Standardizing Produce Wash Water Models for Validation of Postharvest Sanitizers

Introduction: The CDC reports over 45% of foodborne illnesses are produce related, making development of methods to reduce these outbreaks imperative.  Adding sanitizing agents at adequate levels to the postharvest washing process has been shown to reduce contamination. Current research has used a variety of model wash water models to validate the efficacy of sanitizers, however, this makes comparing historical research challenging for manufacturers to select appropriate produce sanitizers for their operation. Therefore, development of a standardized model is critical to produce recommendations.  

Purpose: Previous research has evaluated factors including Chemical Oxygen Demand and turbidity, however, there is little consistency between approaches. The purpose of this project is to understand what the common characteristics of industrial postharvest wash water are and identify appropriate measurable attributes to create a model system.

Methods: In this study, two types of were profiled: 1) water samples at the end of a postharvest washing 2) lab prepared produce purees diluted to 25 and 50 NTU and autoclaved before being treated with 50 ppm chlorine.   Samples were analyzed for free residual chlorine using HACH kit, Total Organic Carbon (TOC), and Oxidation Reduction Potential (ORP).

Results: ORP, TOC, and turbidity results did not indicate correlation in free residual chlorine.  For example doubling turbidity caused a change in free chlorine of 0.66 ppm, 1.17 ppm, and 4.00 ppm for the cucumber, yellow squash and red pepper, respectively.  The ORP value changes were 90.57 mV, 70.30 mV, and 10.64 mV for the cucumber, yellow squash and red pepper, respectively.  The same change in turbidity resulted in a change of TOC of 62.34 mg/l in our cucumber model. 

Significance: It is imperative that a standard model be used to make comparisons between different sanitizers to help stakeholders implement best agricultural safety practices. This data suggests that individual models will have to be developed for quantifying sanitizer effectiveness.