## 3 Results and Discussion
### Relationship between Volatile Compounds and Sensory Attributes  
The sensory attributes have a direct relationship with volatile compounds. A Pearson correlation test was performed to verify the existence of significant correlations between the volatile compounds and the perceived olfactory sensory attributes. The most common positive attribute detected in the olive oils at the olfactory level was dried fruits, present in 98% of the samples, with a median intensity of 3.0. This attribute showed a positive correlation greater than 0.36 with (_E_)-2-hexenal, prop-2-yn-1-yl 2-methylbutanoate, and (_Z_)-3,7-dimethyl-1,3,6-octatriene. Other authors have already described the relationship between (_E_)-2-hexenal and nut aroma [8; 36; 45]. The tomato attribute showed a very significant negative correlation (_p_-value < 0.001) with 1-nonanol (\(-\)0.457), a compound described as mainly associated with fatty sensations [26]. Other authors have shown that 1-nonanol may be associated with the profile in polyphenols, showing a positive correlation with tyrosol and caffe acid [46]. The attribute of cherry showed a very significant positive correlation with octanal (0.573). However, to our knowledge, this relationship has not yet been reported by other authors, with octanal being mainly associated with almond aromas [30] and citrus and fatty sensations [47]. The roscary attribute showed very significant positive correlations (0.522) with the (_E_,_E_)-2,4-heptadien and (_E_)-2-hexenal. This result is identical to that reported by other authors [32], who reported a relationship between (_E_)-2-hexenal and wildflower aroma. The attribute, resinous sensation, showed a significant positive correlation with 1-heptanol and \(\alpha\)-pinene, 0.871 and 0.471, respectively. The relationship between resinous sensations and \(\alpha\)-pinene has been mentioned in the bibliography [34]. Other attributes showed less significant positive and negative correlations (_p_-values between 0.001 and 0.05), as shown in Figure 2.  
Assessment of the Possible Separation of Olive Oils into Sub-Regions, Considering Their Volatile Profile and Sensory Characteristics  
Currently, the Douro Demarcated Region for wine production is divided into three sub-regions, Baixo Corgo, Cima Corgo, and Douro Superior. The wines produced in each of the sub-regions differ. This fact is due to the regions presenting different characteristics, such as temperature, rainfall, and soil, influencing the properties of the wines [48; 49]. To assess whether or not these differences detected in wine were also observed in olive oils, the olive oil characteristics of the referred subregions were evaluated. Since olive trees in the Douro region are mainly found on vineyard borders and are subject to the same edaphoclimatic conditions as the vineyards, the sensory profiles (olfactory and gustatory) and the profiles in volatile compounds of the samples were subjected to hierarchical cluster analysis methods. Thus, this task's main objective was to verify if the olive oils from a given region clustered together or not (Figure 3), demonstrating if the same behaviour as the wines was observed in the olive oils. The results did not show a clear trend of possible groupings of samples from a given region, with olive oils from the same municipalities present in all groups. This situation is acceptable because, although the volatile and sensory profiles may be influenced by soil and climate conditions, these are mainly influenced by the cultivars used and their maturation state. These facts give rise to a profile in fatty acids and different enzyme concentrations, producing volatile compounds that differ from cultivar to cultivar, thus leading to different volatile compounds and different sensory profiles. Other factors affecting the sensory profile are the olive harvesting and olive oil extraction processes that affect the volatile  
Figure 2: [PERSON]’s correlation test (only results with a \(p\)-value \(<\) 0.05 are shown).