## Results
### Construction of Aroma Fingerprinting of Flat Peaches from Xinjiang
#### 3.3.3 Screening of Common Aromatic Substances in Flat Peaches from Xinjiang  
Although peach varieties have a large number of volatile compounds, some of them have similar aroma characteristics. 2-Hexenal, benzaldehyde, \(\gamma\)-octalactone, phenethyl acetate, and 6-pentyl-2H-pyran-2-one are commonly found in peach varieties (Supplementary Figure S5). To investigate the aroma characteristic of flat peaches (Qingpan, QP; Ruipan 2, R2; Ruipan 4 R4; Wanpan, WP) from Xinjiang, 27 volatile substances with high content were screened as common aromatic substances of flat peaches from Xinjiang (Figure 7). The results showed that the flat peaches possessed similar volatile aroma compounds. 2-Hexenal, decanal, benzaldehyde, \(\gamma\)-decalactone, \(\delta\)-decalactone, and 3-hexenyl acetate were common compounds in the flat peaches, and these compounds had a high concentration. It was confirmed earlier that the concentration of volatile compounds was negatively correlated with the degree of aroma contribution, and higher volatile concentration did not mean a greater impact on the aroma. Thus, the contribution of volatile aroma compounds to odor characteristics was examined by means of calculating the odor activity value (OAV), and the contribution of volatile compounds to the aroma was examined only when OAV \(>\) 1 [79]. Among the 27 volatile compounds in flat peaches, the OAV of 12 volatile aroma substances was more than 1, primarily hexanal, 2-hexenal, nonanal, decanal, benzaldehyde, 2,4-decadienal, dihydro-\(\beta\)-ionone, 6-pentylpyran-2-one, ethyl caprylate,2-hexenyl acetate, \(\gamma\)-decalactone, and theaspirane (Figure 8a). It is easy to see that decanal (OAV 33.00-92.80), theaspirane (OAV 8.80-36.60), \(\gamma\)-decalactone (OAV 11.59-23.67), 2,4-decadienal (OAV 9.48-19.22), dihydro-\(\beta\)-ionone (OAV 4.50-16.89), and hexanal (OAV 3.00-13.05) had the highest levels of OAV. Conversely, the OAVs of nonanal (OAV 1.45-2.65), 2-hexenal (OAV 1.89-4.18), and 2-hexenyl acetate (OAV 1.91-4.04) were lower. Furthermore, as shown in Figure 8b, 2,4-decadienal (0.73-1.48 \(\upmu\)g/kg) and 6-pentylpyran-2-one (0.28-5.76 \(\upmu\)g/kg) were present only in trace amounts but were also considered as strong aroma contributors to the flat peaches from Xinjiang due to their extremely low odor threshold (0.077 \(\upmu\)g/kg, 0.90 \(\upmu\)g/kg). The odor characteristics of the flat peaches might be due to the presence of  
Figure 6: PCA of volatile compounds in dominant fruits from Xinjiang. F: flat peach (_P. persica_ L. _Batsch. var. compressa Bann_), including Qingpan (QP), Ruipan 2 (R2), Ruipan 4 (R4), and Wanpan (WP); N: nectarine (_Prunus nucipersa_ L.), including yellow nectarine (YN) and red nectarine (RN); A: apricot (_Prunus ameniaca_ L.), including Dabaiyou (DBY) and Luopuhongdaike (LH); G: grape (_Vitis vinifera_ L.), including Marselan (MS) and Cabernet Sauvignon (CS). Data from the same laboratory, adapted from [PERSON] et al. (2022) [76], [PERSON] et al. (2022) [77], and [PERSON] et al. (2022) [78]. these 12 volatile compounds. Several studies have shown that C6 compounds of aldehydes (including hexenal and 2-hexenal), lactones (\(\gamma\)-decalactone and \(\delta\)-dodecalactone), and esters (especially hexyl acetate) play a key role in the typical aroma of flat peaches [80]. Hexanal and 2-hexenal render \"fruity\" and \"grassy\" aromas for flat peaches, \(\gamma\)-decalactone is an important source of \"peach-like\" aroma, and benzaldehyde and lactones in synergy to give \"almond\" and \"burnt sugar\" aromas to flat peaches [81; 82]. In the report by [PERSON] et al. (2017) [83], it was also noted that volatile compounds such as linalool, methyl acetate, ethyl acetate, isobutyl acetate, hexanol, and benzene ethanol were closely related to the aroma of flat peaches. Figure 8: The heatmap analysis of the OAVs of selected main volatile compounds found in flat peaches from Xinjiang. **(a)** Heatmap visualization of the analysis of OAVs.