Inactivation of Escherichia coli O157:H7 and Natural Microbiota on Spinach Leaves Using Gaseous Ozone during Vacuum Cooling and Simulated Transportation

Abstract

The aim of this study was to integrate an ozone-based sanitization step into existing processing practices for fresh produce and to evaluate the efficacy of this step against Escherichia coli O157:H7. Baby spinach inoculated with E. coli O157:H7 (approximately 10(7) CFU/g) was treated in a pilot-scale system with combinations of vacuum cooling and sanitizing levels of ozone gas (SanVac). The contribution of process variables (ozone concentration, pressure, and treatment time) to lethality was investigated using response-surface methodology. SanVac processes decreased E. coli O157:H7 populations by up to 2.4 log CFU/g. An optimized SanVac process that inactivated 1.8 log CFU/g with no apparent damage to the quality of the spinach had the following parameters: O3 at 1.5 g/kg gas-mix (935 ppm, vol/vol), 10 psig of holding pressure, and 30 min of holding time. In a separate set of experiments, refrigerated spinach was treated with low ozone levels (8 to 16 mg/kg; 5 to 10 ppm, vol/vol) for up to 3 days in a system that simulated sanitization during transportation (SanTrans). The treatment decreased E. coli populations by up to 1.4 log CFU/g, and the optimum process resulted in a 1.0-log inactivation with minimal effect on product quality. In a third group of experiments, freshly harvested unprocessed spinach was inoculated with E. coli O157:H7 and sequentially subjected to optimized SanVac and SanTrans processes. This double treatment inactivated 4.1 to > or = 5.0 log CFU/g, depending on the treatment time. These novel sanitization approaches were effective in considerably reducing the E. coli O157: H7 populations on spinach and should be relatively easy to integrate into existing fresh produce processes and practices.

Comparison of multiple chemical sanitizers for reducing Salmonella and Escherichia coli O157:H7 on spinach (Spinacia oleracea) leaves

“…Vurma, Pandit, Sastry, and Yousef (2009) found that ozone at 935 ppm for 30 min inactivated 1.8 log CFU/g of E. coli O157:H7 with no apparent loss of quality In a separate set of experiments, they treated refrigerated spinach with low ozone levels (5 to 10 ppm) for up to 3 days and decreased E. coli populations by up to 1.4 log CFU/g with minimal effect on product quality (Vurma et al, 2009). Spinach samples exposed to ClO 2 gas for two different treatment times (30 min and 1 h) did not reduce the respective pathogen populations beyond the control water wash. Rodgers et al (2004) reported that ozone reduced E. coli O157:H7 counts on multiple types of produce by more than 5 log CFU/g.…”

Decontamination of Green Onions and Baby Spinach by Vaporized Ethyl Pyruvate

“…Many treatments have been proposed for the decon tamination of fresh produce, including single or combined application of chemical sanitizers, detergents, organic acids, UV light, ozonation, pulsed UV light, high pressure, ionizing irradiation, and several other treatment methods (4,29,30,38,40,41). Currently, chlorinated and nonchlorinated chemical treatments are the most common disinfection methods used in produce processing plants.…”

Regulation of Cell Division, Biofilm Formation, and Virulence by FlhC in Escherichia coli O157:H7 Grown on Meat

“…E. coli O157:H7 has been a constant concern to the food industry. Various antimicrobial sprays and treatment methods have been employed with partial success to actively reduce the bacterial contamination from beef carcasses and food products (9,25,26,30,45,47,55,59). This study observed that three vital cellular processes, cell division, biofilm formation, and pathogenicity, were all downregulated by FlhC.…”