Effects of Cavitation on the Removal and Inactivation of Listeria and Salmonella from the Surface of Tomatoes and Cantaloupe

Abstract

Raw produce has frequently been identified as the source of bacterial pathogens that can cause human illnesses, including listeriosis and salmonellosis. Microbial pathogens may attach and form biofilms on raw fruit surfaces and can be difficult to remove. A cavitation process (formation of bubbles in water) was studied for its effectiveness for removal and inactivation of Listeria monocytogenes and Salmonella Newport from the surfaces of fresh Roma tomatoes and cantaloupes. Individual fruit were separately inoculated with each pathogen, then submerged in a water tank and treated with a bubble flow through an air stone using one airflow rate (0 – 14 liters/min.) for up to 60 sec. As air flow increased, pathogen reduction increased up to 1.2 log CFU/fruit greater than with water alone (no bubbles). Additional pathogen reduction in the tank water (organisms detached from the fruit) was observed with the bubble treatments. Therefore, these bubble streams can be used to enhance the detachment of bacteria from fruit surfaces and to inactivate a proportion of these detached microorganisms. Additionally, recoveries of Salmonella from inoculated Roma tomatoes and cantaloupe were determined for treatment water that contained 50 or 150 ppm sodium hypochlorite. The combination of cavitation and chlorine resulted in greater efficacy of inactivating the pathogen in treatment water, but not in removing this organism from the fruit surfaces. The physical force of a bubble stream on raw produce can effectively reduce and inactivate surface bacteria, and has the potential to reduce antimicrobial chemical and water use in post-harvest packing operations.