Original article Antimicrobial efficacy of gaseous chlorine dioxide against Salmonella enterica Typhimurium on grape tomato (Lycopersicon esculentum) Siriyupa Netramai, 1 * Thitisilp Kijchavengkul, 1 Veesuda Sakulchuthathip 1 & Maria Rubino 2 1 Division of Food Technology, School of Interdisciplinary Studies, Mahidol University, Kanchanaburi Campus, Kanchanaburi 71150, Thailand 2 School of Packaging, Michigan State University, Lansing, MI 48824-1223, USA (Received 12 February 2016; Accepted in revised form 18 June 2016) Summary The aim of this study was to investigate the effects of gas level and treatment condition on antimicrobial efficacy of ClO 2 gas against Salmonella enterica Typhimurium on grape tomato (Lycopersicon esculentum). Grape tomatoes were dip-inoculated with inoculum of S. enterica Typhimurium TISTR 292 (ATCC 13311) (9.79 Æ 0.39 log CFU mL À1 ) and allowed to dry before treatments. The pre-inoculated samples were exposed to 0.15–0.85 mg of ClO 2 gas, for up to 58 min. The treatments at 4 and 25 °C resulted in population reductions of S. enterica Typhimurium of up to 3.95 Æ 0.22 and 7.37 Æ 0.39 log CFU per fruit, respectively. The population reduction results were used to construct statistical models to predict efficacy of ClO 2 gas. The second-order equations for treatments at 4 and 25 °C had R 2 of 0.87 and 0.95, respectively, and indicated that efficacy of ClO 2 gas was significantly influenced by ClO 2 gas level, exposure time and treatment temperature. Keywords Chlorine dioxide, grape tomato, response surface methodology, Salmonella enterica Typhimurium, vapour-phase decontamination. Introduction The currently increasing demand for minimally pro- cessed food products is strongly influenced by con- sumers’ health-conscious lifestyles. Fruits and vegetables are being incorporated into each meal in a larger portion to increase minerals and fibre intakes. However, there also have been increasing numbers of reported foodborne outbreaks, caused by consump- tions of contaminated fresh and/or fresh-cut produce (Sandhya, 2010; CDC 2014). Precautionary steps such as sorting, cutting and trimming, as well as, cleaning and sanitising, harvested produce have been imple- mented to discard the inedible, diseased and/or con- taminated portions, thus reducing the population of spoilage or pathogenic micro-organisms found in raw materials. Chlorine dioxide (ClO 2 ) is a strong oxidant that could potentially be used to sanitise these com- modities (Bartz et al., 2009; Olaimat & Holley, 2012). Currently, only aqueous ClO 2 is approved by Food and Drug Administration (FDA) as disinfectant for fruits and vegetables (FDA 2012). Antimicrobial efficacies of ClO 2 , both in the liquid and gas forms, against many important pathogens have been studied and documented (Han et al., 2001b; Finnegan et al., 2010; G omez-L opez, 2012). Some studies also reported the adverse effects caused by ClO 2 treatment on the produces’ qualities and/or appearances (G omez-L opez et al., 2008; Shin et al., 2011; Jooken et al., 2013; Singh et al., 2002). In recent years, several studies are focused on the use of ClO 2 gas in vapour-phase decontamination (Wu & Rioux, 2010; Netramai et al., 2012; Trinetta et al., 2013). The possibility of using the treatment as part of the hurdle technology has also been explored (Goodburn & Wal- lace, 2013; Olanya et al., 2015). The sanitising treat- ments could potentially be applied during the processing of raw material as mentioned earlier, or during storage and distribution of the final product, as the antimicrobial gas introduced into the package’s headspace (G omez-L opez et al., 2009; Shin et al., 2011; Netramai et al., 2012; Lee et al., 2015). In cases where the application of moisture is not necessary, the *Correspondent: Fax: +66 34 585 070; e-mail: siriyupa.net@mahidol.ac.th International Journal of Food Science and Technology 2016, 51, 2225–2232 doi:10.1111/ijfs.13209 © 2016 Institute of Food Science and Technology 2225