Development and validation of an HPLC‐DAD method for determination of oleuropein and other bioactive compounds in olive leaf by‐products

Abstract

BACKGROUND Oil mills could benefit by preparing their own aqueous extracts from olive leaves. Accordingly, the present study aimed to measure the bioactive compounds richness of such extracts, especially oleuropein. A water‐based microwave extraction procedure was developed and a selective and precise high‐performance liquid chromatography with diode array detection (HPLC‐DAD) method was validated for the determination of oleuropein and others bioactive compounds from olive leaves. RESULTS The water solubility of oleuropein was determined to be 9.5 g L−1. The extraction procedure was optimized in terms of power, olive leaf weight/water volume ratio and time of extraction, and the results revealed that 2 mg mL−1 and a microwave irradiation at 800 W for 30 s resulted in the greatest efficiency. Oleuropein was determined by the new validation method, which showed good linearity (r2 = 0.996), precision (% relative standard deviation < 10%), recovery (118.6%), and limits of detection (17.48 mg L−1) and quantification (21.54 mg L−1). Good correlation (r2 = 0.979) was obtained between oleuropein of the olive leaf extracts determined by HPLC‐DAD and by UV‐visible spectrophotometry. CONCLUSION A simple extraction method was developed and validated to obtain aqueous extract from olive leaves by microwave extraction, determining for the first time oleuropein water solubility. Validation of the method showed that oleuropein in olive leaves could be quantified when it is at least 1% of dry weight by means of HPLC‐DAD. UV‐visible spectrophotometry can be useful in oil mills because it enables the content of oleuropein and other bioactive compounds content to be determined in situ in such leaf aqueous extracts. © 2020 Society of Chemical Industry

Oleuropein Degradation Kinetics in Olive Leaf and Its Aqueous Extracts

“…Aqueous extracts of olive leaves were prepared according to Martínez-Navarro et al (2021) [4] with 25 mL of distilled water and 50 mg of olive leaf powder. The mixture was extracted in a domestic microwave oven (MS-2819W; Saivod, Madrid, Spain) at 800 watts for 30 s. For the liquid kinetics, 1 L of aqueous extract was prepared, which was stored under the conditions described in Section 2.2.…”

“…Traditionally, these waste products are burned or used for animal feed. However, the olive leaves are rich in polyphenols, bioactive compounds with beneficial health effects, which should be used as secondary raw materials for pharmaceutical, cosmetic and food sectors [ 3 , 4 ]. These health benefits are due to the composition in bioactive compounds, mainly oleuropein.…”

Determination of the Variability of Bioactive Compounds and Minerals in Olive Leaf along an Agronomic Cycle

“…Leaf samples of age 0, 1 and 2 positioned at North, South, East and West have been pool together for each tree reaching 120 leaves, which were dried in the dark for seven days and stored at freezing temperatures (−20 • C) until use. The frozen and dried leaves were ground in a knife mill (ARES FML-2000, Barcelona, Spain), sieved (500 mesh) and subjected to microwave extraction using water as an extractant according to the methodology described by Martínez-Navarro et al (2021) [6]. All extractions were performed in triplicate.…”

“…The analysis was carried out according to the method in Martínez-Navarro et al (2021) [6]. Aqueous extracts, pre-filtered by nylon syringe filter 0.22 µm (Labbox, Barcelona, Spain), were injected into an Agilent 1200 high-performance liquid chromatograph (Palo Alto, CA, USA) equipped with a diode-array detector (Agilent G1315D) coupled to a ChemStation, version B.03.01 (Agilent, Palo Alto, CA, USA) data-processing station.…”

“…Oleuropein has been identified as the most suitable precursor of hydroxytyrosol, which has a wide range of biotical and pharmacological uses, as a potential therapeutic, antithrombotic, cardioprotective, antitumor, microbicidal or anti-inflammatory agent [3][4][5], for example. There is a great potential to obtain aqueous extracts rich in bioactive compounds from olive leaves due to the water-solubility of these compounds, making this waste very interesting for its transformation in the oil mills themselves [6].…”