# Natural Variation of Volatile Compounds in Virgin Olive Oil Analyzed by HS-SPME/GC-MS-FID
## 3 Results and Discussion

Table 2: Content of the volatile compounds (ng/g oil) in the oils from the WOGC cultivar subset and percentaje of cultivars with odor activity values (OAV) higher than 1 for each volatile compound. the latter (Figure 2, light gray ellipses), which correspond to the C5/LnA alcohols, carbonyls, and pentene dimers, respectively. The group of C5/LnA alcohols is the closest to the C6 compounds, which would indicate a greater metabolic proximity and would support the hypothesis that C5/LnA alcohols would be the first products formed from the homolytic branch of the LOX pathway, which involves the activity of a LOX protein forming an alkoxy radical from a polyunsaturated fatty acid [33], parallel to the pentene dimers formation but in different ways, and finally oxidized enzymatically to C5/LnA carbonyls. Moreover, it was found previously that the pentene dimer content is not related to the contents of the C5/LA carbonyls (5C-14, 5C-15) or alcohol (5C-16), suggesting that pentene dimers are only synthesized from LnA [35]. Accordingly, those compounds are located in Figure 2 far from the group of pentene dimers. On the other hand, the esters grouped together, overlapping the space of the C6 compounds, where the main precursors of esters are located [(hexan-1-ol (6C-9) and (Z)-hex-3-enol (6C-7)]. This partial disconnection from the LOX pathway mainstream could be due to the limitation of alcohol production during the oil extraction process, mainly due to the inactivation of ADH activity during VOO production, as previously demonstrated [36]. The PCA approach explains the associations between the different classes of volatile compounds in the olive collection subset, and allows us to distinguish those olive cultivars that are especially rich in some compounds (Figure 3). The first factor explains 19.87% of the variance, whereas the second factor explains 16.54%. Similar values were found when evaluating the content of the main volatile compounds in the oils of the Core-36 nuclear collection from the WOGC [35], and the progeny of the cross of cultivars Picual and Arbequina [29]. Cultivars producing oils with high contents of C6/LnA aldehydes are situated in the fourth quadrant of the plot, while those producing oils with high contents of C5/LnA are located opposite in the second quadrant. This distribution allows the selection in the fourth quadrant of those cultivars producing oils characterized by high contents of C6/LnA aldehydes,  
Figure 2: Factor analysis. Position of the volatile compounds in the oils from the WOGC cultivar subset on the first two factors using the normalized Varimax method. LOX esters, as well as BC aldehydes, which might act synergistically to provide green fruity odor notes. Most of the compounds included in those volatile classes are situated in sectors 'green fruit' and 'ripe fruit' of the statistical sensory wheel [20]. Therefore, it is possible to select cultivars from the germplasm collection subset whose oils have a prevailing green aroma, such as those cultivars located in the bisector of the first quadrant. Table 2 shows those volatile compounds which present contents in the cultivar oils that make them major contributors to the oil aroma (OAV > 1). However, other volatile compounds contribute to the oil aroma of only a certain number of cultivars. A new PCA was carried out considering as variables those volatiles with OAV higher than one in more than 5% of the cultivars, thus truly contributing to the aroma of the oil (Figure 4). Most of them are considered desirable for VOO aroma, except for hexan-1-ol (6C-9), pent-1-en-3-one (5C-1), and pent-1-en-3-ol (5C-4). The latter give unpleasant sensations [9; 20; 34]. Factors 1 and 2 explain 43% of the data variation, quite similar to what was found for the Core-36 nuclear collection from the WOGC [35], and the progeny of the cross of cultivars Picual and Arbequina [29]. When using as variables those volatile compounds with OAV higher than one in more than 5% of the cultivars, the cultivars are distributed mainly along the Factor 1 axis (Figure 4b).