## 2 Results
### Principal Component Analysis (PCA)  
Principal component analysis (PCA) was used as a multivariate tool to detect correlations between all the breeding lines and VOCs. PC1 and PC2 accounted for 17.2% and 15.3% of the total variation, respectively (Figure 3). In the loadings plot (Figure 3B), most of the alcohols, aldehydes, and esters are on the right side of the PC2 axis, making up the 1 st and 4 th quadrants. The breeding lines correlating to these are BL-9, BL-7, BL-4, BL-20, BL-35, BL-12, BL-6, BL-1, BL-43, BL-28, BL-26, and BL-30. Since aldehydes, alcohols, and esters are the chemical classes usually associated with melon aroma and flavor [21; 22], this suggests that these lines produce fruit with good odor and flavor properties. Some of the major compounds present in these quadrants are eucalypt, benzaldehyde, carveol, citral, geranylacetone, limonene, cinnamaldehyde, \(\upalpha\)-calacorene, benzothiazole, \(\upbeta\)-ionone, and benzyl alcohol. However, the 4 th quadrant of the loadings plot (Figure 3B) indicatesthe presence of two sulfurous and four acidic compounds, which suggests an intricate relationship between sensory properties and breeding lines.  
Considering the 2 nd and 3 rd quadrants, which lie on the left side of the PC2 axis (Figure 3), we found that only a few volatile compounds associate with the breeding lines present in these two quadrants (BL-19, BL-25, BL-22, BL-34, BL-24, BL-17, BL-14, BL-21, BL100 (10), BL-8, BL-18, BL-40, BL-36, and BL-33). Methoxy-phenyl-oxime was associated with these lines; this compound is known to have anti-bacterial properties [86] and has been reported to be present in bamboo shoots [37; 38], but has only been reported in muskmelons once [63]. Further research on its sensory and/or antibacterial properties should therefore be conducted.  
Among all the breeding lines, the highest average VOC content was observed in BL-30 (13,973.07 \(\upmu\)g/kg FW) (Table S1). 3-Phenylpropanol (1823.52 \(\upmu\)g/kg FW), geranylacetone (1191.69 \(\upmu\)g/kg FW), and 3-decen-1-ol (1070.61 \(\upmu\)g/kg FW) were found in the highest quantities in BL-30 (average content > 1000 \(\upmu\)g/kg FW) (Table S3). 3-Phenylpropanal is known for its fruity, spicy, and floral aroma [87], and geranylacetone exhibits a fruity, tropical aroma and flavor and is also known for its anti-microbial properties [70]. The highest number of volatiles was observed in BL-20 (77), with benzaldehyde (1628.10 \(\upmu\)g/kg FW) followed by geranylacetone (1223.77 \(\upmu\)g/kg FW) exhibiting the highest average contents (Table S3).  
The lines characterized here had more aldehydes and alcohols than esters, which implies that the melons were not fully mature, since the presence of esters is mostly associated with ripe, mature melons whereas aldehydes are mostly associated with immature fruits [35]. This is in accordance with the color readings (Table 2), where BL-4, BL-7, BL-11, BL-15, BL-28, BL-30, BL-33, BL-34, and BL-40 were associated with lightness and green color along with high contents of aldehydes and alcohols (Figure 3A,B).  
BL-33, BL-7, BL-4, BL-24, BL-36, BL-9, BL-14, BL-25, BL-26, BL-6, BL-28, and BL-22 were positively associated with the three main sugars along with total sugars (Figure 4). Although BL-17 and BL-12 did not have total sugar values associated to them, BL-17 was positively correlated to glucose and fructose, while BL-12 had more sucrose. Future breeding programs could focus on selecting lines with good sensory properties, i.e., high aroma and high sugar content, and with compounds having anti-microbial and health beneficial properties.  
Figure 3: Principal component analysis of 28 melon breeding lines displayed according to their chemical classes. (**A**) corresponds to the scores plot. (**B**) corresponds to the loadings plot and the codes indicate the volatile compounds, as displayed in Table 3.