## 3 Results
### Classification of Crabapple Cultivars Based on Fragrance Profiles
Cultivars characterized by the fruit-sweet aroma type were primarily located in the upper region of the second principal component (t [2] > 1), suggesting their aroma profiles were more strongly influenced by ethyl benzoate. Notably, cultivar 17 ('Adams')  
Figure 6: OPLS-DA analysis and model cross-validation based on the relative contents of aroma compounds in 18 crabapple cultivars. Numbers 1–18 represent the following cultivars: 1—Tamlin’, 2—Purple Classic’, 3—Harvest Gold’, 4—Flame’, 5—Kelsey’, 6—Tang-2’, 7—Donald Wyman’, 8—Prairifire’, 9—’Sparkler’, 10—Royal Raindrops’, 11—Radiant’, 12—Purple Prince’, 13—Indian Magic’, 14—Profusion’, 15—Red Jewel’, 16—Spring Snow’, 17—’Adams’, 18—Royalty’. (**A**) OPLS-DA score plot based on the relative aroma contents of the 18 crabapple cultivars. Red, yellow, and blue represent the fruit-almond, fruit-sweet, and mixed aroma types, respectively. (**B**) Model cross-validation results. (**C**) Loading plot showing the contributions of individual volatile compounds to the separation of aroma types along the principal components. Abbreviations: F-A, fruit-almond type; F-S, fruit-sweet type. exhibited an intermediate position near the boundary between fruit-almond and mixed aroma types. Although it contained a relatively high level of ethyl benzoate (17.81 mg/L), its benzaldehyde content (33.52 mg/L) was substantially higher, leading to its initial classification into the fruit-almond aroma type. The intermediate placement of cultivar 17 suggests potential metabolic characteristics shared with the mixed aroma type, warranting further analysis. Cultivars of the mixed aroma type were primarily located on the negative side of the first principal component (t [1] \(<-0.5\)) and were characterized by the concurrent presence of benzyl alcohol, ethyl benzoate, and benzaldehyde. This distribution pattern suggests possible substrate competition or metabolic crosstalk among these compounds within mixed-type cultivars, indicating the simultaneous activity of multiple biosynthetic pathways [32]. The loading plot (Figure 6C) clearly illustrates the contributions of individual volatile components to aroma-type discrimination among fruit-almond (F-A), fruit-sweet (F-S), and mixed cultivars. Specifically, benzaldehyde exhibited a positive loading along the first predictive component (p [1] = 0.25), indicating a significant contribution to the classification of fruit-almond type cultivars. In contrast, ethyl benzoate showed a similar directional trend along p [1] but with a lower loading value, suggesting a relatively weaker influence. Compounds such as nonadecane and ethyl myristate, positioned near the center along the p [1] axis but displaced vertically, appear to have stronger contributions to differentiation along the second predictive component (p [2]). Moreover, volatile components such as diisoamyl, hexacosane, and (E)-3-hexen-1-ol, which cluster towards negative values along p [1], primarily contributed to the aroma profiles characteristic of mixed-type cultivars. These results indicate that benzaldehyde plays an essential role in defining the fruit-almond aroma, while different sets of volatile compounds drive the aroma characteristics of fruit-sweet and mixed types.