## 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 PCA evaluated the regularity and difference among samples and the contribution of principal components by determining principal component factors instead of complex variables in the original samples [25; 41]. Figure 4a demonstrated the score plot of PCA analysis. The first and second principal components (PC1 and PC2) represented 81% and 17%, respectively, and added up to 98% of the total variables. This indicated that the PCA could represent most information of the samples. The PCA obtained by the dynamic PCA module has also been successfully applied in the discrimination analysis in studies of kiwifruits [21], oil [42], shrimp [43], and pufferfish [44], based on the volatile fingerprints obtained by GC-IMS. As shown in Figure 4a, the sample A and C were at the right side. They were hardly separated along the PC1, but could be separated a little along the PC2. Sample B were at the left side and could be separated evidently from sample A and C, especially along the PC1. This illustrated that sample A and C were similar, compared with sample B. As shown by loading plots, ethyl acetate and dimethyl trisulfide was in close relationship with sample C. This may be due to the fact that drying contributed to the formation of dimethyl trisulfide [15; 16]. Additionally, 3-methyl-1-butanol was close to sample A and hexanal was connected with sample B. This was illustrated by the fact  
Figure 3: Radar chart of shitiake mushrooms with different hot-air-drying conditions by descriptive sensory analysis (DSA). that 3-methyl-1-butanol and hexanal stood out in sample A and B, respectively. These were consisted with information shown in the gallery plot. In addition, the Figure 4b showed that the three samples could be clearly divided into three categories, indicating their dissimilarities. But among the three samples, close distances between sample A and C and long distances between sample B and sample A and C were observed. It demonstrated that sample A and C were similar and sample B was more different. The results observed by the FSA were consistent with the PCA. The two advanced chemometric methods both demonstrated the more similarities of the samples that were processed at different drying rate and the same drying degree, and more dissimilarities of the samples that were processed at the same drying rate and different drying degree. And this further revealed that flavor characteristics were influenced more by drying degree than by drying rate. Figure 4: Principal component analysis (PCA) linked loading plots (**a**) and fingerprint similarity analysis (FSA) (**b**) of shitake mushrooms under different hot air-drying conditions. 4.2 Comparison Analysis of Shitiake Mushrooms Based on Volatile Compounds and Aroma Properties by PLSR  
PLSR was utilized to show the characteristic of samples and relationship among the samples, volatile compounds and sensory properties based on the results of GC-MS and DSA. It has been successfully applied in volatile characteristic and comparison analysis of the shitiake mushrooms processed by three drying technologies [14] and three kinds of kiwifruits [21], also based on the volatile compounds obtained by GC-MS and sensory properties by DSA. In the PLSR analysis, X variable was designed as aroma properties and Y variable was designed as volatile compounds (RMSE 0.7396, R\({}^{2}\) 0.9931). As shown in Figure 5, the PLSR provided a two-factor model, in which the inner, middle, and outer ellipses represented 50%, 70% and 100% of the interpreted variance, respectively. Most of the volatile compounds and sensory properties were placed between the inner and outer ellipses, suggesting that the model could be used to accurately account for these variables [21]. It could be seen from Figure 5 that the PC1 was the most important components and accounted for 83%.