Phenolic profile (HPLC-UV) of olive leaves according to extraction procedure and assessment of antibacterial activity Oumaima Ghomari*, Fatiha Sounni, Yousra Massaoudi, Jamal Ghanam, Leila Batsoule Drissi Kaitouni, Mohammed Merzouki, Mohammed Benlemlih Biotechnology Laboratory, Faculty of Sciences Dhar El Mahraz, University Sidi Mohammed Ben Abdellah, Fez, Morocco A R T I C L E I N F O Article history: Received 14 March 2019 Received in revised form 6 May 2019 Accepted 20 May 2019 Keywords: Olea europaea Antibacterial activity Extraction methods HPLC Olive leaves Phenolic compounds A B S T R A C T The aim of the present study is to firstly study the effect of the extraction solvents (ethanol, acetonitrile, distilled water), pH, temperature, and the extraction method (maceration, sonication, maceration in two steps) on the flavonoid and phenolic contents of olive leaves. Furthermore, qualitative and quantitative analyzes of phenolic compounds by (HPLC) were performed. Results showed that the extract macerated in two steps by ethanol followed by distilled water of dried leaves showed high contents of phenolic compounds and flavonoids compared to the extracts obtained by the other studied techniques and solvents. On the other hand, the macerated extracts were studied for their antibacterial activity against five pathogenic bacteria (Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Listeria monocytogenes). The results showed a strong antibacterial activity of the same macerated extract in two steps for dried leaves, which could be attributed to its richness in bioactive compounds such as oleuropein. © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction Recently, a number of medicinal plants have been used to treat different diseases in humans and animals [1], due to their richness in bioactive molecules among which we cite flavonoids and phenolic compounds [2]. These compounds are defined as secondary metabolites with strong biological activities such as antioxidant, anti-inflammatory, antimicrobial, hypoglycemic, an- tihypertensive, and antiviral activities [3]. In this context, Olea europaea is widly known as one of the most cultivated tree in the Mediterranean countries where it covers 8 million hectares, nearly 98% of the world's crop [4], which demonstrates the great economic and social importance of this crop in addition to the potential benefits of using its by-products [5, 6]. Olive leaves are an important source of bioactive compounds in comparison to olive oil and fruit [7]. Among the phenolic compounds present in olive leaves, the essential ones are the hydroxytyrosol, tyrosol, catechin, caffeic acid, rutin and oleuropein [8]. The content of these leaves varies according to many factors such as climatic conditions, moisture content, age and variety of the plant, agricultural practices [9], and the extraction procedures used [10]. Thus, extraction is an important and determinative step in the analysis and the use of the cellular bioactive compounds contained in these leaves [7].Therefore, the identification of the appropriate extraction methods is a limiting step to increase the yield of these compounds. In this context, we are interested in studying some parameters that influence the content of phenolic compounds and flavonoids of olive leaves likewise the nature of solvents (80% ethanol, 20% acetonitrile, distilled water), the extraction methods (maceration with a single step, sonication, maceration in two steps with different solvents), pH, temperature, and the state of these leaves (dry or fresh). Then the identification of these compounds such as: coumaric acid, oleuropein, protocatechuic acid, syringic acid, quercetin, gallic acid, ferulic acid, caffeic acid, luteolin, hydrox- ytyrosol, rutin and tyrosol in each extract by high performance liquid chromatography was carried out. Finally the evaluation of the antibacterial activity of different olive leaves extracts against a broad spectrum of pathogenic bacteria was performed in order to explore the relationship between this activity and the content of phenolic compounds and flavonoids of each extract. 2. Methods 2.1. Material Methanol, acetonitrile, phosphoric acid, Folin’s reagent, sodium carbonate (Na2CO3), dimethyl sulfoxide (DMSO), sodium nitrite * Corresponding author. E-mail address: ghomarioumaima@outlook.fr (O. Ghomari). https://doi.org/10.1016/j.btre.2019.e00347 2215-017X/© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Biotechnology Reports 23 (2019) e00347 Contents lists available at ScienceDirect Biotechnology Reports journal homepage: www.else vie r.com/locat e/btre