# Effect of Seasoning Addition on Volatile Composition and Sensory Properties of Steved Pork
## 3 Results and Discussion
### PCA and PLS-DA Analysis of Odour-Active Compounds  
In order to clarify the differences in aroma profile of the fresh and stewed pork, a principal component analysis (PCA) was performed and showed in Figure 2a,b. The first principal component (PC1) explained 55.17%, the second principal component (PC2) explained 22.85% and the third principal component (PC3) explained 13.22% of the variations. The first three principal components (PCs) accounted for 91.24% of the total variance and were enough to explain the maximum variation in all original data of the pork samples. As can be seen in Figure 2a, the PC1 and PC2 showed a clear-cut separation of the samples into three major groups. Among them, the sample dot of FP was located in the fourth quadrant, and sample dots representing SP\({}_{3}\), SP\({}_{4}\), SP\({}_{5}\), and SP\({}_{6}\) were located in the second quadrant and could be recognized as one cluster, while sample dots of SP\({}_{1}\) and SP\({}_{2}\) located in the first and fourth quadrant were considered as a group because of their relatively closer distance. As shown in Figure 2b, the fresh and stewed pork samples were divided into four groups in PC1 and PC3, that is, group I: FP; group II: SP\({}_{1}\) and SP\({}_{2}\); group III: SP\({}_{3}\); group IV: SP\({}_{4}\), SP\({}_{5}\), and SP\({}_{6}\). The four group of sample points were located in the different quadrants indicating that the overall aroma of each group of samples were different. Moreover, SP\({}_{4}\), SP\({}_{5}\), and SP\({}_{6}\) samples was close and located in the third quadrant. It can be concluded that the overall flavour of SP\({}_{4}\), SP\({}_{5}\), and SP\({}_{6}\) was similar each other. Similarly, so was SP\({}_{1}\) and SP\({}_{2}\). It can be also found that the flavour of samples SP\({}_{4}\), SP\({}_{5}\) and SP\({}_{6}\) was significantly different from that of sample SP\({}_{3}\) in Figure 2a,b. This showed that the flavour compounds of stewed pork were also affected by soy sauce, sugar, and cooking wine. SP\({}_{6}\), SP\({}_{1}\)-SP\({}_{2}\), FP). It could also be concluded that the overall flavour of SP\({}_{3}\)-SP\({}_{4}\)-SP\({}_{5}\)-SP\({}_{6}\), SP\({}_{1}\)-SP\({}_{2}\) and FP were greatly different, and each group samples possessed the similar flavour profiles. The result is consistent with the PCA analysis (Figure 2a). In addition, to identify the most discriminative volatiles contributing to the observed the fresh and stewed pork samples, variable identification (VID) coefficients were calculated (Figure 3b). Volatiles with VID \(\geq\) 1.0801 discriminating FP, SP\({}_{1}\), SP\({}_{2}\) and SP\({}_{3}\) were predominantly aldehyde compounds (pentanal, (\(Z\))-hept-2-enal, nonanal and (\(E\))-oct-2-enal) and related volatiles (linalool, octane-2,3-dione, ethyl acetate, anethole and estragole). Moreover, no compound with VID \(\geq\) 10.801 was found discriminating SP\({}_{4}\), SP\({}_{5}\), and SP\({}_{6}\). As shown in Figure 3a,b, it can be observed that pentanal, 1-hydroxypron-2-one, D-limonene, ethyl acetate and methanathiol were not only on the opposite side of samples FP, but also strongly and negatively correlated with it (\(-\)0.83 \(\leq\) r \(\leq\)\(-\)0.69), while the remaining 24 odour-active compounds (\(-\)0.57 \(\leq\) r \(\leq\) 0.46) had a low correlation with it. Most odour-active compounds, such as hexanal, heptanal, octanal, (\(Z\))-hept-2-enal, nonanal, (\(E\))-oct-2-enal, decanal, (\(E\))-non-2-enal, (\(E\))-dec-2-enal, (\(E\),\(E\))-2,4-nonnadien, (\(E\),\(E\))-2,4-deceional, oct-1-en-3-ol, (\(E\))-oct-2-en-1-ol, octane-2,3-dione, and 2-pentylfuran, were close to SP\({}_{1}\) and SP\({}_{2}\) on the right side of t1, and the strong and positive correlation (0.60 \(\leq\) r \(\leq\) 0.97) were showed.