Olive Leaf Addition Increases Olive Oil Nutraceutical Properties.

Imen Tarchoune,Cristina Sgherri,Angela Zinnai,Mokhtar Zarrouk,Jamel Eddouzi,Mike Quartacci

doi:10.3390/molecules24030545

Abstract

The aim of the present research was to study the effects of olive leaf addition (0 and 3%) on the major antioxidants and the antioxidant activity of Neb Jmel and Oueslati olive oils. Olives and leaves of the two Tunisian varieties were harvested during the 2016/2017 crop season. Both leaves and oils were characterised for their concentrations in phenolics, tocopherols and antioxidant power. Other parameters such as free acidity, peroxide value, chlorophyll and carotenoid concentrations were also taken into consideration. Compared to Oueslati, the Neb Jmel oil showed a lower free acidity (50%) and peroxide value (5.6-fold), and higher chlorophyll (1.6-fold), total phenolics (1.3-fold), flavonoid (3-fold) and oleuropein derivative (1.5-fold) concentrations, in addition to an increased antioxidant activity (1.6-fold). Leaf addition promoted a significant increment in total chlorophyll, α-tocopherol and phenolics in both varieties, above all in Oueslati oil, due to a higher abundance of bioactive constituents in the corresponding leaves. In particular, chlorophyll and carotenoid concentrations reached values twice higher than in Neb Jmel leaves, and flavonoids and oleouperin derivatives were three-fold higher. This prevented the oxidation and the formation of peroxides, reducing the peroxide value of the fortified oil to the half. The results provide evidence on the performance of the Tunisian Neb Jmel and Oueslati varieties, showing that their oils present a chemical profile corresponding to the extra virgin olive oil category and that, after leaf addition, their nutritional value was improved.

Highlights

In the Mediterranean area, the olive tree is so economically important that oliviculture is one of the most widespread agricultural activities
According to the definitions and standards established by the International Olive Oil Council [22], the classification of virgin olive oil into different categories depends on its chemical, physical and sensory parameters, among which the degree of acidity and the peroxide value (Table 1) are the most used
(44.3 μg/g) concentrations, highlighting the role that the addition of chlorophyll could have had in the oxidative stability of the olive oil. This can further explain the difference with the results reported by Malheiro et al [17] concerning the peroxide value, as in their study olive leaf addition did not affect the chlorophyll content

Summary

Introduction

In the Mediterranean area, the olive tree is so economically important that oliviculture is one of the most widespread agricultural activities. It is estimated that about 8 million ha are cultivated with olive trees [1,2]. In Tunisia, an area of 1.7 million ha is covered by olive trees, which results in the production of more than 4% of the global olive oil amount. Due to the 170,000 tons produced per year, Tunisia is the fourth largest producer and exporter of olive oil in the world [3]. The nutritional and health-promoting effects of olives and olive oils are more and more recognized [4]. It is well known that olive oil is a potential antioxidant [5,6,7] showing

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