Enhancement of Antioxidants in Olive Oil by Foliar Fertilization of Olive Trees

Abstract

Oxidative stability (OS) of virgin olive oil is affected by different antioxidants whose levels may be influenced by nutrients availability. Changes in OS of virgin olive oil and antioxidants levels were evaluated according to foliar application of six nutrient‐based treatments: T1 (rich in nitrogen), T2 (rich in boron, magnesium, sulfur and manganese), T3 (rich in phosphorus and potassium), T4 (rich in phosphorus and calcium), T5 (application of T1 and T2) and T6 (application of T1, T2, T3 and T4). The foliar applications were carried out during two successive growing seasons and oils were extracted and analyzed at the end of the experiment (after 2 years). T3 and T6 treatments improved oil stability by increasing the content of antioxidants, while T2 and T4 affected negatively the antioxidant profile of oils. Measured correlations between OS and compositional variables showed that total phenols had the highest value (R = 0.937, p < 0.001), followed by α‐tocopherol (R = 0.775, p < 0.001) and oleic/linoleic ratio (R = 0.625, p < 0.05). These findings suggest that the changing levels of antioxidant compounds, due to fertilization, may be used to obtain oils with the highest quality.

Influence of agroclimatic parameters on phenolic and volatile compounds of Chilean virgin olive oils and characterization based on geographical origin, cultivar and ripening stage

“…Nitrogen nutrition is related to PAL activity because a high availability of nitrogen likely induces protein synthesis rather than the synthesis of phenylpropanoids via PAL, thereby decreasing the o ‐diphenol contents in VOOs and, consequently, antioxidants. Furthermore, high concentrations of nitrogen and potassium have a negative effect because they enhance the PPO activity, which catalyzes the oxidation of o ‐diphenols to produce quinones …”

“…Furthermore, high concentrations of nitrogen and potassium have a negative effect because they enhance the PPO activity, which catalyzes the oxidation of o-diphenols to produce quinones. 10 Table 2 shows the means and standard deviations of the quantified phenolic compounds from the EVOOs produced in the orchards. The total and individual concentrations of phenolic compounds were higher in the orchards located in the Limarí Valley than in Molina (473 vs. 326 mg kg −1 , respectively, in the 2011-2012 season and 493 vs. 208 mg kg −1 , respectively in the 2012-2013 season).…”

“…In fact, some studies have reported that foliar fertilization can modify the quality and chemical composition of olives and influence the quality of virgin olive oil (VOO) . Soil elements also contribute to changes in the concentration of phenols and volatiles…”

“…7 In fact, some studies have reported that foliar fertilization can modify the quality and chemical composition of olives 8 and influence the quality of virgin olive oil (VOO). 9 Soil elements also contribute to changes in the concentration of phenols 10 and volatiles. 11 To our knowledge, there have been no multidisciplinary studies evaluating the agroclimatic parameters and the chemical compounds responsible for the sensory properties of EVOO from various olive tree varieties and orchards with different climates and agricultural practices.…”

Olive oil quality influenced by biostimulant foliar fertilizers

“…However, little is known about the effect of foliar sprays of nutrients on the olive oil quality. Some authors have reported the use of the foliar fertilization and its effect on olive oil quality (Tekaya et al, 2012(Tekaya et al, , 2013Mahmoud et al, 2017). Several works have demonstrated that foliar sprays of biostimulants on olive tree improved oil quality characteristics (Chouliaras et al, 2009), mineral content (Zulaikha, 2013) and fruit yield (Chouliaras et al, 2009).…”