Salmonella inactivation and cross-contamination on cherry and grape tomatoes during washing in simulated commercial wash water

Authors: BOLTEN, SAMANTHA - University Of Maryland; GU, GANYU - Virginia Tech; Luo, Yaguang - Sunny; VAN HAUTE, SAM - University Of Maryland; Zhou, Bin; Millner, Patricia; MICALLEF, SHIRLEY - University Of Maryland; Nou, Xiangwu

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2019
Publication Date: 11/6/2019
Citation: Bolten, S., Gu, G., Luo, Y., Van Haute, S., Zhou, B., Millner, P.D., Micallef, S.A., Nou, X. 2019. Salmonella inactivation and cross-contamination on cherry and grape tomatoes during washing in simulated commercial wash water. Food Microbiology. 87:103359. https://doi.org/10.1016/j.fm.2019.103359.
DOI: https://doi.org/10.1016/j.fm.2019.103359

Interpretive Summary: Salmonella contamination is the primary food safety concern for the fresh tomato industry. Research data on the effectiveness of chlorine on preventing and mitigating Salmonella contamination is urgently needed to update fresh tomato processing guidelines. In this study, ARS scientists and collaborators investigated the efficacy of Salmonella inactivation during a simulated wash process using hypochlorous acid as sanitizer on fresh tomatoes. The major findings of this study are that Salmonella carried by field debris (inedible plant materials co-harvested with tomatoes) were inactivated very inefficiently, and the debris can serve as a source for Salmonella cross-contamination during washing. This study provides new information to help the fresh tomato industry to reduce risks of Salmonella contamination, and to update it’s tomato processing guidelines.

Technical Abstract: Washing in chlorinated water is widely practiced for commercial fresh tomato processing. While known as an effective tool for mitigating food safety risks, chlorine washing could also represent an opportunity for spreading microbial contaminations under sub-optimal operating conditions. The aim of this study was to evaluate the inactivation of salmonella and the potential for Salmonella cross-contamination onto tomatoes when washed at different levels of free chlorine with different sources of initial contamination. Commercially harvested tomatoes (cherry and grape varieties) and associated inedible plant materials (debris) were differentially inoculated with kanamycin resistant (KanR) or rifampin resistant (RifR) Salmonella strains, and washed together with uninoculated tomatoes in simulated packing house dump tank wash water. Washing in water with 25-150 mg/L free chlorine reduced Salmonella inoculated on tomato by approximately 2-3 logs, while the magnitude of the reduction was poorly correlated with chlorine concentration in the tested range. Under the same washing conditions, the reduction of Salmonella inoculated on debris was in most cases < 1 log, never exceeding 1.65 logs. In the presence of 25-150 mg/L of free chlorine, sporadic cross-contamination on uninoculated tomatoes was detected when washed together with tomatoes and debris differentially inoculated with Salmonella strains at high population density. The cross-contamination predominately (11/12) originated from inoculated debris. Debris as a potential source of microbial cross contamination should be further investigated.