This study investigates the feasibility of sequentially applying sanitation technologies - vacuum, gaseous ozone, and pressurized gases - to leafy green produce to overcome external and internal contamination with E. coli O157:H7. The development of this approach involves: <ol>
<li> adapting existing vacuum-cooling technology for freshly harvested produce to include a sanitization step involving repressurization with gaseous ozone;
<li> determining the kinetics of E. coli O157:H7 inactivation in leafy green produce in relation to the treatment variables; and
<li> monitoring the viability of E. coli O157:H7 during ozone treatment and refrigerated storage of fresh produce.</ol>
Ozone is a potent sanitizer that is well-suited for use with fresh produce. Results of this project may provide the fresh produce industry with a critical decontamination step that can be incorporated into exiting production and processing lines, potentially reducing the health risks associated with sporadic contamination of fresh produce with E. coli O157:H7.
The preliminary experiments will involve the use of an elaborate ozone treatment vessel located in the investigators\' biosafety level-2 facility. Processing variables to be tested include: vacuum level; vessel pressure after ozone introduction; ozone concentration; treatment time; average temperature; and product loading. Preliminary studies will be conducted on diffusion of ozone into various locations within the treatment chamber. A sampling manifold will be installed to draw gas samples from multiple locations when different product loads are tested. Product/vessel volume ratio will be optimized to make sure all leaves are exposed to the sanitizer. If needed, a slow tumbling of the product within the vessel during the treatment will be applied. In all cases, E. coli O157:H7 will be counted (or detected, if the bacterial population is uncountable) in produce before and after treatment, as well as during storage.
This study will identify treatment conditions sufficient to eliminate E. coli O157:H7 in fresh produce, at realistic contamination levels, while maintaining product quality and integrity. It will also optimize an ozonation process for scale-up and incorporation into pre-packaging treatments of fresh produce.