Sanitation and Design of Lettuce Coring Knives for Minimizing Escherichia coliO157:H7 Contamination

This study was undertaken to examine the effect of ultrasound in combination with chlorine on the reduction of Escherichia coliO157:H7 populations on lettuce coring knives. Two new coring devices designed to mitigate pathogen attachment were fabricated and evaluated. The coring rings of the knives were dip inoculated with soil slurry containing 106E. colicells and treated with chlorinated water with and without ultrasonication for 30, 60, and 120 s. The rough welding joints on currently used in-field lettuce coring knives provided a site conducive to bacterial attachment and resistant to cell removal during sanitation treatment. The two modified coring knives harbored significantly fewer E. colicells than did the currently used commercial model, and the efficacy of the disinfection treatment was high (P< 0.05). Ultrasound treatment reduced the E. coliO157:H7 counts to below the detection limit of 1.10 log CFU/cm2at both the coring ring blade and welding joint within 30 s in 1 ppm of chlorinated water. The redesigned coring knives and an ultrasound plus chlorine combination treatment may provide practical options for minimizing the microbial safety hazards of lettuce processed by core-in-field operations.