Efeito antibacteriano da água ozonizada sobre agentes etiológicos de doenças transmitidas por alimentos

Abstract

Fresh vegetables have been frequently identified as a source of bacterial pathogens that can cause foodborne illnesses. Microbial pathogens can adhere and form biofilms on the surfaces of raw fruits and leafy vegetables and can be difficult to remove. Different chemical sanitizers are used for food sanitization, however ozone, due to its oxidative power, has a broad antibacterial effect on a variety of species, including spores, vegetative cells and Gram-positive and Gram-negative bacteria. Ozone is an important tool in vegetable sanitization and plays a relevant role in improving food quality and microbial safety, since the control of spoilage and pathogenic microorganisms is essential throughout the production chain of cultivation, processing, distribution and consumption. The aim of this study was to evaluate the efficacy of ozonated water in the inactivation of Salmonella Enterica serovar Typhimurium (TTC 14028) and Escherichia coli O157:H7 (ATCC 43888) in Sweet Grape tomatoes. To perform the experiments on bacterial viability in suspension and in inoculated tomatoes, the inoculum was prepared in tryptic soybean broth and incubated at 37 °C for 24 hours and adjusted to 106 CFU mL-1. The tomatoes were inoculated by placing 10 units in an autoclaved glass container containing 500 mL of the inoculum of each bacteria and gently shaken for 10 min, and deposited in a biosafety cabinet for 12 hours to facilitate bacterial fixation, subsequently they were removed and air-dried for 10 min in a biosafety cabinet. The ozonation of the water was produced by a commercial ozone generator operating with corona effect and fed by pure oxygen (1.0 L minute-1 ). The gas concentration limited by the calibrated equipment had an O3 flow rate of 17 mg. L-1 . The bacterial suspensions and the inoculated tomatoes were exposed to O3 directly by permanent bubbling at a controlled room temperature of 20ºC. Samples of 0.1 mL were collected at different time periods (0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 minutes), and inoculated on eosin methylene blue agar and xylose lysine deoxycholate agar, incubated at 37°C for 24-48 hours when the colonies were counted. Descriptive statistics of the microbial counts were used for data analysis. The Analysis of Variance (ANOVA) test with Tukey's multiple comparison test was applied to verify possible significant differences between the microbial counts over the time of exposure of the tomatoes to ozonated water. Inactivation of Salmonella enterica serovar Typhimurium (ATCC 14028) and Escherichia coli O157:H7 (ATCC 43888) in suspension was observed in 90 minutes and 120 minutes, respectively. E. coli was more resistant to the action of ozonated water, since its microbial count was zero 15 minutes after exposure of the inoculated tomatoes. Meanwhile, tomatoes contaminated with S. typhimurium needed only 10 minutes of exposure to ozonated water to be considered free of contamination. The application of aqueous ozone in the dynamic mode showed antimicrobial effects on the inactivation rate of bacterial cells in suspension and attached (biofilm) to the surface of the tomatoes.