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United States Department of Agriculture

Agricultural Research Service

Research Project: Minimizing Pathogen Transference During Lettuce Harvesting by Optimizing the Design of the Harvesting Device and Operation Practices

Location: Environmental Microbial and Food Safety Laboratory

2012 Annual Report


1a.Objectives (from AD-416):
To develop techniques to improve food safety and quality of fresh and fresh-cut produce using ultra-sound and other emerging technologies; to investigate the effect of various new sanitizers on pathogen reduction and shelf-life extension of fresh-cut fruits and vegetables; and to gain a greater understanding of how fresh-cut processing conditions affect plant metabolism, microbial growth, and their interactions.


1b.Approach (from AD-416):
ARS will acquire the basic knowledge of the factors influencing pathogen transference during lettuce harvesting. The Cooperator will provide the expertise in equipment design and disinfection. Advanced molecular and microbiological techniques will be applied to quantify pathogen concentrations spanning a range of realistic contaminant loads and field conditions; creative engineering approaches will be utilized to optimize coring knife design and develop enhanced sanitation practices.


3.Progress Report:

Examination of the design of the current commercially used coring knife in relation to E. coli O157:H7 adherence and attachment revealed that the rough surface connecting the coring ring and the shaft harbors significantly more E. coli O157:H7 than the smooth surfaces and has much less disinfection efficacy. When coring knives are washed in chlorine alone, at least 50 ppm free residual chlorine was needed in the wash solution to inactivate E. coli O157:H7 on welded knife parts, whereas 10 ppm residual chlorine was needed for the smooth areas. However, combining ultrasound with chlorine significantly improved chlorine efficacy on pathogen inactivation in the rough surfaces. When ultrasound for 1 min was combined with chlorine, pathogen inactivation to undetectable levels was achieved at 1 ppm residual free chlorine on all knife parts. Adding surfactant (Tween 80) to the chlorine solution did not improve the inactivation of E. coli O157:H7 cells on the welding joint of the knife. To further address disinfection issues associated with rough welds. Two prototype coring knives were developed and tested. The prototypes included a no-joint design and a polished weld joint design. Polishing weld joints may be an option for retrofitting the currently used knives in the industry. Test results show that the two prototype knives harbored significantly fewer E. coli O157:H7 cells on the coring rings than the commercial ones and facilitated more effective E. coli O157:H7 inactivation by chlorine. Prototypes were field tested during lettuce harvest. Positive feedback was received from the industry.


Last Modified: 7/30/2014
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