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United States Department of Agriculture

Agricultural Research Service

Research Project: Innovative Technologies and Process Optimization for Food Safety Risk Reduction Associated with Fresh and Fresh-Cut Leafy Green Vegetables

Location: Environmental Microbial and Food Safety Laboratory

2013 Annual Report


1a.Objectives (from AD-416):
1. Inactivation of pathogens and prevention of cross-contamination through optimization of produce wash system design and operation; 2. Development of innovative washing processes and technologies; and 3. Prevention of pathogen proliferation in supply chain.


1b.Approach (from AD-416):
This project takes a system-based and trans-disciplinary approach to address food safety issues of leafy green vegetables. The project involves research in the fields of mechanical engineering, microbiology, post-harvest technology, and food processing. "Speciality Crop Research Initiative."


3.Progress Report:

Major progress has been made in this project, and three critical issues facing the industry have been addressed. First, we determined the minimum free chlorine concentration needed to prevent pathogen survival and transference during commercial produce wash. Second, we developed a mathematical model to characterize the dynamic relationships between free chlorine, organic load, chloramine hump, and chlorination breakpoint during simulated produce wash with increasing organic load. Third, we further examined the dynamic relationship between free chlorine concentration, organic load, and exposure time on the inactivation of 12 pathogenic strains of Salmonella, Escherichia coli O157:H7 and Non-O157 STEC. This has significantly advanced the general knowledge and understanding of the dynamic relationship between fresh-cut produce wash operations, water quality, sanitizer efficacy, and produce quality and safety. Currently, a number of fresh-cut processors are already using these results to revise the operational parameters for their wash systems to provide preventive controls against pathogen transference. We fully leveraged the team’s expertise in the fields of pre- and post-harvest technology and engineering to examine the effects of realistic contamination matrices on pathogen reduction. Spinach samples were inoculated in the USDA Beltsville’s research field and tested in both USDA and University of Illinois facilities. Sample inoculation mimicked real-life leafy green contamination scenarios with E. coli cells mixed with other possible contamination matrices including soil, compost, and dairy manure. We tested washing treatment combinations of: chlorine; chlorine and ultrasound; and chlorine, ultrasound, and surfactants. The Illinois team further validated the USDA team’s prior studies of improving food safety by reversing the traditional cut and wash sequence. The team also modified the wash system to improve submergence of whole-head lettuce during washing Produce managers in retail stores routinely perform internal audits of their equipment thermostat settings and product temperatures as determined by instant-read non-contact thermometers. ARS has determined, through this research project, that the commonly-used infrared thermometer technology is not an appropriate method for determining the product temperature of bagged leafy-greens. Data are being compiled to design, modify and implement infrared (IR) technology to achieve an accurate and 'instant read' temperature of bagged produce. Completion of IR study will greatly facilitate in-house, third-party, state and federal government inspections by providing a method to quickly and accurately determine where temperature abuse is occurring. In order to facilitate rapid dissemination of the scientitific information to the stakeholders, the team organized a Beltsville, Maryland, food safety conference with stakeholders, advisors and team members to disseminate information and obtain feedback. Approximately 15 industry members of the United Fresh Produce Association were also in attendance. Following presentations of research findings, the attendees discussed the application of the findings for developing food safety standards, and the next steps and directions of the project. The ARS researchers also provided a tour of the research facility, including their fresh-cut produce pilot plant and a mini supermarket with commercial produce display cases. In addition, project team members also shared information with the stakeholders extension meetings held in California.


Last Modified: 12/18/2014
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