Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt Comparative evaluation of disinfection mechanism of sodium hypochlorite, chlorine dioxide and electroactivated water on Enterococcus faecalis Zeynep Girgin Ersoy a , Ozge Dinc b,* , Buse Cinar a , Sedef Tunca Gedik a , Anatoli Dimoglo c a Gebze Technical University, Department of Molecular Biology and Genetics, Gebze, Kocaeli, Turkey b University of Health Science, Institute of Health Science, Department of Biotechnology, Istanbul, Turkey c Duzce University, Department of Environmental Engineering, Konuralp Campus, Duzce, Turkey ARTICLE INFO Keywords: Enterococcus faecalis Sodium hypochlorite Chlorine dioxide Electroactivated water Disinfection ABSTRACT The aim of this study is to compare the efficiency of chlorine-based disinfectants, namely, sodium hypochlorite (NaOCl), chlorine dioxide (ClO 2 ), and electroactivated water (EAW), and to investigate their inactivation me- chanisms on a Gram positive, opportunistic pathogen Enterococcus faecalis. Cell viability, damages on membrane integrity and cellular components were examined to reveal underlying mechanisms of the disinfection process. Among three disinfectants, EAW was the most effective one to inactivate E. faecalis in less time with more damage. According to flow cytometry results, EAW destroyed 95.4% of bacteria within 1 min whereas NaOCl and ClO 2 provided 73.9% and 72.6% bacterial inactivation after 20 min of treatment. The rapid increment at conductivity and lipid peroxidation within 30 s of treatment indicates that EAW causes membrane damage much more expeditiously compared to other disinfectants. DNA and protein leakage increased gradually during the treatment with EAW and reached 44.9 and 5.8 μg/ml, respectively. All disinfectants were found as inactivating the bacteria by disrupting cell membrane integrity, unbalancing the ion concentration and damaging the cellular components such as DNA, protein, lipid molecules. It is considered that EAW is more effective due to its superior content including chlorine dioxide, free radicals and ozone besides hypochlorous acid. 1. Introduction Disinfection is a process of deactivation of pathogenic or non-pa- thogenic microorganisms and chemical disinfection is mainly used for this purpose. Chlorine-based technologies are favorable disinfection methods; chlorine gas, hypochlorite solution and other chlorine com- pounds in liquid and solid form are available as chemical agents (EPA, 1999). Sodium hypochlorite (NaOCl), which is the major compound of bleach, is an effective antiseptic substance against microorganisms (McDonnell & Russell, 1999). Chlorine dioxide (ClO 2 ) includes both oxygen and chlorine as oxidizing agents; thus, it is highly effective against bacteria, virus (Morino, Fukuda, Miura, & Shibata, 2011), fungi (Burton, Adhikari, Iossifova, Grinshpun, & Reponen, 2008) and even against spores (Young & Setlow, 2003). Chlorine dioxide has a wide range of application areas such as wastewater and/or drinking water treatment, food and beverage processing (Jonnalagadda & Nadupalli, 2014). Electro activated water (EAW) is produced by electrolysis of a saline solution passing through the electrolysis chamber. When electric cur- rent is applied to the solution, electron exchange takes place between electrodes and water by means of a unipolar electrochemical process. Physical-chemical character of water changes due to the formation of polarization energy on electrodes during the electrolysis process. Inside the electrolysis chamber, negative and positive ions are separated; po- sitive charges are accumulated at the anode surface while negative charges gather at the cathode surface. Consequently, two new products called catholyte and anolyte (namely EAW) are formed in the aqueous solution. Electro activated solution of anolyte has pH values from 7 to 1 and ORP from 0 to +1250 mV, while the catholyte solution has pH values from 7 units to 14 units and ORP from 0 to -950 mV. Anolyte is an aqueous solution with anomalously enhanced electro-acceptor properties. Thus, under unipolar electroprocessing of liquid, reduction products with alkaline reaction are being formed in a diaphragm cell in the cathode zone, and in the anodic zone, there are highly oxidative products with acid reaction. Electro activated water is composed of oxygen gas and many active species such as chlorine, chlorine dioxide and free radicals, while catholyte contains hydrogen gas and sodium hydroxide (Koseki & Itoh, 2000; Kumon, 1997). Due to the presence of a sufficient number of strong oxidants and free radicals, EAW is a solution that has strongly https://doi.org/10.1016/j.lwt.2018.12.041 Received 7 August 2018; Received in revised form 13 December 2018; Accepted 14 December 2018 * Corresponding author. E-mail address: ozge.dinc@sbu.edu.tr (O. Dinc). LWT - Food Science and Technology 102 (2019) 205–213 Available online 15 December 2018 0023-6438/ © 2018 Elsevier Ltd. All rights reserved. T