Influence of Retail Crisping on Cross-contamination of Romaine Lettuce

Introduction: Contamination of fresh fruits and vegetables can occur during any processing or handling step from the farm to the table. Many retailers implement crisping, a rehydration process in which fresh produce is soaked in cool or warm water and then placed in a cooler to drain excessive water. Cross-contamination of product can occur during crisping the result of contaminated equipment, product, and workers.  

Purpose: Crisping of lettuce was conducted with and without a sanitizer to determine control of E. coli O157:H7 in crisping water and prevention of cross-contamination.

Methods: Romaine lettuce (2 heads) were inoculated with E. coli O157:H7 and were soaked with six non-inoculated heads in 21°C water for 5 min. Treatment included potable tap water and tap water containing 30 ppm chlorine. The lettuce heads were removed and processed for microbiological analysis. Water samples were obtained immediately prior to and after treatment for determining pH and for microbiological analysis.  The experiment was competed three times.

Results: E. coli O157:H7 was not detected following crisping in water containing 30 ppm chlorine.  Based on enrichment of lettuce samples cross-contamination occurred in water alone and water plus 30 ppm chlorine. Reductions of 2 and 1.5 log CFU of E. coli O157:H7 and commensal flora, respectively, occurred on inoculated lettuce treated with 30 ppm chlorine.

Significance: Cross-contamination can occur during crisping.  A reduction in pathogenic and native flora on inoculated lettuce can be achieved when a sanitizer is used. Including a sanitizer in the crisping water will control the level of foodborne pathogens and commensal/spoilage bacteria in the water. Addition of a sanitizer to water used for crisping is recommended and may improve product shelf life and reduce human health concerns.