P2-36 Reduction of Escherichia coli as a Surrogate for Salmonella spp. on the Surface of Grapefruit during Various Packing Line Processes

Thursday, 30 March 2017
Michelle D. Danyluk, University of Florida, Lake Alfred, FL
Loretta Friedrich, University of Florida, Lake Alfred, FL
Jiuxu Zhang, University of Florida, Fort Pierce, FL
Mark Ritenour, University of Florida, Fort Pierce, FL
Introduction:  The US Produce Safety Rule allows for use of water that does not meet its microbial standards if corrective measures, including commercial washing to remove microorganisms, are employed.

Purpose:  This research was initiated to determine the suitability of nonpathogenic Escherichia coli as a surrogate for Salmonella spp. during citrus washing and to evaluate the removal of E.coli from grapefruit on two pilot packing lines.

Methods: The equators of whole grapefruits were inoculated, with either E. coli or Salmonella spp. and, then, dried. Treatments including fruit wetting (water, 200ppm free chlorine), fruit washing (water, 85ppm peracetic acid (PAA)), PAA with an acidic detergent, an alkaline detergent (AD), and an AD with 2% sodium-o-phenylphenate (SOPP) were applied using a lab scale brush wash system. Individual processes evaluated on the pilot packinglines with E. colionly included fruit wetting, brush washing, pre-wax drying, and wax application plus drying. with ADs, sanitizers (chlorine, PAA, SOPP), and waxes (shellac, carnauba+morpholine) were evaluated. Treated fruit were rubbed, by hand, with Dey/Engley neutralizing broth, which was enumerated on selective and non-selective media.

Results: Log reductions for E.coli populations ranged from 2.7 to 4.9, and Salmonella spp. reductions ranged from 2.8 to 4.9. In all lab scale, brush wash systems treatments, bacterial population reductions between E.coli and Salmonella spp. were not significantly different (P≤0.05). On pilot packing lines, E. coli populations were reduced by various fruit wetting, washing, waxing, drying. The complete packing line processing treatments reduced Salmonella spp. by 2.1 to >4.5 log CFU/grapefruit at one packing line system, and by 3.2 to >5.0 log CFU/grapefruit at the other. Treatment of fruit through complete packing line processing, at both locations, reduced E. coli populations to levels below the detection limit (<1 log CFU/grapefruit).

Significance:  Escherichia coli is an appropriate surrogate for Salmonella spp., under the tested conditions; citrus packers can use commercial washing as a corrective measure, if low microbial quality water was used.