## 2 Results and Discussion
### Comparison of Aroma Compounds of 15 Brands of EVOOs  
As shown in Table 5, the detection frequency of compounds was compared based on the kinds of EVOOs and producing areas. The detection frequency of alcohols in EVOOs of Italy (subtotal: 54) and Greece (subtotal: 58) were higher than that of Spain (subtotal: 39) generally. In particular, there were only five and seven kinds of alcohols in PL and BDS. There was a big difference on that of esters among the samples from these three countries, EVOOs of Spain showed the highest detection frequency (39). Similarly, for the other compounds, there was also the highest detection frequency from samples of Spain. While the ones of aldehydes, ketones, acids, aromatics, and terpen were very close among the samples of these three areas, for the brand of sample, the range of detection frequency was from 41 to 59. The highest one (OL: 59) and the lowest one (BLN: 41) were both from Spain. The impact factor of aroma compound of EVOOs included the cultivar of olive, growing environment, producing technology, storage condition, and so on. From this aspect, these factors might impact EVOO aroma of Spain greatly. Grouping different types of oil is meaningful by flavor because it is an important criterion for EVOO. In the previous studies, cluster analyses were applied to distinguish the different types of edible oil based on their flavor. Sesame oils, soybean oils, and peanut oils could be completely classified using cluster analysis of volatiles [36]. Also, hierarchical cluster analysis showed similarities between EVOO, VOO and LOO (lampante olive oil) samples based on HS-GC-IMS fingerprints [37]. It can be seen from Figure 2, EVOOs were clustered in the heatmap based on their aroma compounds extracted by SPME and SAFE. From Figure 2A, EVOOs of BLN, OL, BDS, OLWL, and YGY had the similar aroma components, all these samples were from Spain except for OLWL. In addition, the flavor was similar between the samples from Italy (ALCF, MNN, AN, and OS) and Greece (DMDN and AGL). From Figure 2B, the aroma compounds of five brands of EVOOs from Spain (PL, OL, BDS, YGY, and BLN) were alike, and they were analogous between the ones from Italy (OS, AN, and MNN) and Greece (DMDN, AGL, and MSWN). Based on these results by SPME and SAFE, the flavor of Spain EVOOs was similar, and that of some of samples from Italy and Greece was alike. It indicated that there was big difference between samples of Spain and the other countries. These results seemed to contradict with that of detection frequency, but it just suggested that the similarity depended not only on the number of compounds but also on the content of ones. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Compounds**} & \multirow{2}{*}{**Threshold [19]**} & \multicolumn{10}{c}{**OAV**} \\ \cline{2-13}  & & **PL** & **BDS** & **OL** & **BLN** & **YCY** & **OUNL** & **OS** & **ALCF** & **MNN** & **AN** & **XBK** & **DMDN** & **MSWN** & **ACL** & **DNLE** \\ \hline Hexanal & 80 & 12 & 11 & 22 & 7 & 25 & 14 & 49 & 19 & 20 & 21 & 50 & 16 & 22 & 20 & 23 \\ (J-2)Hexanal & 420 & 1 & 2 & 1 & 2 & 3 & 3 & 10 & 7 & 6 & 8 & 9 & 7 & 4 & 8 & 15 \\ (J-2)Hexanal acetate & 6.9 & 115 & 296 & 96 & 309 & 135 & 249 & 400 & 159 & 256 & 294 & 200 & 280 & 257 & 493 & 528 \\ (J-3)Hexanal & 1100 & -1 & 1 & -1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 \\ Aortic acid & 500 & 4 & 7 & 4 & 8 & 4 & 1 & 6 & 4 & 6 & 3 & 2 & 1 & 2 & 1 & 2 \\ (J-2)-Heptal & 5 & 55 & 24 & 88 & 11 & 44 & 66 & 81 & 48 & 72 & 57 & 79 & 79 & 57 & 26 & 48 \\ (J-Methyl-5-Heptem-2-one & 1000 & -1 & -1 & -1 & -1 & -1 & -1 & -1 & -1 & -1 & -1 & -1 & -1 & -1 & -1 & -1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Odor activity values (OAVs) of key aroma compounds identified in 15 EVOOs.