# Tree Planting Density and Canopy Position Affect 'Cerasuola' and 'Koroneiki' Olive Oil Quality
## 3 Results and Discussion
### Oil Quality and Minor Compound Composition
The monounsaturated profile of fatty acids is one of the factors that may explain the healthy benefits of olive oil in the Mediterranean Diet [43; 44]. In all of the measured samples, oleic acid was always the predominant fatty acid (70.03-72.47%). Cultivar showed a main effect on fatty acid ratios, with 'Cerasuola' showing a significantly higher UFA/SFA but a lower MUFA/PUFA than 'Koroneiki'. Canopy position also affected fatty acid ratios, with oils from lower layers showing significantly higher UFA/SFA. In 'Koroneiki', higher MUFA/PUFA in the oils from upper layers than in lower layers was due to a decrease of linoleic acid rather than changes of oleic acid. In contrast, an increase of linoleic acid in the oils from upper canopy layers was previously reported in 'Arbequina' and 'Frantoio' and justified by more mature olives [12; 45]. There is no easy explanation for this discrepancy between our results and the previous literature, but a combination of greater light interception and lower crop load of the upper canopy layers in 'Koroneiki' may be in part related to the observed MUFA/PUFA trends. Oleuropein and ligstroside are the most relevant phenolic compounds identified in olive fruit [46]. These substances are hydrolyzed after crushing by the enzyme \(\beta\)-glucosidase, leading to the formation of oleacein and oleuropein aglycon (respectively, 3,4-DHPEA-EDA and 3,4-DHPEA-EA) and oleocanthal and ligstroside aglycon (respectively \(p\)-HPEA-EDA and \(p\)-HPEA-EA), which exhibit a higher lipophilicity and constitute the most abundant phenolic compounds in virgin olive oil [47]. In addition to \(\beta\)-glucosidase, polyphenol oxidase and peroxidase degrade phenolic compounds during the extraction, also shaping the phenolic profile of the oil [48]. Cultivar significantly affected the phenolic composition of the oils (Table 3). 'Cerasuola' presented significantly lower phenol contents compared to 'Koroneiki', except for 3,4-DHPEA-EDA, which was higher in the former cultivar. There was no difference in \(p\)-HPEA-EDA level between cultivars. The phenol content was significantly higher in oils from HD than MD trees, except for hydroxytyrosol that showed higher values in oils from MD trees. Tyrosol was not affected by planting density. Canopy position significantly affected the phenol content in the oil. Oils from fruits in upper layers showed the highest total phenol content due to higher 3,4-DHPEA-EA, 3,4-DHPEA-EDA, and \(p\)-HPEA-EA, but lower hydroxytyrosol. Tyrosol and \(p\)-HPEA-EDA were not affected by canopy position. These results are in accordance with previous studies on 'Arbequina' and 'Frantoio', where canopy position was a determining factor for phenol concentration, increasing with height [12; 45]. Volatile compounds are responsible of the fruity and green aroma of fresh olive oil [49]. These compounds are synthesized during processing from free polyunsaturated fatty acids, through an enzymatic pathway involving two main enzymes, lipoxygenase and hydroperoxide lyase. Lipoxygenase catalyzes the oxygenation of polyunsaturated fatty acids (linoleic and linonic) to produce their corresponding 13-hydroperoxides. Hydroperoxide lyase catalyzes the cleavage of linoleyl and linolenyl 13-hydroperoxides, yielding C5 and C6 aldehydes, the main compounds identified in olive oil [50]. C6 volatiles presented the highest concentration in all of the samples, with (_E_)-2-hexenal being the major volatile compound. (_E_)-2-Hexenal concentration ranged between 13.73 and 0.89 mg kg\({}^{-1}\) for 'Cerasuola' and between 3.58 and 0.47 mg kg\({}^{-1}\) for 'Koroneiki', in oils from HD and MD trees, respectively. In this study, C5 and C6 volatile compounds were affected by cultivar and canopy position. Both families of volatile compounds were highest in oils from 'Cerasuola' and upper layers of the canopy (Table 3). Fruit from upper layers of the canopy of 'Arbequina' were previously reported to have higher volatile compounds concentration than fruit from lower layers after November and a MI higher than 1 [12].