Phenolic extracts of clove (Syzygium aromaticum) with novel antioxidant and antibacterial activities

IntroductionClove (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.MethodsEthyl 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.ResultsEthanol 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′azino bis-(3-ethylbenzthiazoline-6-sulfonic acid), β-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 β-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 μg/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.ConclusionsUsing 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.