## 2 Results and Discussion
The overall volatile assessment can be linked to the threshold levels the different compounds possess. Aldehydes have lower sensory thresholds compared to alcohols [43]; thus, they might be viewed as the largest contributors to the sensory associations of the three studied kernels. Furan and its derivatives usually occur in heat-processed foods and beverages [44]. Moreover, 2-penthylfuran has been identified in a number of foods, i.e., baby food, deep-fried foods, and fruit juice [45], and 2-penthylfuran is the only furan identified in the three kernels, where the hybrid one held the highest %TIC. This compound is known for its distinct fruity flavor and caramel undertones [46]. Figure 3 is a visual presentation of the odor description of each kernel variety based on the VOCs present in them. It can be seen that the hybrid kernel had distinct sweet (32%) and fatty (17%) sensory properties, while the plum kernel had a more fruity (23%), sweet (27%), and fatty (25%) odor description. The apricot kernel also presented a sweet (34%), fatty (19%), and floral (18%) profile. The least recognized odors in the apricot kernel were the ethereal and bitter ones, while in the plum and plum-apricot kernels those were the ethereal and sour ones. The nutty odor was evenly distributed in the hybrid and plum kernels, and more distinct in the apricot kernel. In terms of sensory perception, the plum-apricot kernel is more similar to the apricot kernel than to the plum kernel. This research can be viewed as a pioneering study on the topic of metabolite identification of \"Modesto\" (apricot), \"Stanley\" (plum), and \"Stendesto\" (plum-apricot hybrid) kernels and provide a stepping stone for future evaluations and comparisons. Principal Component and Hierarchical Cluster Analyses of HS-SPME-GC-MS Data  
The chemical composition and volatile content were analyzed using principal component analysis (PCA) and further explored to distinguished separate groups with hierarchical cluster analysis (HCA). As shown in Figure 4A (metabolites), two principal components were generated in the PCA with an eigenvalue greater than 1, accounting for 65.8% (65% for PC 1 and 35% for PC2) of the total variance, whereas, in Figure 4B (VOCs), 59.7% were distributed for PC1 (52.1%) and PC2 (47.9%). Glucaric acid, glucose-1-phosphate, isocitric acid, 2-heptanone, 1-butanol, and acetic acid are positioned most positively, whereas trans-ferulic acid, threonine, (e)-2-heptanal, and 1-pentanol contributed most negatively. As illustrated in Figure 5, the samples can be divided into two clusters for both metabolites (Figure 5A) and volatile compounds (Figure 5B). Figure 3: Odor component distribution in studied fruit kernels (according to [[https://foodb.ca/compounds](https://foodb.ca/compounds)]([https://foodb.ca/compounds](https://foodb.ca/compounds)) descriptor (accessed 1 December 2023). Figure 4: Principal component analysis of kernel samples. Eigenvector loading values of compounds: (**A**) primary metabolites; (**B**) VOCs. Figure 5: Clustering results of kernel samples, shown as heatmap: (**A**) primary metabolites; (**B**) VOCs. The values were normalized by \(\log_{10}\) transformation. The apricot kernel is placed separately from the plum and plum-apricot hybrid kernels. The results from the PCA and HCA were useful to preliminarily distinguish the samples. A correlation analysis of the data is presented in Figure 6. It is assumed that the positively correlated metabolite pairs have similar chemical composition, biological function, and homogeneous characteristics [47]. A positive correlation has been established between n-hexanal and pentanal, n-nonanal, acetic acid, 1-butanol, 2-pentylfuran, 1-penten-3-ol, and (E)-2-ocrenal. Benzaldehyde was positively correlated with sixteen structures, including ethyl benzoate, tridecane, undecane, decane, and benzyl alcohol, among others. Additionally, benzyl alcohol had a positive correlation with fifteen VOCs (2-propanone, 2-furfurral, ethyl benzoate, benzyl acetate, and tridecane, among others).