## 3 Results and Discussion
### Principal Component Analysis (PCA) of the Characteristic Aroma of coconut Jams  
Although the quantitative and qualitative analysis could measure the aroma compounds present in the coconut jams at different concentration times, these methods were not able to determine the characteristic aroma components in the samples. PCA is a multivariate statistical analysis method that employs multiple variables to linearly transform the data to select fewer important variables [(43)]. Thus, this method can be used to determine the characteristic aroma components of the overall aroma of the dominant coconut jam. The first principal component (PC1) and the second principal component (PC2) explain changes in the data variance of 59.35% and 17.84%, respectively. The cumulative contribution rates of PC1 and PC2 reached a high level, which was sufficient to explain the maximum variation of the aroma substances in the coconut jams during the concentration process.  
As shown in the scatterplot of PC1 and PC2 in Figure 6a, seven coconut jam samples were clearly distributed in the three spatial regions of the PCA plot. The after-sterilization samples were located in the region covering the positive axis of PC1 and the positive axis of PC2. The associated aroma components could be ethylidene acetone (4), pentanal-2-methyl (6), dihydro-2-methyl-3(2H)-furanone (9), furfuryl alcohol (12), methional (15), 2-butanoylfuran (16), 2-5-dimethylpyrazine (17), formic acid, heptyl ester (18), benzencarbonal (19), hexanoic acid (20), 2-pentylfuran (21), 3,6-dimethyl-tetrahydroproyran-2-one (23), delta-nonalactone (30) and delta-dodeclactone (32) (Figure 6b); these 14 compounds may be the characteristic aroma components of the post-sterilization samples.  
The 0 min and 4 min samples were located in the top left corner of the region covering the negative axis of PC1 and the positive axis of PC2. The aroma associated with the 0 min and 4 min samples could be 3-hydroxy-2-butanone (2), decanoic acid (26), dodecanal (28), ethyl octanoate (33), isopentyl alcohol (3), pentyl alcohol (7), hexyl formate (11), ethyl caproate (22) and 2-methyl-1-butanol (5), implying that these compounds may be the main aroma components of the 0 min and 4 min samples (Figure 6b).  
The 8 min, 12 min, 16 min and 20 min samples were mainly located in the bottom left corner of the region covering the negative axis of PC1 and the negative axis of PC2 (20 min was situated along the positive axis of PC1), implying that the aroma was steady from 8 min to 20 min. The aroma associated with these times could be propyl acetate (1), 2-octanone (13), 2-octanol (14), 2-nonanone (25), (3E)-6-methyl-3-undecene (24), ethyl decanoate (27) and 5-hexyl-4-methyldihydro-2(3H)-furanone (29), (Figure 6b), suggesting that these compounds could be the characteristic aroma components at these times. It is worth noting that at this stage it can be divided into two subgroups of 8-12 min and 16-20 min. Among them, the related compounds 2-octanol (14), ethyl decanoate (27), 2-octanone (13) and (3E)-6-methyl-3-undecene (24) decreased significantly from 12-16 min, which may be the continuous rise in temperature leading to the compounds undergoing the process of first synthesis and degradation. Eventually, the flavor of coconut jam changes at this stage.  
According to PCA analysis results, the change in the aroma of coconut jam during the concentration process can be divided into three stages: the initial stage, the middle heating stage, and the sterilization stage (Figure 6a). The aroma of coconut jam after high temperature sterilization significantly differed from the aroma of the first two stages, and new flavor compounds such as furans and pyrazines were formed. Therefore, after sterilization, the coconut jam had a relatively obvious caramel aroma. Overall, the results of the PCA show that the odor of coconut jam at each stage was formed by the combined action of multiple individual aroma compounds.