## 3 Results and Discussion
### Aroma Properties of Shitiake Mushrooms under Different Hot Air Drying Conditions by DSA
#### 3.4.1 Comparison Analysis of Shitiake Mushrooms Based on Volatile Fingerprints by PCA and FSA
The sample A and sample C had a small distance along the PC1 and were both on the left side, whereas sample B was on the right side and away from sample A and C. This demonstrated that the sample B was different from sample A and C, with respect to aroma profile consisting of volatile compounds and aroma properties. As shown in Figure 5, sulfury attribute was near to the sample C and the sample B, and far from the sample A. It illustrated that the sample C and sample B had the remarkable sulfur odor, and on the contrary the sample A had the weak sulfur odor. Additionally, the other 6 aroma attributes, including cooked potato, mushroom, seasoning, chocolate, caramel and sweat, were close to the sample B. It illustrated that the sample B was the most prominent in these aroma properties among the three samples. Furthermore, among the six aroma attributes, cooked potato, mushroom, and seasoning were nearer to the sample C than the sample A, no matter along the PC1 or PC2. This stated that these odors were more intense in the sample C than those in the sample A. It is noticeable that these results  
Figure 5: The partial least squares regression (PLSR) analysis between volatile compounds and aroma properties of shitiake mushrooms. obtained by PLSR were consistent with those by DSA, further elucidating that the PLSR analysis was rational and effective in this study. Moreover, it was shown in Figure 5 that 3-octanone, (E)-2-butenal, 2-methyl-2-butenal, 2-phenylpropenal, 2-phenyl-2-butenal, hexanal, 1-pentanol, carbon disulfide, 1,2,4-trithiolane, 1,2,4,5-tetrathtihiane, 1-octen-3-ol, phenol, and \(\beta\)-methyl-benzeneethanol, were closely linked to the sample B. As shown in Table 2, these compounds were only detected in the sample B or had significant higher concentrations than those in sample A and sample C. This gave the reason to their close relationship with the sample B. It has been reported that ketones, alcohols and aldehydes have been reported as the main volatile compounds in fresh shitake mushrooms [10; 45]. But drying dehydration could result in the loss of ketones, alcohols and aldehydes [46]. Ketones, alcohols and aldehydes were easily destroyed through a series of enzymatic and non-enzymatic reactions during drying [15]. Thus, sample B with lower drying degree retained more ketone, alcohol and aldehyde compounds. 3-Methylbutanal, acetic acid, isovaleric acid, thiovanic acid, and 1,2,4,6-tetrathtiepane were relatively close to the sample C, illustrating that they were the representative compounds of the sample C. It was consistent with the results of GC-MS analysis that the sample C had outstanding abundance in these compounds. Additionally, the sample A was associated with phenylethane and 2-ethylcapric acid as shown in Figure 5, which were only detected in the sample A by GC-MS. In addition, the relationship between aroma properties and volatile compounds also could be illustrated in Figure 5. Sulfury attribute was highly correlated with dimethyl disulfide and dimethyl trisulfide. These two compounds have been reported to be the key odorants in dried shitake mushrooms [47]. Cooked potato attribute was positively associated with \(\beta\)-methyl-benzeneethanol and 1,2,4,5-tetrathtiane. Mushroom-like odor was strongly associated with 1,2,4-trithiolane and carbon disulfide. Hexanal was regarded as the main contributor to seasoning attribute. 1-Pentanol had a good correlation with chocolate attribute. Caramel attribute was closely related to 3-octanone, 2-methyl-2-butenal, (E)-2-butenal, 2-phenylpropenal and 2-phenyl-2-butenal. These volatile flavor substances which were strongly associated with aroma attributes might impact the overall aroma of shitiake mushrooms markedly.