## 3 Results
### Odor-Based Classification of Volatiles and OAV Analysis  
The odor characteristics of the major volatile compounds facilitated the classification of the aromas from 18 crabapple cultivars into six scent note groups: floral, fruity-almond, fatty, fruity-sweet, woody, and spicy. Figure 4A,B depict the total content and relative proportions of each volatile class across the cultivars. The scent categories of fruity-almond, fruity-sweet, and woody emerged as the most dominant, collectively comprising over 77% of the total volatile composition among the cultivars. Heatmap analysis (Figure 4C) revealed distinct, cultivar-specific patterns in the concentrations of 25 principal aroma compounds. For instance, benzaldehyde and ethyl benzoate were found in significantly higher concentrations in 'Royal Raindrops', whereas nonadecane was notably enriched in 'Royalty'. Linalool was present at elevated levels in 'Purple Classic', and benzyl benzoate was detected exclusively in 'Profusion' and 'Royalty'. Ethyl hexadecanoate was ubiquitous across all cultivars, showing no significant variation in concentration. It is crucial to recognize that the presence of a volatile compound does not necessarily correlate with its olfactory impact, as the odor threshold plays a pivotal role  
Figure 3: Major volatile compounds associated with floral scent released from 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**) Relative contents of 25 major volatile compounds across the 18 cultivars. (**B**) Proportions of the 25 major volatile compounds in the 18 cultivars. (**C**) Comparison of the trends between relative contents and sensory evaluation scores. Data represent means and standard errors of three biological replicates. in scent perception. The Odor Activity Value (OAV) is commonly employed to quantify the contribution of aromas; typically, an OAV greater than 10 signifies a major aroma contributor, while an OAV above 1 suggests a contributing component [27]. Table S4 indicates that benzaldehyde displayed an exceptionally high OAV in certain cultivars. In 'Royal Raindrops', the OAV for benzaldehyde reached 39,387.75, with similarly high values in 'Prairifire' (11,718.42) and 'Profusion' (13,887.90), indicating a substantial influence on the aromas of these cultivars. Similarly, ethyl benzoate demonstrated high OAVs across multiple cultivars, peaking at 1917.22 in 'Royal Raindrops'. Although benzyl alcohol displayed a lower OAV in comparison, it still achieved 171.94 in 'Royal Raindrops', significantly surpassing the threshold for a key aromatic contribution (OAV > 10). These three aromatic compounds--benzaldehyde, ethyl benzoate, and benzyl alcohol--are notably prevalent in the most fragrant cultivars, highlighting their essential role in differentiating aroma profiles and establishing them as crucial chemical markers of crabapple floral scent. In contrast, compounds such as alkanes (e.g., heneicosane) are commonly found among cultivars (Figure 4C); however, their extremely high odor thresholds result in minimal contributions to the overall scent [28]. Consequently, they are not considered key aroma constituents. Figure 4: Odor classification and contents of 25 major volatile 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—Adam’s, 18—Royalty’. (**A**) Relative contents of six groups of major volatile compounds. (**B**) Proportions of the six groups of major volatile compounds.