Survival of pathogens on work-in-process fresh-cut produce ingredients

Survival of pathogens on work-in-process fresh-cut produce ingredients

Jan. 1, 2024 - Dec. 31, 2025

2024CPS02

USDA - ARS

$300,872.00

Xuetong Fan, Ph.D.
USDA - ARS

Joshua B. Gurtler, Ph.D., Bryan T. Vinyard, Ph.D.

Work-in-Process (WIP) fresh-cut produce ingredients, often as minor components of finished products (salads), are held in containers for various times before being utilized. The objective of this proposed research is to evaluate the survival/growth of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella on WIP ingredients and transfer of pathogens between WIP ingredients and holding containers. The survival of cold-adapted L. monocytogenes, E. coli O157:H7 and Salmonella spp. will be evaluated on nine selected WIP ingredients in holding containers as a function of holding time, temperature, pathogen inoculation level, and washing with sanitizers. Also to be determined are innate natural antimicrobials and microbiota, which may serve as indicators for the presumed variation among WIP ingredients in terms of the pathogen survival on WIP ingredients during holding time. The transfer probability of pathogens from WIP ingredients to holding containers and consequent contamination potential of new batches of WIP ingredients from re-used containers will be quantified. Models will be developed to predict the survival of pathogens on WIP ingredients and containers, and to evaluate the risk of cross-contamination between WIP ingredients and holding containers. The study will be beneficial to the industry in understanding the risk associated with WIP ingredients.

Technical Abstract

Work-in-process (WIP) fresh-cut ingredients as components of final retail products (salads), are often stored in large plastic bins for varying short lengths of time before being mixed with other components, such as lettuce, to form the final consumer products.  Although there have been studies dealing with survival of human pathogens on various fresh produce items, including shredded carrots, cabbage and lettuce, studies on survival of WIP fresh-cut ingredients during holding time are limited and the WIP ingredients step is often missed in the hazard analysis. In addition, there is no clarity regarding the chance of pathogen transfer from WIP ingredients to the surface of holding containers and subsequent survival of pathogens on containers, and cross-contamination of WIP ingredients when containers are re-used. The objective of the proposed study is to evaluate the survival of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella spp. on selected WIP ingredients during holding time, as well as pathogen transference potential onto containers. WIP ingredients (carrot, green cabbage, red cabbage, kale, radish, Brussel sprout, green onion, broccoli stalk, and baby spinach) inoculated at 2 levels (2 and 6 log CFU/g) of 4-strain cocktails of cold-adapted L. monocytogenes, E. coli O157:H7 and Salmonella spp. will be stored at 4, 8 12 and 16°C for up to 6 days. The WIP ingredients will be washed with 20 ppm chlorine (pH 6.5) and 80 ppm peracetic acid before and after the holding period to study the effects of sanitization. Populations of both uninjured and injured pathogens will be determined every 2 days. Based on earlier studies, it is predicted that pathogen (especially Listeria) populations will decline on shredded carrots and cabbage during holding time, presumably due to the presence of natural antimicrobials and/or competitive microbiota.  Therefore, total mesophilic aerobic bacteria, Enterobacteriaceae, lactic acid bacteria, aerobic psychrotrophs, and yeast and mold counts will be monitored on the WIP ingredients using appropriate media, along with natural antimicrobials on the surface of (and inside) WIP ingredients, using HPLC and spectrophotometric methods. The profile and populations of microbiota and native antimicrobials may be used to predict the survival of pathogens. The potential transfer of pathogens onto holding containers will be determined by placing WIP ingredients with various inoculation levels into WIP ingredients containers, followed by tracking pathogen populations on the container surfaces. The contaminated WIP ingredients containers will be re-used to hold WIP ingredients to study the transfer of pathogens from the containers to WIP ingredients. Statistical models will be fit to predict: the growth/survival of pathogens as functions of holding temperature, holding time, level of contamination, sanitization wash, and type of WIP ingredients; and relationships among pathogen growth, antimicrobials, and native microbiota. The risk (probability) of cross-contamination between WIP ingredients and containers will be estimated as the proportion of observed containers in which contamination is transferred to non-inoculated WIP ingredients. The study will identify conditions that prevent pathogen growth and transference observed in the lab to help the industry establish a standardized commercial scale risk approach for managing WIP fresh-cut produce ingredients.