Quantitative Determination of the Main Phenolic Compounds, Antioxidant Activity, and Toxicity of Aqueous Extracts of Olive Leaves of Greek and Spanish Genotypes

Abstract

Olive leaves are rich in phenolic compounds, which give them antioxidant properties that are associated with a lower incidence of disease. Therefore, the aim of this work was to determine the phenolic content, antioxidant activity, and toxicity of the aqueous extracts of olive leaves of the main Spanish and Greek cultivated and wild genotypes. For these purposes, ‘Picual’ and ‘Arbequina’ leaves from Spain and ‘Koronoeiki’ and ‘Kalamon’ leaves from Greece were collected, as were wild olive leaves from both countries. The aqueous extracts of these genotypes were analyzed by HPLC-DAD, and the DPPH·, ABTS·+ Folin–Ciocalteu, and Microtox® methods were also used. ‘Picual’ had the highest oleuropein values, followed by wild olive leaves from both countries and ‘Arbequina’. The latter was reflected in the antioxidant activity measured by DPPH· and ABTS·+, which positioned the leaves of ‘Arbequina’, ‘Picual’, and the wild genotypes as having the most antioxidant activity. As expected, these leaves also had the highest total phenol content, as measured by Folin–Ciocalteu. Regarding the inhibition of the bioluminescence of Aliivibrio fischeri of the aqueous leaf extracts measured by Microtox®, the EC5015 ranged between 11.82 and 82.50 mg/mL, demonstrating similar behavior to other herbal infusions.

Antioxidant and Anti-Diabetic Properties of Olive (Olea europaea) Leaf Extracts: In Vitro and In Vivo Evaluation

“…Orak et al, 2019 [ 42 ], studied the phenolic compounds in 12 olive leaf genotypes and showed that oleuropein was the primary component for all genotypes. These findings were in line with the findings of Martínez-Navarro et al [ 40 ], who revealed that the oleuropein showed the highest value in the ‘Picual’ genotype compared to other genotypes. Zhang et al [ 43 ] identified thirty-two phytochemical compounds in olive leaf extracts using high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry, including seventeen flavonoids, five iridoids, two hydroxycinnamic acids, six triterpenic acids, one simple phenol and one coumarin.…”

“…Additionally, the scavenging activity of OLE may be able to stop the potentially hazardous “NO” radical-initiated oxidation chain reaction [ 39 ]. Martínez-Navarro et al, 2023 [ 40 ], revealed that olive leaf extract (OLE) is an effective antioxidant in biological systems, preventing oxidative stress based on its scavenging activity against RNS, with an IC 50 of 48.4 ± 6.8 mg/mL. The nitric oxide scavenging activity showed a lower IC 50 than DPPH and reducing power, which suggests that the NO - radicals are more sensitive against the phytochemical molecules of OLE.…”

In vitro biological evaluation and in silico insights into the antiviral activity of standardized olive leaves extract against SARS-CoV-2

“…Reviewing the previous literature; the major phyto-constituents in olive leaves was reported such as oleuropein, hydroxytyrosol, verbascoside, luteolin, luteolin-7- O -glucoside, and apigenin-7- O -glucoside [ 33 ]. Olive leaves extract is usually standardized to its oleuropein content usually up to 20% (w/w), flavonoids which constitutes up 1.8% (w/w), of which 0.8% is luteolin 7-glucoside [ 34 ], while Apigenin-7-O-glucoside was found in concentration up to 2.05 mg/g olive leaf extract [ 35 ]. Hydroxytyrosol in addition was previously determined in olive leaf extracts in concentration up to 2.28 mg/100 g leaf extract [ 36 ], and verbascoside content up to 3.97 mg/g olive leaf extract [ 35 ].…”

Valorization of Olive Leaves through Polyphenol Recovery Using Innovative Pretreatments and Extraction Techniques: An Updated Review

“…Olive leaves are also rich in lignins, constituting up to 35.72% of their composition [21]. The surfaces of olive leaves contain a high quantity of triterpenes, especially oleanolic and maslinic acids, known for their antimicrobial, antitumor, anti-inflammatory, and anti-HIV activities [22] The diversity of bioactive compounds depends on different factors, e.g., the genotype [23,24] and the cultivar [25][26][27], climate variations, collection season, etc. For example, the highest polyphenol content was detected in different cultivars (Arbequina, Manzanilla, and Picual) during the summer season.…”