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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL FOOD SAFETY OF FRESH AND FRESH-CUT PRODUCE Title: Ultrasound as an intervention technology for the sanitation of lettuce harvesting knife

Authors
item Zhou, Bin -
item Feng, Hao -
item Luo, Yaguang

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: March 13, 2010
Publication Date: July 17, 2010
Citation: Zhou, B., Feng, H., Luo, Y. 2010. Ultrasound as an intervention technology for the sanitation of lettuce harvesting knife. [abstract]. Annual Meeting of the Institute of Food Technologists.

Technical Abstract: Lettuce field-coring and trimming practices are recent industry developments designed to improve fresh-cut processing yield and reduce shipping and waste disposal costs. Studies showed that the harvesting/coring knives used could be potentially contaminated with pathogens by contact with contaminated soils and plants, thereby cross- contaminating subsequent harvested lettuce. Chlorine, while currently used to sanitize harvesting/coring knives in field, has limited efficacy on pathogen inactivation. Ultrasound has demonstrated effectiveness for sanitizing stainless steel food contact surfaces, but has not been tested for its potential to improve sanitization of lettuce harvesting/coring knives. This research examined the effect of ultrasonication and chlorine on reduction of E. coli populations on coring knives. Knives were inoculated by dipping in soil slurries containing E. coli K-12 cells for 1 minute followed by air-drying for 2.0 hours. Knives were then submerged in solutions containing 1, 10, 50, 100, or 200 ppm free chlorine, with or without ultrasonication (25 kHz, 500W/L) for 0.5, 1, or 2 min. Knife surfaces were swabbed with wetted cotton rods then enumerated for E. coli populations via a direct plating method. Results indicate that the rough welding point of the knife harbored more E. coli cells than the smooth areas. Ultrasonication treatment significantly improved the efficacy of chlorine on E. coli inactivation of the coring knives, especially at the welding point. A 30-second ultrasonication treatment (25 kHz, 500 W/L) with 1 ppm chlorine reduced E. coli to an undetectable level whereas a significant amount of E. coli cells remained when knives were treated with chlorine alone. This suggests that ultrasonication holds substantial potential for improving the sanitation of lettuce harvesting/coring equipment.

Last Modified: 4/16/2014
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