Research paper Phenolic extracts of clove (Syzygium aromaticum) with novel antioxidant and antibacterial activities Mohamed F. Abo El-Maati a , Samir A. Mahgoub b , Salah M. Labib a , Ali M.A. Al-Gaby a , Mohamed Fawzy Ramadan a, * a Agricultural Biochemistry Department, Faculty of Agriculture, Zagazig University, Zagazig 44519, Egypt b Agricultural Microbiology Department, Faculty of Agriculture, Zagazig University, 44519 Zagazig, Egypt A R T I C L E I N F O Article history: Received 9 June 2015 Received in revised form 18 February 2016 Accepted 18 February 2016 Keywords: Natural antioxidants Antiradical activity Phenolic compounds Pathogenic bacteria Electron microscope Clove Antibacterial A B S T R A C T Introduction: Clove (Syzygium aromaticum) is a rich source of bioactive compounds. The goal of this study was to test different extracts of clove in terms of their phenolic contents, their antioxidant potential and their antibacterial action against pathogenic bacteria. Methods: Ethyl acetate, ethanol (80%) and water were used to extract bioactive phytochemicals from clove. Recovered extracts were studied in terms of total phenolic compounds, total flavonoids, antioxidant properties and antibacterial activity. Scanning and transmission electron microscopy was applied to study the effect of ethanol extracts on the morphology and membranes of tested bacterial cells. Results: Ethanol and water were the best solvents for extracting phenolics (ca. 230 mg GAE g 1 extract) but water was the best solvent for extracting flavonoids (17.5 mg QE g 1 extract). Antioxidant potential of clove extracts was estimated using DPPH  (1,1-diphenyl-2 picrylhydrazyl), ABTS  + 2, 2 0 azino bis-(3- ethylbenzthiazoline-6-sulfonic acid), b-carotene-linoleic bleaching assay and ferric reducing antioxidant power (FRAP). Ethanol and water extracts showed comparable antioxidant activity to the synthetic antioxidant tert-butylhydroquinone (TBHQ). The DPPH  radical quenching activity varied from 25.3 to 91.4%, while clove extracts showed ABTS  + scavenging activities from 49.4 to 99.4%. Clove extracts inhibited the bleaching of b-carotene wherein the order of decreasing activity was water > ethanol > ethyl acetate extracts as compared with TBHQ. Extracts showed strong antibacterial activities against Staphylococcus aureus ATCC 6538, Listeria monocytogenes Scott A, Salmonella enteritidis PT4, Serratia marcescens and Escherichia coli ATCC 8739. Clove extracts exhibited antibacterial activities against the growth of S. aureus and E. coli in concentration range from 50 to 100 mg/mL. The results indicated that the extracts with stronger antibacterial capacity also had higher phenolic content. Scanning and transmission electron microscopy showed that ethanol extract damaged the morphology and membranes of tested bacterial cells. Conclusions: Using cloves and their extracts in food or pharmaceutical products may be an effective antioxidant and antimicrobial control strategy. Data from this study might be used for developing natural preservatives and bioactive agents with health promoting activities. ã 2016 Elsevier GmbH. All rights reserved. 1. Introduction Medical plants, herbs, spices and oilseeds are rich sources of natural antioxidants such as flavonoids, curcumanoids, tannins, terpenoids and lignans. There is growing interest in characterizing and extracting natural bioactive compounds from these sources and using them in different food and pharmaceutical applications [1–3]. Solvents with different polarities were used to extract phenolics and bioactive compounds from plant materials [4,5]. Extraction yield depend on the solvent polarity and the technique of extraction [6,7]. Water, aqueous ethanol (70%), aqueous methanol (50%) and acetone are used commonly in the extraction of bioactive compounds [8]. For extracting flavonoids from tea, aqueous ethanol was better than methanol and acetone [9]. For extracting tea catechins, water was better solvent than aqueous methanol and aqueous ethanol [10]. Clove (Syzigium aromaticum L., family Myrtaceae) is considered to have an enormous potential as a food preservative against spoilage and pathogenic bacteria. Commercial cloves are the dried and unexpanded flower buds which are used as a condiment or * Corresponding author. E-mail address: hassanienmohamed@yahoo.com (M.F. Ramadan). http://dx.doi.org/10.1016/j.eujim.2016.02.006 1876-3820/ã 2016 Elsevier GmbH. All rights reserved. European Journal of Integrative Medicine 8 (2016) 494–504 Contents lists available at ScienceDirect European Journal of Integrative Medicine journal homepa ge: www.elsev ier.com/e ujim