Comparison of aqueous commercial cleaners for effectiveness in removing Escherichia coli O157:H7 and Salmonella muenchen from the surface of apples

Unpasteurized fruit juice and cider have been implicated in outbreaks of Escherichia coli O157:H7 and Salmonella infections, yet various processes used to clean and sanitize fruits before producing juice have not been thoroughly studied for their effectiveness in removing pathogens. The objective of this study was to evaluate cleaners used in the apple industry for their efficacy in removing E. coli O157:H7 and Salmonella from the surface of apples. E. coli O157:H7 was transformed with green fluorescent protein plasmid (pGFP). In addition to encoding for the production of GFP, the plasmid also encodes for ampicillin resistance. S. muenchen was adapted to grow in media containing 50 microgram/ml nalidixic acid. The use of ampicillin and nalidixic acid resistant strains enabled enumeration of the pathogen without interference by microflora naturally present on apples. Unwaxed Red Delicious cv. apples were surface inoculated with 8.58 log10 cfu of E. coli O157:H7 and 8.11 log10 cfu of S. muenchen. Five commercial apple cleaners were applied at concentrations and exposure times recommended by manufacturers. Populations of E. coli O157:H7, S. muenchen, aerobic mesophiles, and yeasts and molds on apples treated with cleaners and water (control) were determined. Compared to washing with water, treatment with cleaners removed or killed up to 2.86, 3.11, 2.48, and 0.73 log10 cfu of E. coli O157:H7, S. muenchen, aerobic mesophiles, and yeasts and molds per apple, respectively. There were differences in the effectiveness of cleaners in removing pathogens, but pH (2.0 and 12.0) and concentration (1% and 5%) of cleaner, and time of exposure (0.5-2 min) were not correlated with magnitude of reduction in population. The use of some types of cleaners commercially formulated for apples may contribute significantly in attaining target 5-log10 reductions of pathogens on the fruit intended for unpasteurized juice production or the fresh produce market.