Modeling of Free Chlorine Consumption and Escherichia coli O157:H7 Cross‐Contamination During Fresh‐Cut Produce Wash Cycles

Abstract

Controlling the free chlorine (FC) availability in wash water during sanitization of fresh produce enhances our ability to reduce microbial levels and prevent cross‐contamination. However, maintaining an ideal concentration of FC that could prevent the risk of contamination within the wash system is still a technical challenge in the industry, indicating the need to better understand wash water chemistry dynamics. Using bench‐scale experiments and modeling approaches, we developed a comprehensive mathematical model to predict the FC concentration during fresh‐cut produce wash processes for different lettuce types (romaine, iceberg, green leaf, and red leaf), carrots, and green cabbage as well as Escherichia coli O157:H7 cross‐contamination during fresh‐cut iceberg lettuce washing. Fresh‐cut produce exudates, as measured by chemical oxygen demand (COD) levels, appear to be the primary source of consumption of FC in wash water, with an apparent reaction rate ranging from 4.74×10−4 to 7.42×10−4 L/mg·min for all produce types tested, at stable pH levels (6.5 to 7.0) in the wash water. COD levels increased over time as more produce was washed and the lettuce type impacted the rate of increase in organic load. The model parameters from our experimental data were compared to those obtained from a pilot‐plant scale study for lettuce, and similar reaction rate constant (5.38 × 10-4 L/mg·min) was noted, supporting our hypothesis that rise in COD is the main cause of consumption of FC levels in the wash water. We also identified that the bacterial transfer mechanism described by our model is robust relative to experimental scale and pathogen levels in the wash water. Finally, we proposed functions that quantify an upper bound on pathogen levels in the water and on cross‐contaminated lettuce, indicating the maximum potential of water‐mediated cross‐contamination. Our model results could help indicate the limits of FC control to prevent cross‐contamination during lettuce washing.

Chlorine inactivation ofEscherichia coli O157:H7in fresh produce wash process: effectiveness and modeling

“…The advantage of this model is that measuring each of these organic reactants involves complicated analytic methods while measuring COD is relatively quick and straightforward. Moreover, we and other researchers have reported the strong correlation between produce-water ratio and COD levels for various types of produce (Abnavi, Alradaan, Munther, Kothapalli, & Srinivasan, 2019;Li et al, 2019). Therefore, with careful calibration of commercial systems, it is possible that the measurement of COD is redundant.…”

A Wash of Ethyl Acetoacetate Reduces Externally Added Salmonella enterica on Tomatoes

“…This is similar to our log reductions for S. Newport MDD14 and S. Typhimurium FSL R6-0020. Problems with chlorine washes for produce include the consumption of free chlorine that is necessary to reduce bacterial numbers by fresh-cut produce exudates [ 27 ] and the production of stronger biofilm by the bacteria upon chlorine stress via induction of the oxidative stress response [ 28 ]. In tomatoes, it has been shown that field debris and defective tomatoes at less than 1% make up for 55.5% of the chlorine demand in the wash [ 29 ].…”

Microbes in Our Food, an Ongoing Problem with New Solutions

“…On leafy greens, chlorine as well as range of other chemicals are used in the wash water to reduce cross-contamination [15]. Intriguingly, the efficacy of such treatments can be limited because of the inactivation of the free chlorine by fresh cut plant exudates, which facilitates cross-contamination during the wash cycles [16]. In addition, bacteria can form biofilms on many surfaces, including stainless steel, when treated with sub-lethal concentrations of the anti-microbial [17].…”