2018 ASHS Annual Conference

Salmonella enterica is the primary foodborne bacterial pathogen of concern, and the target of antimicrobial intervention, for the tomato industry in the United States. The typical commercial tomato dump tank washing practice is a concern as a potential means by which contamination by S. enterica and other harmful microorganisms may be disseminated. Current government regulations and industry performance standards require the presence of sufficient amount of antimicrobial agents in the wash water to mitigate this food safety risk. Presently, maintaining a minimal 150 mg/L of free chlorine in a commercial tomato dump tank is required by the Florida state regulation in the US. While the industry is updating the food safety performance standards, scientific studies are needed to support the development and implementation of science- and risk-based food safety policies. We used grape tomatoes as a model to examine the contamination by Salmonella during a simulated process of tomato washing. Freshly harvested tomatoes were directly obtained from a major US tomato packing operation, and used for generating simulated wash water that matched several key parameters (Turbidity, TDS, and COD) of water used for washing cherry tomatoes by a commercial processor. Tomatoes and field debris were differentially inoculated by strains of different Salmonella serovars distinguishable by their resistance to different antibiotics. Non-inoculated tomatoes were concurrently washed with inoculated tomatoes and debris in the simulated wash water of varying free chlorine levels, with or with pre-washing or post-washing comingling. When inoculated tomatoes and field debris were washed together with non-inoculated tomatoes at free chlorine levels ranging from 5 to 150 mg/L, Salmonella populations on both inoculated tomatoes and field debris were reduced by approximately 2 logs, or approximately 1.2 log higher than that of washing without chlorination. Salmonella was not recovered from the spent wash water at any free chlorine level. Sporadic contamination of non-inoculated tomatoes was observed at lower levels of free chlorine. The contaminating salmonellae originated from both inoculated tomatoes and field debris. These observations indicate that field debris is an important source of cross contamination and removal of field debris prior to washing will reduce the bioburden and source of contamination.