Olive oils have been shown to be more resistant to oxidation than other vegetable fats, mainly due to their fatty acid (FA) profile which is rich in oleic acid and to their high content of antioxidants, principally phenols and tocopherols. This has situated virgin olive oils (VOOs) among the fats of high nutritional quality. However, it is important to stress that the oil’s commercial category (olive oil, virgin olive oil, extra-virgin olive oil), the variety of the source plant, and the extraction-conservation systems all decisively influence the concentration of these antioxidants and the oil’s shelf-life. The present work studied the fatty acid (FA) and phenolic composition and the oxidative stability (OS) of eight olive varieties grown in Extremadura (Arbequina, Cornicabra, Manzanilla Cacereña, Manzanilla de Sevilla, Morisca, Pico Limón, Picual, and Verdial de Badajoz), with the olives being harvested at different locations and dates. The Cornicabra, Picual, and Manzanilla Cacereña VOOs were found to have high oleic acid contents (>77.0%), while the VOOs of Morisca and Verdial de Badajoz had high linoleic acid contents (>14.5%). Regarding the phenol content, high values were found in the Cornicabra (633 mg·kg−1) and Morisca (550 mg·kg−1) VOOs, and low values in Arbequina (200 mg·kg−1). The OS was found to depend upon both the variety and the date of harvesting. It was higher in the Cornicabra and Picual oils (>55 h), and lower in those of Verdial de Badajoz (26.3 h), Arbequina (29.8 h), and Morisca (31.5 h). In relating phenols and FAs with the OS, it was observed that, while the latter, particularly the linoleic content (R = −0.710, p < 0.001, n = 135), constitute the most influential factors, the phenolic compounds, especially o-diphenols, are equally influential when the oils’ linoleic content is ≥12.5% (R = 0.674, p < 0.001, n = 47). The results show that VOOs’ resistance to oxidation depends not only on the FA or phenolic profile, but also on the interaction of these compounds within the same matrix.

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SUMMARY:Although Extremadura is an important producing region of Spanish virgin olive oils, it has not been always known for the high quality of its oils. However, implementation of continuous extraction systems in most of its olive mills has shown a general improvement in the quality of most virgin olive oils, but not in all of them. The aim of the present study was to examine how different variables, such as fruit quality discrimination or payment system, affected the overall quality of virgin olive oils from Extremadura. To do so, a screening experimental design and the corresponding statistical analysis of the collected data were performed. Sixty Extremadura oil mills were evaluated (50.4% of the total) by taking bottled virgin olive oil samples from each of them. Statistical relationships between physicochemical parameters and production process variables were evaluated, showing that only three of them (separation of ground-and tree-harvested fruits, differential payment according to acidity, and extraction process) were significantly correlated with the quality index and acidity of virgin olive oils.

The phenolic composition and content of olive fruit are some of the attributes that determine oil quality. This composition depends on the olive variety, the cultivation system, and the fruit's ripeness. This study considered two olive varieties (Manzanilla and Morisca), under two water regimes (irrigated and rainfed), harvested at three stages of maturation (S1, S2, and S3), over three consecutive campaigns (2011, 2012, and 2013). The accumulation of phenols in the fruit was found to depend only on the stage of ripeness, while the flavonoid and phenylpropanoid contents depended also on the variety and the water regime. Superoxide dismutase (SOD) activity was linked to O 2 - production, which in turn depended on water regime, variety, and stage of maturation (this last being a process involving ROS). The peroxidase (POX) activity seemed only to depend on ripeness, while polyphenol oxidase (PPO) activity varied from year to year as well as presenting a strong ripeness dependence that was in clear coherence with the levels of phenolic compounds that the olives accumulate. All these relationships between the variables and the factors conform a dataset with the structure of a multidimensional array that is difficult to interpret using conventional techniques of statistical analysis. This work takes a novel approach (MultiDimensional Scaling associated with a Partial Triadic Analysis, MDS-PTA) to the analysis of this type of data structure which allows its correct interpretation. The analysis showed that the state of maturation of the olives is the most clearly discriminating factor, far more so than the cultivar, water regime, or year. Thus, the phenols and the total antioxidant activity (FRAP) showed strong clustering, being closely related in all three years studied. The oxidant and antioxidant activities showed a certain tendency to cluster, although in these cases the year also had an influence as a factor, indicating that these parameters depend more on external factors and less on ripeness.