Can clean get cleaner? Evaluation of cleaning and sanitation process improvements for harvest equipment of leafy greens

A baseline assessment conducted in 2023/24 to define “What is clean” funded by the Center for Produce Safety provided near real-time data on Cleaning & Santation (C&S) practices in states under the FDA Leafy Greens Harvester Sampling Assignment (CA, AZ, FL). Key findings included: (1) Cleaning tools and detergents impact microbial reductions more than sanitizers alone; (2) Chlorinated detergents significantly reduced ATP, Total Coliforms, and E. coli; (3) The cleaning step itself has the most significant bacterial reduction effect; (4) Cross-contamination risks exist in current SOPs; (5) ATP monitoring effectively evaluates C&S effectiveness in real time. Simple changes—such as better tools, dedicated cleaning time, proper chemical application, and improved crew training—enhanced C&S performance. However, initial study conditions likely represented a best-case scenario, as equipment was cleaned immediately after harvest. Real world conditions, including prolonged equipment sitting, may increase biofilm formation, requiring adjustments like low-pressure or foamer applications to improve efficacy.  This project will build on previous efforts to assess the impact of harvester sitting time, continuous sanitizer use, the use of two new chemistries not evaluated previously PAA and CLO2, and improved tool usage to refine industry practices and enhance harvest equipment sanitation efficacy.

In 2023/24 the research team embarked on a special study funded by the Center for Produce Safety to provide near “real time” data to industry on the status of the C&S procedures. Over to course of the study, much was learned about the variability in treatment chemistries, C&S crew size, tools used by industry to complete C&S, as well as the incidence of indicator bacteria before, during, and after a sanitation event.
Key learnings include the following: (1) Detergent type and application, as well as the tools used during cleaning, have a greater impact on microbial reductions than sanitizers alone; (2) Chlorination detergents significantly reduced ATP, Total Coliform bacteria and generic E. coli; (3) The cleaning (detergent) step itself has the most significant impact on reducing bacterial loading on harvest machines; (4) crosscontamination risks are present in current SOPs; and (5) ATP can be used effectively to evaluate C&S effectiveness in real time, aiding in immediate corrective actions if needed. However, one thing remained clear, simple changes, such as the availability of ladder/platform, dedicated brushes, verification tools, dedicated employee time, appropriate chemicals, and application methods (foamers, increased coverage, appropriate contact times), and highlighting areas of concern to cleaning crews, significantly improved C&S effectiveness. Another significant finding was that data reported in this initial study likely represented the best-case scenario, as equipment was cleaned immediately following harvest day (i.e., did not sit overnight), and in some cases firms were preparing or had recently prepared for FDA sampling assignment visit(s). One important consideration for prolonged residence time (equipment sitting) is the impact that may have on biofilm formation and adhesion to harvest machine surfaces. To combat the potential implications of enhanced biofilm formation and adhesion or organic matter and other particulates, we will work with the C&S firms to modify their sanitation applications to utilize low pressure and/or foamer applications. From our initial work in 2023/2024, our data suggested that high pressure sanitation created opportunities for increased over-spray cross contamination, and incomplete coverage. By reducing the pressure of the sanitizer application or utilizing a foamer for the detergent application, the C&S crews will increase the intended contact time of the chemical/detergent on harvest machine surfaces. By increasing the contact time and coverage, this will likely increase efficacy and ultimately log reduction of the bacterial targets analyzed for the study. As such, we propose to build on this important research effort to(Objective 1) enhance our understanding of the impact of time/temperature (prolonged equipment sitting), as well as (Objective 2) evaluate specified tool and continuous sanitizer use on the effectiveness of cleaning and sanitation of harvest machines to inform industry practice. These objectives will be achieved through ATP monitoring following two recommended industry field formats (Charm and Hygiena) as well as the use of microbiological indicators generic E.coli, Total Coliform bacteira, Aerobic Plate Count bacteria, Enterobacteriaceae and non-microbiological targets Protein and Lactose/Glucose to assess C&S efficacy in three key produce growing regions of the United States; Arizona, California, and Florida.

Objective 1: Enhance our understanding of the impact of time/temperature (prolonged equipment sitting), through aggressive sample collection and assessment in three produce growing regions of the US (AZ, CA, and FL)
Objective 2: Evaluate specified tool and continuous sanitizer use on the effectiveness of cleaning and sanitation of harvest machines to inform industry practice.