## 2 Results and Discussion
The C6/LnA aldehyde group of compounds was the most abundant. (_E_)-hex-2-enal was the most important component (averaging 89% of C6/LnA), showing a mean content of 18,518 ng/g oil and a range of 4916-37,643 ng/g oil (Table 2) in good agreement with the average value found for the volatile fractions of the progeny of the Picaul \(\times\) Arbequina cross [30]. This compound might be the main contributor to the aroma of the olive oils produced from the cultivars included in Core-36 due to the high content in the oils, which seems to be a general characteristic of VOO [30], and the relatively low odor threshold (Table 2). The C5/LnA group of compounds exhibited also contents as high as those of the C6/LnA. Among them, pentene dimers showed to be 79% of the C5/LnA content on average. However, they seem to have a minor role in the VOO aroma according to their estimated odor thresholds. Thresholds were estimated (13,500 ng/g oil) from the structurally-related C6-C10 dienes [23]. However, the rest of C5/LnA compounds seem to be important contributors to VOO aroma because of their OAVs. Pent-1-en-3-one and the pent-2-en-1-ols are particularly notable in good agreement with data found by [PERSON] et al. [31]. The content of pent-1-en-3-one in the oils obtained from all of the cultivars of the Core-36 was higher than its odor threshold (Table 2), but its green pungent odor note in the VOO aroma is considered unpleasant [5]. On the contrary, pent-2-en-1-ols provide green fruits odor notes to the oil, which are associated to oils extracted from fresh olives harvested at the optimal ripening stage. Most of the cultivars from Core-36 collection have (_Z_)-pent-2-en-1-ol contents below their threshold concentration, which suggests that, in general, this component is of little significance for the VOO aroma. On the contrary, all of the cultivars included in the Core-36 collection produce oils whose (_E_)-pent-2-en-1-ol contents are higher than their odor threshold (Table 2). The content of esters synthesized through the LOX pathway (LOX esters) present in the oils of the Core-36 collection ranged 29-8414 ng/g oil, and showed an average value of 1447 ng/g oil. Esters present in the oils are very important for the oil commercial grading and from a consumer perspective, as they are responsible for the fruity odor notes in this product. Among them, (_Z_)-hex-3-en-1-yl acetate seems to contribute to VOO aroma (OAV > 1) in nearly 60% of the Core-36 collection (Table 2). However, the contents of hexyl acetate and (_E_)-hex-2-en-1-yl acetate were relevant to VOO aroma in only a few cultivars included in Core-36. Data for the LOX esters largely agree with those observed for the progeny of the cross of Picaul \(\times\) Arbequina [30]. Low concentrations of branched-chain volatile compounds (BC) were found in the oils (Table 2), showing a mean value of 112 ng/g oil and a variability range of 39-521 ng/g oil. However, they could play a relevant role in the oil aroma, except for 2-methyl-butan-1-ol, which was found below its odor threshold in the oils from the Core-36 collection. This BC compound is generally related to the fusty defects of VOO aroma [32]. On the contrary, BC aldehydes 2 and 3-methyl-butanol, situated in the SSW ripe fruit sector as reported by [PERSON] and [PERSON] [13], seem to be important contributors to VOO aroma according to their contents (Table 2). All of the oils from the Core-36 cultivar collection displayed OAV values for these two BC aldehydes higher than one. Terpenes also presented a significant, though low, content in the oils of the Core-36 cultivar collection, limonene being its main representative. The limonene contents ranged in the interval 0-336 ng/g oil and had a mean value of 54 ng/g oil. In general, it seems not to be an important contributor to VOO aroma since just one of the cultivars had an OAV above one for this terpene (Table 2).