## Results and Discussion
### Volatile Profile of Different Peach Cultivars Using GC-MS
#### 3.1.1 The Construction of VOCs Profiling for Eight Peach Cultivars
Among these, butyl acetate, (Z)-3-hexen-1-yl acetate and hexyl acetate was detected in all samples and the levels were significantly different between samples. (E)-2-hexen-1-yl acetate was also detected at high levels in most cultivars. The remaining unmentioned esters were present at less than 10 \(\mu\)g/kg in each sample, so these components were not the focus of this study. A total of 11 terpenids were identified, of which linalool, \(\beta\)-myrrene and D-limonene were detected in all peach cultivars with significant differences. [PERSON] et al. [24] identified linalool as one of the key aroma compounds of peach fruit that increased significantly with fruit ripening and has floral aroma properties [25; 26]. The order of linalool content in all samples was as follows: JC > HH > JXIANG > HJML > XFML> DTML > JG > JXIU. Surprisingly, the linalool content in JC was more than twice that of HH. Previous studies have shown that nectarines contain higher levels of linalool than peaches [7]. Although the material in this study did not include nectarines, JC was derived from peach Jinxiu and nectarine Huyou 018, which may be the reason for its highest linalool content among the eight cultivars. \(\beta\)-myrrene is reported as a precursor of linalool and is one of the common terpenids in peaches and nectarines [27; 28]. Here, the content of \(\beta\)-myrcene ranked consistently with linalool in the eight cultivars. More than 10 lactones have been found in peaches [6; 27; 29]. Here, we identified six lactones: \(\gamma\)-hexalactone, \(\gamma\)-decalactone, \(\gamma\)-octadecanotone, \(\gamma\)-heptalactone and \(\delta\)-decalactone. Consistent with previous studies [7], \(\gamma\)-decalactone, \(\delta\)-decalactone and \(\gamma\)-hexalactone were the leading lactones with the highest content in these elite cultivars, with the difference that \(\delta\)-decalactone was the most abundant in the present study. As reported, mid- and later-ripening cultivars have higher lactone content than early-ripening cultivars [30]. However, in this study, some early- and mid-maturing cultivars such as HJML and JC had the highest total lactone content, while the late-maturing cultivar JXIU had the lowest content (Figure 2), which might be related to its genetic background and cultivation conditions. Five ketones were detected, and \(\beta\)-ionone and 2-octanone were detected in all samples. The content of total ketone was highest in 'XFML' and lowest in 'JX' (Figure 2). Interestingly, dihydro-\(\beta\)-ionone was detected in all white flesh peaches, but not in all yellow flesh peaches; this result is similar to that of several researchers [31]. This is due to the fact that C-13-norisoprenoids such as dihydro-\(\beta\)-ionone in peach fruit are mainly synthesized via the isopenoid pathway, and carotenoids are precursors for their synthesis. Carotenoids in white-flesh peaches are cleaved to disubstituted carotenoids via the action of carotenoid cleavage dioxygenase (CCD4), which in turn forms the volatile compounds such as dihydro-\(\beta\)-ionone, while the CCD4 enzyme gene in yellow-flesh peaches is mutated and cannot degrade carotenoids, so less dihydro-\(\beta\)-ionone is synthesized than in white-fleshed peaches [32; 33]. To further understand the differences of volatiles in different peach cultivars, a cluster analysis heat map was constructed (Figure 3). The vertical axis of the figure represents different volatiles and the horizontal axis represents different peach cultivars. The red-to-blue and large-to-small circles indicate the abundance of volatiles from highest to lowest. According to the content of each of the VOCs, cluster analysis clustered JXIU, DTML, JG and XFML into one group. This indicates that the composition and content of their volatiles are similar. Horizontally, the numerous volatiles were roughly divided into three clusters. Cluster 1 covers most of the aldehydes and alcohols. In general, this cluster of compounds is relatively higher in XFML and JG.