Survival of Salmonella enterica and shifts in microbial community as impacted by tomato wash water particulate size and chlorine treatment

Authors: VAN HAUTE, SAM - UNIVERSITY OF MARYLAND; Luo, Yaguang - Sunny; BOLTEN, SAMANTHA - UNIVERSITY OF MARYLAND; GU, GANYU - ORISE FELLOW; Nou, Xiangwu; Millner, Patricia

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2020
Publication Date: 2/28/2020
Citation: Van Haute, Sam, Luo, Y., Bolten, S., Gu, G., Nou, X., Millner, P.D. 2020. Survival of Salmonella enterica and shifts in microbial community as impacted by tomato wash water particulate size and chlorine treatment. Food Control. 90:103470. https://doi.org/10.1016/j.fm.2020.103470.
DOI: https://doi.org/10.1016/j.fm.2020.103470

Interpretive Summary: Commercially grown tomatoes are cleaned of field debris by washing them in deep channels with flowing water at a packing house after field harvest. This washing is the first step to prepare tomatoes for packaging, or any subsequent processing before shipment to distribution and retail outlets. Commercial tomato packing house wash water thus contains harvest debris of various sizes, but the impact on food safety of this debris in the wash water is unknown. Even very small particles of debris in the wash water may provide protection for bacterial pathogen survival. In collaboration with the tomato industry, USDA Scientists investigated the formation of particulates from these debris and their potential role in harboring and protecting harmful bacteria such as Salmonella during the wash process. Results demonstrate that particulates larger than 330 µm could serve as a vector in spreading bacteria from contaminated to un-contaminated tomatoes. Thus, preventing harvest debris from entering the tomato packing house wash tank represents a great opportunity to mitigate food safety risks. This research provides information for the fresh produce industry to develop science- and risk-based food safety practices.

Technical Abstract: Particulates of harvest debris are common in tomato packinghouse dump tank, but their role on food safety is unclear. This study investigated the survival of Salmonella enterica and the shifts in microbial community as impacted by particulate size and interaction with chlorine treatment. Particulates suspended in grape tomato wash water range widely in size, but the largest contribution comes from particles of 3 to 20 µm. Filtration of wash water through 330 µm, applied after 100 mg/L free chlorine (FC) wash, reduced surviving cell counts by 98%. The combination of filtration (at 330 µm or smaller pore sizes) and chlorinated wash also significantly altered the bacterial community, with the surviving microbiome shifting toward Gram-positive and spore producers. When tomatoes and harvest debris inoculated with differentially tagged Salmonella were washed in 100 mg/L FC for 1 min followed by filtration, only cells originating from harvest debris survived, with 85 and 93% of the surviving cells associated with particulates larger than 330 and 63 µm, respectively. This suggests that particulates suspended in wash water can protect Salmonella cells from chlorine action, and serve as a vector for cross-contamination.