## 3 Results and Analysis
### Principal Component Analysis of Aroma Components in 38 Plum Germplasm Resources  
According to Table 3, 138 aroma components of plums from 38 varieties were classified into 16 categories (based on the principle of eigenvalues greater than 3), which captured 81.66% of the total variance, thereby encompassing the majority of the information in the original data. Based on the reported compound aroma thresholds in the existing literature, the aroma values of various aroma components in each variety were calculated, thereby preliminarily determining the characteristic aroma components in the key aroma substances of each variety. Focusing on 71 key aroma components from 38 plum resources, 24 specific aroma components were identified among these key aromas, indicating a significant contribution to aroma characteristics (OAV > 1), as shown in Table 4. Additionally, there were 14 substances with a concentration exceeding 10, and these are considered specific aroma components of key aroma components (Table 5). Among the 38 plum varieties, four specific aroma components, 2-Hexenal, (Z)-3-hexen-1-ol acetate, Academic acid butyl ester, and (E)-2-Hexenal, were present in most plum-specific aroma components. Jihong, Taiyang, and Aitianli fruit had a more prominent OAV for the specific aroma substance 2-Hexenal, with a strong leaf fragrance. The OAV of (E)-2-Hexenal in Gaida was much higher than other varieties, and the pleasant green leaf fragrance and fruit aroma in the fruit were more intense. (Z)-3-hexen-1-ol acetate in Zaoli, Dadanguo, and Xiangjiaoli fruits resulted in a strong banana aroma in their fruit aroma. The strong fruity taste in Jinxiangjiaoli comes from the high OAVs of acetic acid butyl ester, which contribute significantly to its aroma characteristics. Figure 3: Key aroma components in 38 plum fruits at different maturation stages based on OPLS-DA. Results of OPLS-DA (**a**), model cross-validation result (**b**), and VIP values (**c**) of aromatic components in 38 plum resources. The bars displayed in red represent the differential volatile compounds that were identified under the criterion where VIP > 1. In terms of the number of specific aroma components, Dadanguo and Heibali contained the most, with 10 types. Among them, the OAV ranking of the aroma components in Dadanguo fruits was (Z)-3-hexen-1-ol acetate \(>\) 2-hexenal \(>\) acetic acid pentyl ester \(>\) 2-methylbutanoate Butyl \(>\) hexanoic acid methyl ester \(>\) 1-butanol \(>\) 2-methyl-1-butanol \(>\) (E)-2-hexenal \(>\) 1-Octanol \(>\) butanoic acid, mainly presenting with a banana aroma, leaf flavor, and fruit sweet taste. And 1-Octanol is a unique aroma component that is not found in other varieties of plum fruits, with a unique lemon flavor. The main aromatic substance in Heibali was acetic acid butyl ester, (Z)-3-hexen-1-ol acetate, 1-Cyclohexene-2-hexenal and 2,6,6-trimethyl -1-carboxaldehyde; the fruit aroma mainly presents as a strong banana aroma, fruit flavor, leaf aroma, and tropical fruit aroma. The five varieties of plum XY 7-2, Konglongdan, Great Rosa, Richard Early, and Fortune contained the least specific aroma components, all of which had two and did not contain unique aroma components. Among them, the four varieties of XY 7-2, Konglongdan, Great Rosa, and Richard Early had the same specific aroma components, which were (E)-2-hexenal and 2-hexenal, with a fruity and pleasant fruit aroma. The specific aroma components of Fortune were acetic acid butyl ester and (Z)-3-hexen-1-ol acetate, which trigger a strong banana aroma and fruity taste. Xiangiaoli contained the most unique aroma compounds, ethyl acetate, formal acid, and butyl ester, which give its fruit a unique mum-like aroma and sweet fruity taste. The unique aroma component of Hongyang was octanal, with an OAV of 120.06, which has a strong aroma similar to rose and orange peel. Gaida's unique pentanoic acid ethyl ester components give its fruit an apple-like fruity aroma. Jizaofeng's unique 1-octen-3-one ingredient gives its fruit a herbal, mushroom, and earth aroma.