Potravinarstvo Slovak Journal of Food Sciences Volume 13 875 No. 1/2019 Potravinarstvo Slovak Journal of Food Sciences vol. 13, 2019, no. 1, p. 875-883 https://doi.org/10.5219/1226 Received: 26 September 2019. Accepted: 11 November 2019. Available online: 28 November 2019 at www.potravinarstvo.com © 2019 Potravinarstvo Slovak Journal of Food Sciences, License: CC BY 3.0 ISSN 1337-0960 (online) STUDY OF CHEMICAL STRUCTURE, ANTIMICROBIAL, CYTOTOXIC AND MECHANISM OF ACTION OF SYZYGIUM AROMATICUM ESSENTIAL OIL ON FOODBORNE PATHOGENS Behrooz Alizadeh Behbahani, Mohammad Noshad, Fereshteh Falah ABSTRACT In this study, chemical composition (gas chromatography-mass spectroscopy), chemical structure (fourier transform infrared spectroscopy) and antioxidant potential (β-carotene bleaching assay and DPPH/ABTS-radical scavenging activity tests) of Syzygium aromaticum essential oil (SAEO) were evaluated. Eugenol (75.11%) was found to be the major compound of SAEO. Eugenol, as the main chemical constituent of SAEO, showed its signature peaks in the wavenumber range of 720 – 1250 cm -1 , ascribing to the C=C region. The antimicrobial activity of SAEO on Escherichia coli, Staphylococcus aureus, Listeria innocua and Pseudomonas aeruginosa were evaluated. The scanning electron microscopy (SEM) was then applied to unravel the antibacterial mechanism of SAEO on E. coli as the most resistant strain and L. innocua as the most sensitive strain. The MTT assay was also used to investigate the cytotoxicity effect of SAEO on human colonic cancer cell lines (HT29 cell line) and the highest cytotoxic effect was observed at 200 mg.mL -1 concentration of SAEO. The SEM micrographs revealed that the SAEO treatment was able to manifestly increase the cell permeabilization and membrane integrity disruption. This means that the entirety of the cell membranes was remarkably affected by the essential oil, which could lead to cytoplasm secretion and subsequent cell death. The data strongly suggest that SAEO had a potential antioxidant, antimicrobial and cytotoxicity activity. Keywords: Syzygium aromaticum; Scanning electron microscopy; Cytotoxic effect; Antimicrobial activity; HT29 cell line INTRODUCTION In recent years, foodborne pathogenic and spoilage bacteria have led to the emergence of one of the important food safety challenges, i.e. new foodborne disease outbreaks (Zhang et al., 2016). It is also worthwhile to note that the lipid oxidation reaction could lead to the formation of potentially toxic side-reaction products capable of threating human health (Zhong et al., 2015). In these contexts, chemical synthetic preservatives have been frequently used in the food industry to suppress microbial growth and lipid oxidation reaction; however, their usages have been a controversial topic, owing to their potential to create health problems (López-Malo et al., 2006; Spickett and Forman, 2015). Therefore, there is a necessity to seek new and safe food-grade antioxidant and antimicrobial agents to amend food shelf-lives. Essential oils (EO) derived from aromatic plants have gained a lot of attention in the food industry not only for their natural origin, but also due to their documented benefits in food and human health. These biologically active compounds confer versatile biological characteristics including antimicrobial, insecticidal, antioxidant, analgesic, anti-tumor, anti- inflammatory, and anti-diabetic effects (Ribeiro-Santos et al., 2017). Syzygium aromaticum L. (clove) is known as an evergreen tree and its commercial products are cloves, clove oil, and oleoresin. The essential oil of S. aromaticum is normally extracted from its stem, unopened buds, and leaves. Clove oil is used in dental formulations, toothpaste, soaps, mouth washes, breath freshner, insect repellent, and cosmetic items owing to different kind of biological properties, such as antibacterial, antifungal, anthelmintic, analgesic, and anti-carcinogenic activities (Srivastava, Srivastava and Syamsundar, 2005). Eugenol is the major chemical compound of S. aromaticum essential oil (SAEO) which its antibacterial and antifungal activities have been reported in the literature (Shokeen et al., 2008; Braga et al., 2007). However, as seen in the literature and to the best of authors’ knowledge, there is no data available indicating the mechanism of antimicrobial activity of SAEO towards pathogenic and spoilage bacteria. This study was therefore aimed to unravel the antibacterial effect of SAEO through mechanistic approaches to provide more insights into the mode of