## 2 Results and Discussion
### Volatile Compounds  
HS-SPME coupled to GC-MS was utilized to characterize the VOCs in _Masnjaca_, _Krvavica_ and _Lececino_ VOOs. Identified C\({}_{6}\) VOCs in investigated olive oils were mainly aldehydes such as hexanal, (_E_)-hex-2-enal and (_Z_)-hex-3-enal (Table 2). These C\({}_{6}\) compounds derive from the lipoxygenase (LOX) catalyzed oxidation of linoleic or \(\alpha\)-linolenic acids (Scheme 1) and were the main VOCs detected in all the tested olive oils. Different values of identified C\({}_{6}\) aldehydes in the samples could be due to different acyl hydrolase activity and consequently good or poor availability of free polyunsaturated fatty acids. 3-Ethyloct-1,5-diene is derived from linoleic acid (Scheme 1). _Krvavica_ oil was characterized by the highest level of hexanal, _Lececino_ oil by (_E_)-hex-2-enal and (_Z_)-hex-3-enal was predominant in _Masnjaca_ oil. According to [PERSON] _et al._[4], the level of each C6 compound depends on cultivar, which is confirmed by our results. The level of C\({}_{5}\) compounds (such as pent-1-en-3-one, pentan-3-one and (_E_)-pent-2-enal) was found to be lower in comparison to the C6 compounds. The percentage of pent-1-en-3-one that is positively correlated with bitter taste of VOO [7], in _Krvavica_ oil was approximately two times lower than in _Leccino_ oil and three times lower than in _Masnjaca_ oil (Table 2). Additionally, in contrast to _Masnjaca_ oil, _Krvavica_ oil did not contain (_E_)-pent-2-enal and _Leccino_ oil did not contain pentan-3-one. Several hydrocarbons such as \(\alpha\)-copaene, _trans_-\(\beta\)-ocimene and two isomers of 3-ethyloct-1,5-diene, were detected in the investigated olive oils. _trans_-\(\beta\)-Ocimene was identified only in _Masnjaca_ and _Krvavica_ oils, whereas, \(\alpha\)-copaene and 3-ethyloct-1,5-diene were detected in all the oils. \begin{table}
\begin{tabular}{l l c c c c c c c c c c} \hline \hline \multirow{3}{*}{**No.**} & \multirow{3}{*}{**Compounds**} & \multirow{3}{*}{**RI**} & \multicolumn{3}{c}{_Masnjaca_} & \multicolumn{3}{c}{_Krvavica_} & \multicolumn{3}{c}{_Leccino_} \\  & & & & & **Area [\%]** & & & **Area [\%]** & & & **Area [\%]** \\ \cline{3-11}  & & & & **Min** & **Max** & **Mean \(\pm\) SD** & **Min** & **Max** & **Mean \(\pm\) SD** & **Min** & **Max** & **Mean \(\pm\) SD** \\ \hline
1. & Isoprene & \(<\)900 & 3.3 & 3.6 & \(3.5\pm 0.15\) & 1.6 & 1.7 & \(1.7\pm 0.05\) & 1.1 & 1.2 & \(1.2\pm 0.05\) \\
2. & Ethyl acetate & \(<\)900 & 1.1 & 1.2 & \(1.2\pm 0.50\) & 0.8 & 0.8 & \(0.8\pm 0.00\) & - & - & - \\
3. & Pent-1-en-3-one & \(<\)900 & 5.6 & 6.2 & \(5.9\pm 0.30\) & 2.0 & 2.0 & \(2.0\pm 0.00\) & 4.2 & 4.5 & \(4.4\pm 0.15\) \\
4. & Pentan-3-one & \(<\)900 & 5.2 & 6.1 & \(5.7\pm 0.45\) & 3.8 & 3.9 & \(3.9\pm 0.05\) & - & - & - \\
5. & (_E_)-Pent-2-enal & \(<\)900 & 0.6 & 0.6 & \(0.6\pm 0.00\) & - & - & - & 0.3 & 0.3 & \(0.3\pm 0.00\) \\
6. & (_Z_)-Hex-3-enal & \(<\)900 & 21.9 & 25.0 & \(23.5\pm 1.50\) & 15.0 & 15.0 & \(15.0\pm 0.00\) & - & - & - \\
7. & Hexanal & \(<\)900 & - & - & - & 8.8 & 9.4 & \(9.1\pm 0.30\) & 1.1 & 1.1 & \(1.1\pm 0.00\) \\
8. & (_E_)-Hex-2-enal & \(<\)900 & 27.6 & 28.9 & \(28.3\pm 0.65\) & 41.6 & 44.4 & \(43.0\pm 1.40\) & 73.4 & 74.0 & \(73.7\pm 0.30\) \\
9. & 3-Ethyloct-1,5-diene & & 939 & 13.8 & 14.4 & \(14.1\pm 0.30\) & 3.3 & 4.2 & \(3.8\pm 0.45\) & 7.1 & 7.5 & \(7.3\pm 0.20\) \\
10. & 3-Ethyloct-1,5-diene & & 997 & 10.7 & 10.9 & \(10.8\pm 0.10\) & 3.3 & 4.1 & \(3.7\pm 0.40\) & 5.1 & 6.0 & \(5.6\pm 0.45\) \\
11. & _trans_-\(\beta\)-Ocimene & 1054 & 0.6 & 0.7 & \(0.7\pm 0.05\) & 1.9 & 2.5 & \(2.2\pm 0.30\) & - & - & - \\
12. & \(\alpha\)-Copaene & 1380 & 1.6 & 2.2 & \(1.9\pm 0.30\) & 0.8 & 1.1 & \(1.0\pm 0.15\) & 0.0 & 0.1 & \(0.1\pm 0.05\) \\
**Total identified** & & & (92.0\%–99.8\%) & & (82.9\%–89.1\%) & & (92.3\%–94.7\%) \\ \hline \hline \end{tabular}  
* RI = retention indices on HP-5 MS column; Min. = minimal percentage; Max. = maximal percentage; mean. = average percentage; SD. = standard deviation.  
\end{table}