Impact

• The integrated multi-disciplinary approaches taken by the project engineers, microbiologists, and food scientists uncovered myths behind the penetration of sanitizer through a layer of exudate, and developed new visualization techniques and a state-of-the-art image processing algorithm to delineate and quantify the outcome of drop impacts on produce surfaces.

  • Information gained from this project enables fresh-cut processors to improve food safety by systematic rather than trial-and-error approaches.

• The project team also invented a novel fresh-cut washing system that improves the washing process efficacy and filed a nonprovisional patent application. 

• Our team’s research with four multi-state retail grocery chains is showing significant improvements in control and compliance with food code temperatures during display of fresh-cut produce in refrigerated cases, with the added benefit of major conservation of energy.  

• Our project website developed to provide easy access to project activities and workshop trainings on water sanitation practices to industry personnel, and accomplishments for stakeholders. 

Output

Objectives 1 & 2: 

The project team comprehensively evaluated the major sources of chemical oxygen demand, and chlorine demand in wash water of diced cabbages.

• We characterized the types/contents of sugars, phenolic compounds, organic acids, proteins and peptides in the produce wash water, but chiefly, their roles in depleting free chlorine. Diced cabbage is known to present major challenges to maintaining required free chlorine levels during commercial washing. Delineation of these important chemical classes and their abundance in wash water fills critical data gaps on produce food safety, and paves the road for safe and effective wash water treatments.   

• We conducted microbial community analyses on spinach and the environment in a commercial fresh-cut processing facility using DNA sequencing to determine the effects of sanitizer and storage conditions on changes in the natural resident bacterial populations. Results can inform processors about potential contamination routes, thereby improve product/environmental sanitation.

• We developed a method based on dual-wavelength ultraviolet light absorbance (UVA) to predict real-time chlorine demand during produce washing.  Using cut cabbage, carrot, lettuce, and onion as model food products, we showed that UVA changes relative to the amount of organic material in the water and the residual chlorine demand. This method forms a basis for development of an automated chlorine control replenishment system in continuous commercial produce washing processes.

In collaboration with an industry partner, the first research unit of a single pass wash system was fabricated and installed in our pilot plant. On-going research studies focus on improving the washing efficacy of the single-pass system by optimizing water nozzle types and configurations in collaboration with two leading nozzle manufacturers. 

Objective 3:

• We fabricated and tested our novel produce wash system for cleaning fresh-cut produce immediately after cutting, and submitted a nonprovisional patent application. As produce falls downward, a spray manifold directs fluid upward to spray and impact the tumbling produce, thereby thoroughly coating/cleaning it.

• Computations of the capacity to wash away a soluble contaminant, such as plant tissue exudate or residual chlorine, from a rough produce surface, will provide major insight into the flow velocities and thicknesses required. Using a computational fluid dynamics approach, we have nearly completed analyses of “wash-away” scenarios for characteristic 2-D roughness elements. 

  • These are the first detailed convective mass transfer computations performed for any nontrivial flow in any geometry at a Schmidt number over 10.

  • Results suggest that different flow regimes (e.g. spray) would effectively wash away a contaminant and potentially reduce contact time and wash water requirements. 

• Further computations will include characteristic 3-D roughness elements and 3-D topographies from actual produce surfaces. 

  • We also measured the viscosity of aqueous solutions over a range of temperatures to use in our computations; these are the first such data for any six-carbon sugar acid.

• We are currently working on computations for the penetration of sanitizer through a layer of exudate, including the reaction of sanitizer with exudate to understand the importance of removing exudate before the application of hypochlorite.

  • When complete, these computations will inform decisions about "washing before sanitization”

• We are also conducting research on fresh produce to examine impact dynamics of spray drop shape on particulate matter removal, sanitizer deposition, and rinsing.

• Our team established the scientific basis for fundamentally new approaches to improve the process of spray washing of produce and sanitizer deposition.

