Abstract
Foliar fertilization with selenium (Se) may well be beneficial in increasing the nutritional and qualitative values of food in Se-deficient regions such as the Mediterranean Basin, and may contribute to an increase in drought resistance in plants. The present study has considered detachment force, flesh firmness, pigmentation, fresh and dry weight, and oil content of olive drupes from Se fertilized olive orchards (Olea europaea L.) under drought stress and well-watered conditions. This study has also evaluated the total Se, Se amino acid, phenol, carotenoid and chlorophyll contents of EVOO, plus its oxidative stability against oxidation. While there was no change in the ripening indexes and the production of olives generally, Se application did increase the total Se, Se methionine, phenol, and carotenoid and chlorophyll contents. The higher concentration of these (bio) chemical compounds in EVOO obtained from Se fertilized plants might well suggest enhanced antioxidant activity. Consequently, EVOO obtained from Se fertilized trees possesses a higher nutritional value and, as indicated by the greater oxidative stability against oxidation, longer shelf life. In addition, under water deficient conditions, a higher fresh olive weight corresponds to a higher level of phenol, carotenoid and chlorophyll, and the chlorophyll-to-carotenoid ratio in Se fertilized trees would appear to confirm the positive role of selenium in alleviating damage caused by drought stress conditions.
Highlights
Selenium (Se) is essential for humans since it integrates glutathione peroxidase (GPx) an enzyme that plays an important role in cerebral and reproductive functions (Navarro-Alarcón and López-Martínez, 2000; Rayman, 2000), prevention of cancer and cardiovascular disease (Rayman, 2000; Roman et al, 2014), and the detoxification of heavy metals
The extra-virgin olive oil (EVOO) chlorophyll content was lower under non-drought stressed (NDS) compared to drought stressed (DS) condition, but to carotenoids, Se application increased their amount in the EVOO (Table 3)
While under drought stress the EVOO chlorophyll-to-carotenoid ratio was increased with Se application, in well-watered conditions the ratio decreased with Se application (Table 3)
Summary
Selenium (Se) is essential for humans since it integrates GPx an enzyme that plays an important role in cerebral and reproductive functions (Navarro-Alarcón and López-Martínez, 2000; Rayman, 2000), prevention of cancer and cardiovascular disease (Rayman, 2000; Roman et al, 2014), and the detoxification of heavy metals. Selenium Supplementation on Olive Trees in areas where soil Se levels are low, which is the case in certain parts of Europe (Sager, 2006). The importance of EVOO in these regions coupled with a low level of Se in the area (Spadoni et al, 2007) has forced researchers to develop new methods of increasing the Se concentration of olive oil. Previous studies have demonstrated Se enrichment in EVOO obtained from Se fertilized olive trees (Proietti et al, 2013; D’Amato et al, 2014). The study performed by Torres et al (2014) on EVOO obtained from olive groves in Argentina grown on soil containing Se, has shown the presence of seleno-amino acids such as SeMeSeCys and selenocysteine. Data concerning the effect of these Se compounds on EVOO is scarce, but Zalejska-Fiolka (2000) who demonstrated the anti-oxidative properties of α-tocopherol, SeMet and methionine in olive oil, noted greater anti-oxidative properties in SeMet than in α-tocopherol
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