen-3-ol in shiitake mushrooms during drying is displayed in (Figure 5A). Firstly, 1-octene-3-ol generated 1-octene-3-one under the action of alcohol oxidoreductase.