  • We developed new visualization techniques, and a state-of-the-art image processing algorithm to delineate/quantify the outcome of drop impact on produce surfaces and the role of the drop speed, size, and fluid properties when coupled with surface roughness of produce.

    • These findings revealed key factors in fluid retention on surfaces after impact from spray drops.

• Our ongoing work focuses on mixing during spray impact on dry, rough, and pre-wetted surfaces.

  • The fundamentally novel mathematical models and physics we developed can be used to improve produce washing, sanitizing, and rinsing to optimize pathogen control.

Objective 4:

• Our research with four different multi-state retail chains involves continuous data collection (180 temperature/relative humidity sensors in refrigerated display cases) in 10 grocery stores. Data has helped our industry partners deal with key issues with retrofitting doors on display cases.

• We also identified potential air flow and contamination collection points during temperature monitoring in various case locations. Our team recommended changes to best practices for temperature control in closed display case settings and showed that implementing these changes can result in 90% reduction in warm temperature abuse. We worked with store- and chain-level management to improve maintenance and improve safety and consumer experience.

Objective 5:

• The project team has been very active and productive in outreach and disseminating information to our major stakeholders, including the fresh and fresh-cut produce industry, retail industry, food safety regulatory agencies, and the international scientific community.

  • Our means of communication include social media, our website, YouTube videos, site visits, face-to-face meetings, consulting, video conference calls, emails, and meeting presentations, as well as peer-reviewed journal publications. 

• Within the first two weeks of project approval, we held our first project team and stakeholder advisory board (SAB) meetings in conjunction with the industry’s public policy conference held in Washington, D.C.

  • The team interacted with SAB members and laid out solid plans for collaboration, fulfillment of milestones, and measurement of success. 

  • We held four additional quarterly conference calls with the SAB and shared our findings with the industry. 

• To reach out to the fresh-cut produce industry, project team personnel organized a fresh-cut workshop at UC Davis attended by more than 60 industry participants. The PD and two Co-PIs of our project shared our project findings with the attendees. 

• We also shared project findings during an industry food safety council meeting attended by more than 70 industry technical executives.

• We further contributed to industry sponsored "white papers" widely distributed throughout the entire produce industry.

• In addition, we co-organized a working group involving members of USDA and FDA, and other food safety researchers, on topics at the interface between mathematical modeling and empirical data, and provided technical consultations to numerous fresh produce companies, as well as site tours.

• Another important stakeholder group that we have reached out to is the retail industry, where temperature control is important to food safety, but challenging to maintain.  Through collaborative research and on-site testing, our team worked with seven retail chains throughout the United States. 

• Our research also interacted broadly with the international scientific community concerning produce food safety, time and temperature control for food safety, and fluid dynamics of produce washing.

  • We disseminated findings through scientific publications and presentations in the US and international platforms, as well as classroom technical and hands-on lab practices.

  • We educated and trained many undergraduate and graduate students and post-doctoral research associates.

  • One unique aspect of our project is the focus on fluid dynamics and produce sanitization.

  • Currently, there is essentially no awareness in the fluid dynamics community of the importance of produce safety (or more generally, food safety), and our talks at the annual meeting of the American Physical Society Division of Fluid Dynamics helps to fill the void. 

  • In addition, we presented symposium talks and seminars internationally, including in France, Greece, Singapore, and China.

• We also include our research in the development of new curricula to train students. 

  • At the University of Illinois, we included some discussion of produce washing in a foundational fluid mechanics course, exposing 17 engineering graduate students (from four graduate curricula) to the issues and importance of this application, with which none was previously familiar.

  • At MIT, we developed a curriculum, and are training students on disease transmission, sprays, and surface science.

  • At the USDA-ARS, we offered tours to more than 30 undergraduate students from the University of Maryland, and mentored five post-doctoral research associates on food safety research. 

• We developed and launched a new website (https://www.producefoodsafety.org/) featuring the project activities, publications, poster presentations, and videos.  This website features the latest results of the research portion of the proposal along with national news related to fresh and fresh-cut produce.