Effect of Ozone Treatment on Inactivation of Escherichia coli and Listeria sp. on Spinach

Abstract

Abstract:The efficacy of "gaseous" ozone in reducing numbers and re-growth of food-borne pathogens, (Escherichia coli and Listeria spp.), on leafy salads was investigated using spinach. A preliminary in vivo study showed 1-log reduction in six strains of E. coli and two species of Listeria spp. on spinach exposed to 1 ppm ozone for 10 min. A range of ozone treatments were explored to deliver optimal bacterial inactivation while maintaining the visual appearance (color) of produce. Exposure to a higher ozone concentration for a shorter duration (10 ppm for 2 min) significantly reduced E. coli and Listeria spp. viable counts by 1-log and the pathogens did not re-grow following treatment (over a nine-day storage period). Impacts of 1 and 10 ppm ozone treatments were not significantly different. Approximately 10% of the pathogen population was resistant to ozone treatment. We hypothesized that cell age may be one of several factors responsible for variation in ozone resistance. E. coli cells from older colonies demonstrated higher ozone resistance in subsequent experiments. Overall, we speculate that gaseous ozone treatment constitutes the basis for an alternative customer-friendly method to reduce food pathogen contamination of leafy produce and is worth exploring on a pilot-scale in an industrial setting.

Investigation of potential reasons for bacterial survival on ‘ready-to-eat’ leafy produce during exposure to gaseous ozone

“…Interestingly, some individual cells on the leaf surface also survived ozone treatment 304 suggesting that they also have inherent resistance mechanisms. We hypothesised that the 305 survival of the individual bacteria on the leaf surface after ozone exposure is due to ageing or 306 prior exposure to cold (Johnson, 2008;Wani et al, 2015).…”

“…leaf surface bacteria(Wani et al, 2015). Fresh produce typically takes weeks to grow and any 326 cells present on the leaf surface could easily have been present and persisting for a prolonged 327 period.…”

Inactivation of Foodborne Pathogens and Their Surrogates on Fresh and Frozen Strawberries Using Gaseous Ozone

“…Tailing effect was observed with the increase in treatment time. The assumption is that a certain population of bacteria remains resistant to ozone due to the adaptation of microorganisms to certain stresses (Van Boekel, 2002;Wani et al, 2015Wani et al, , 2016. Additionally, the flow rate in the present study was slow (1 L/min) which may limit the gas exchange on the strawberries' surfaces.…”

“…Studies on baby spinach showed 1-log reduction of E. coli and Listeria spp. after being exposed to 10 ppm ozone gas for 2 min (Wani et al, 2015). As ozone sensitivity is commodity dependent, it is important to establish optimal application conditions for each food commodity (Karaca, 2010).…”

Antimicrobial Particle-Based Novel Sanitizer for Enhanced Decontamination of Fresh Produce

“…To address safety and spoilage issues of fresh produce, a number of decontamination methodologies for fresh produce have been reported (10,11). Current chemical treatments such as chlorine, peroxyacetic acid, hydrogen peroxide, quaternary ammonium, and ozone are effective in reducing the microbial load in wash water but have limited efficacy for inactivation of bacteria on fresh produce surfaces (1-to 2-log reduction) (12)(13)(14)(15). This limitation is due to nonspecific consumption of sanitizers upon reactions with the food matrix (16).…”