Characterization of wild and centenarian olive trees for their valorization = Caracterización de acebuches y olivos centenarios para su valoración
Área de conocimiento
The species Olea europaea L. is constituted by two varieties, the cultivated one - the olive tree, O. europaea subsp. europaea var. europaea; and the wild form - the wild olive tree or oleaster, O. europaea subsp. europaea var. sylvestris. These varieties were differentiated during the domestication process, and from the cultivated form a high number of cultivars evolved over the years. In the last decades, due to the crop intensification a few number of well adapted or productive cultivars have been used in the new olive plantations, leading to the abandonment of minor cultivars and to a loss of the olive genetic heritage. Nevertheless, in the last years, a niche of more informed and demanding consumers appeared, searching for olive oils that combine their richness in health promoters, like polyphenols, tocopherols and sterols, with a differentiated sensory profile. In this context, the general objective of this work was to characterize genetically and morphologically oleander populations and centenarian olive trees from the northeast of Portugal, as well as, to chemically and sensory evaluate the extracted oils, aiming the selection of plant specimens with the purpose of future valorization. Three oleander populations from Alijó, Moncorvo and Vila Nova de Foz Côa (VNFC) regions and 28 specimens of centenarian olive trees, grown in Mirandela region (Suçães), some of them from known cultivars (cvs. Lentisca, Madural, Rebolã, Redondal, Verdeal and Verdeal Transmontana) were characterized. The comparison of genetic diversity, structure and phylogenetic relationships within and among the oleaster and centenarian plants were studied using microsatellite markers. High genetic diversity was observed in both oleaster and centenarian plants, with no differences between them in the amount of genetic diversity. Population structure analysis suggests genetic differentiation between the studied varieties. The oils of the three oleaster populations were evaluated considering their fatty acids, tocopherols, phenols and sterols composition. Globally, the chemical composition was very similar to that of olive oils and fulfilled the legal limits for virgin olive oil classification. Oleic (68.9-70.6%) was the main fatty acid, followed by palmitic (14.2-14.7%) and linoleic (7.87-9.88%). Tocopherol ranged between 263 and 503 mg/kg oil, being α-tocopherol the most representative (higher than 90%). High levels of total sterols were observed, from 1742 to 2198 mg/kg of oil, with a profile similar to olive oil. The contents of phenolic compounds were greater than 603 mg/kg and 14 compounds were identified. Ligstroside derivatives and oleuropein aglycon (and derivatives) were the most abundant ones. This work demonstrated that the chemical composition allowed discriminating the different oil populations, showing that oleaster oils could be valorized, being a good source of bioactive compounds. Also, in order to select specimens as potential producers of differentiated olive oils with high levels of phenolic compounds, and so, as possible candidates for multiplication or breeding programs, 28 centenarian trees were studied during four crop years (2014-2017). Thirteen phenolic compounds were identified and quantified, being hydroxytyrosol and tyrosol secoiridoids the predominant ones Fifty per cent of the evaluated trees produced olive oils that could be labeled as "Olive oil polyphenols contribute to the protection of blood lipids from oxidative stress”. In particular, olive oils produced from trees nº24, 25 and 26 had, consistently, high phenolic contents, during the four studied crop years, being, therefore, good candidates to be used in breeding programs as producers of olive oils rich in phenolic compounds. Six minor autochthonous olive cultivars produced from centenarian trees were also studied and characterized, aiming the selection cultivars that allowed producing differentiated olive oils. In this context, the quality parameters, sensory profile and oxidative stability were evaluated for two crop years (2016 and 2017); and, tocopherols contents and fatty acids composition, were determined during five consecutive crop years (2013-2017). All the oils produced were classified as Extra Virgin Olive Oils. Oils obtained from cv. Redondal presented the highest oxidative stability (OS), total phenols contents, and C18:1/C18:2 ratios. In contrast, cv. Madural oils presented the lowest levels of OS and C18:1/C18:2 ratios, strengthen the role of fatty acids levels in the OS. Finally, oils from cv. Verdeal had the lowest levels of total phenols. Regarding the sensory evaluation, the usual sensory notes of tomato, apple, dried fruit, fresh herbs, tomato leaves and cabbage were predominant in most cultivars, nevertheless some attributes were specific like banana and kiwi (cv. Madural) as well as cherry and apricot (cvs. Lentisca and Madural). The amounts of tocopherols, considering all years, followed the order cvs. Lentisca (456 mg/kg olive oil)» Redondal (404 mg/kg olive oil) ˃ Madural (311 mg/kg olive oil) » Rebolã (269 mg/kg olive oil) ˃ Verdeal Transmontana (206 mg/kg olive oil) » Verdeal (179mg/kg olive oil). Concerning the fatty acids profile, monounsaturated fatty acids allowed distinguishing different groups taking into account their relative abundance: cvs. Redondal (82.1%) ≈ Verdeal Transmontana (81.7%) > Lentisca (79.1%) > Verdeal (77.4%) > Rebolã (74.3%) > Madural (71.2%). The obtained results pointed out that, the oils extracted from the different cultivars, had a high consistent composition. Using different statistical tools, namely principal component analysis, discriminant analysis and hierarchical grouping analysis, it was possible to discriminate olive oil according to the cultivar and the crop year. Cvs. Redondal and Lentisca showed the best results for the main evaluated parameters. Finally, the results obtained contributed to enhance the scarce knowledge of olive heritage, and may be further used to support the selection of olive cultivars for new plantations, based on their potential to produce oils with a more favorable chemical, sensory and bioactive profile, in which concerns the nutritional and oil quality points of view.
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