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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #384065
Research Project: Characterization and Mitigation of Bacterial Pathogens in the Fresh Produce Production and Processing Continuum

Location: Environmental Microbial & Food Safety Laboratory

Title: The influence of organic load and free chlorine on Salmonella cross-contamination of tomatoes in a model flume system

Author
item BERTOLDI, BRUNA - University Of Florida
item BARDSLEY, CAMERON - University Of Florida
item PABST, CHRIS - University Of Florida
item BAKER, CHRISTOPHER - University Of Florida
item GUTIERREZ, ALAN - University Of Florida
item DE, JAYSANKAR - University Of Florida
item Luo, Yaguang - Sunny
item SCHNEIDER, KEITH - University Of Florida

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2021
Publication Date: 9/15/2021
Citation: Bertoldi, B., Bardsley, C.A., Pabst, C.R., Baker, C., Gutierrez, A., De, J., Luo, Y., Schneider, K.R. 2021. The influence of organic load and free chlorine on Salmonella cross-contamination of tomatoes in a model flume system. Journal of Food Protection. https://doi.org/10.4315/jfp-21-212.
DOI: https://doi.org/10.4315/jfp-21-212

Interpretive Summary: Tomatoes have been implicated in numerous foodborne illness outbreaks. The presence of sufficient amounts of free chlorine in the tomato wash water is considered as a preventive control to ensure food safety. However, research data gaps exist regarding the survival and spread of Salmonella (a harmful bacterium) as impacted by chlorine concentration and organic load. Researchers from USDA and University of Florida collaborated to evaluate the effect of chlorine concentration and organic matter load on the cross-contamination of Salmonella during wash operation. Results indicate that when the contamination level of Salmonella is less than 10,000 cells per tomato, a chlorine concentration of 25 ppm is sufficient to prevent Salmonella spread via tomato wash water. These findings will benefit the tomato industry in establishing science- and risk-based food safety regulations and industry standards.

Technical Abstract: The process of washing tomatoes in dump (flume) tanks has been identified as a potential source of cross-contamination. This study's objective was to assess the potential for Salmonella enterica cross-contamination at various inoculation levels at the presence of 0 and 25 mg/L free chlorine (HOCl) and organic matter. Uninoculated tomatoes were introduced into a laboratory-based model flume containing tomatoes inoculated with a cocktail of five rifampicin-resistant Salmonella enterica serovars at 4-8 Log CFU/tomato in water containing 0 or 25 mg/L HOCl and 0 or 300 mg/L chemical oxygen demand (COD). Uninoculated tomatoes were removed from the water at after 5, 30, 60, 120 s and were placed in bags containing tryptic soy broth supplemented with rifampicin and 0.1% sodium thiosulfate. Following incubation, enrichments were plated on tryptic soy agar supplemented with rifampicin and xylose lysine deoxycholate agar to determine the presence of Salmonella. HOCl and pH were measured before and after each trial. The HOCl in water containing 300 mg/L COD significantly (P=0.05) declined in each trial, most likely due to the increased demand for the oxidant. Higher inoculum levels and lower HOCl concentrations were (P=0.05) significant factors that contributed to increased cross-contamination seen in this study. When HOCl levels were at 25 mg/L, no cross-contamination occurred under all conditions when inoculum levels were at 4 Log CFU/tomato. When the inoculum was increased to 6-8 Log CFU/tomato, cross-contamination was observed, independent of COD levels. The results from this study show that the currently required sanitizer level for flume water may be higher than necessary and warrants re-evaluation.