Comparing the Efficacy of Two Triple-Wash Procedures With Sodium Hypochlorite, a Lactic–Citric Acid Blend, and a Mix of Peroxyacetic Acid and Hydrogen Peroxide to Inactivate Salmonella, Listeria monocytogenes, and Surrogate Enterococcus faecium on Cucumbers and Tomatoes

Abstract

This study was designed to evaluate two triple-wash procedures with commercial antimicrobials to inactivate foodborne pathogens and surrogate bacteria on cucumbers and tomatoes. Fresh, West Virginia, locally-grown cucumbers and tomatoes were dip-inoculated with Salmonella Typhimurium and Tennessee, Listeria monocytogenes (3-strain), and Enterococcus faecium. Produce were washed through two triple-wash steps (10 s each) including water dip, antimicrobial dip, and water dip (WAW), or water dip, water dip, and antimicrobial dip (WWA), followed by draining (2 min) on aluminum foil. A triple water (WWW) process was also included as a water only control. Tested treatments were 1) water; 2) sodium hypochlorite (SH, 100 ppm, pH-8.2); 3) acidified sodium hypochlorite (ASH, 100 ppm, pH-6.8 adjusted by citric acid); 4) lactic and citric acid blend (LCA, 2.5%); and 5) a H2O2-peroxyacetic-acid mix (SaniDate-5.0, SD-0.0064, 0.25 and 0.50%). Surviving bacteria were recovered on XLT-4 (Salmonella), MOX (L. monocytogenes), and bile esculin agar (E. faecium). Data (2 replicates/4 samples/replicate) were analyzed using the Mixed Model Procedure of SAS (P=0.05). Counts of Salmonella, L. monocytogenes, and E. faecium on unwashed cucumbers and tomatoes were 5.42 to 6.23, 6.31 to 6.92, and 6.05 log CFU/produce, respectively. Triple-wash with water only reduced all three tested bacteria by 0.45 to 1.36 log CFU/fruit. Triple-wash by WWA with antimicrobials achieved additional reductions (LsMeans) of 0.38 log CFU/cucumber (Salmonella), 0.56 log CFU/cucumber (E. faecium), 1.48 log CFU/tomato (Salmonella), 1.09 log CFU/tomato (L. monocytogenes), and 0.71 log CFU/tomato more than the WAW procedure. Applying SD-0.25% and SD-0.50% solutions in triple-washing cucumbers and tomatoes resulted in reductions (P > 0.05) similar to ASH and greater (P 0.05) in comparison with Salmonella in most cases, except for tomatoes treated with WWA. Results of this study indicate that SD could be used as an alternative antimicrobial agent for chlorine water in triple-wash processing at local small produce plants. Future pilot plant validation studies and cost-effectiveness analyses are needed for applying SD solutions in triple-wash by WV local small produce growers.

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