## 4 Discussion  
HS-SPME-GC-MS technology is recognized as a leading method that can be used for extracting and determining aroma substances both domestically and internationally. It utilizes the high temperature of the gas chromatography injection port to analyze the adsorbed components from the stationary phase through chromatography [27]. [PERSON] et al. used this technology to detect the total number of VOC species, 148, at different stages in the maturity of passion fruit, which were mainly esters (approximately 30%), terpen (13%), ketones (11%), aldehydes, alkanes, alcohols, amides, phenols, etc. [28]. In another study, GC-MS analysis identified 48 compounds across three kiwifruit resources, encompassing aldehydes (16), alcohols (11), esters (16), and other compounds (5) [29]. During the course of this study, the technique was fully utilized for the professional identification and precise quantification of 38 plum germplasm resources, resulting in the detection of 138 aromatic components in total, encompassing 26 aldehydes, 63 esters, 13 ketones, 30 alcohols, and six other compounds. The aroma compounds contained in different types of fruits vary somewhat, both in type and in content. Only 30 volatile compounds were detected in Wushancuili plum, encompassing four alcohols, 10 aldehydes, four esters, four acids, three ketones, one alkane, one aromatic compound, two terpen, and one heterocyclic compound. _Prunus salicina_, along with its hybrids, exhibited a considerably greater diversity and higher concentration of volatile compounds compared to _Prunus domestica_ and various other Chinese wild species. While aldehydes were identified as the predominant volatile compounds in both _P. domestica_ and _Prunus spinosa_, it was esters that dominated the volatile profiles in _P. salicina_ and its hybrids, as well as in _Prunus ussuriensis_ fruits [30]. Most researchers believe that the aroma components of plum are mainly aldehydes, esters, alcohols, and ketones, which affect the flavor of the fruit. In this study, we found that 38 varieties of plums contain a large amount of aldehydes, esters, alcohols, and ketones, which are extremely abundant and the main aroma components in plum fruit flesh, with aldehydes and esters accounting for the majority. The positive correlation between the overall quantity of aromatic components and the contents of aldehydes, esters, and ketones  
Figure 4: PCA of 14 extremely key aroma components in 38 plum fruits. was highly significant; this result is similar to [PERSON] et al. 's study on the changes in aroma content during the shelf life of pears with different flesh types [31]. Previous studies have mainly focused on the differences in aroma compounds among different germplasm types, and there have been no reports on the characteristics at different maturity stages. In this study, we found that the cumulative content and quantity of aroma substances in the middle- and late-maturing groups were generally higher than those in the early-maturing group, with a stronger aroma of the middle- and late-maturing plum fruit. By using OPLS-DA, different plum germplasm can be clearly distinguished and clustered into two categories based on maturity. This indicates that the aroma substances of the same maturity germplasm have high similarity but are not entirely the same; the result is similar to the research on lithchi fruits of six special-early-maturing germplasm, as well as early-maturing germplasm [8]. In addition, the VIP value clearly displayed the significantly different aroma substances in various germplasm samples, indicating that these substances can be used as characteristic indicators to distinguish between the 38 plum varieties based on their maturation stages, namely early maturing, and medium and late maturing. A fruit can synthesize hundreds of volatile compounds, but only a small fraction of substances that reach the flavor threshold play a major role in the aroma, which is the characteristic aroma of the fruit [32].