Two Generally Recognized as Safe Surfactants plus Acidulants Inactivate Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in Suspension or on Dip-Inoculated Grape Tomatoes

Abstract

Contamination of fresh produce with the foodborne pathogens Salmonella enterica, Listeria monocytogenes, and Escherichia coli O157:H7 continues to be problematic, resulting in outbreaks of foodborne illness and costly corporate recalls. Various individual concentrations of citric or lactic acids (0.35 to 0.61%) or isopropyl citrate (0.16 to 0.54%) combined with two generally recognized as safe surfactants, 0.025% sodium-2-ethyl-hexyl sulfate and 0.025% sodium dodecylbenzene-sulfonate, were tested against these three pathogens in suspension and when inoculated and dried on the surface of grape tomatoes. The efficacy of sodium hypochlorite (NaClO; at 46 ppm) was also evaluated under dirty and clean conditions in suspension after addition of 0.3 or 0.03% bovine serum albumin, respectively, as an organic load. NaClO (46 ppm) inactivated the three pathogens in suspension by <0.76 log CFU/mL after 5 min in the presence of 0.3% bovine serum albumin, whereas 9 and 15 ppm of free chlorine inactivated the pathogens by 0.64 and 2.77 log CFU/mL, respectively, after 5 min under clean conditions. Isopropyl citrate (0.16% acidulant) plus 0.05% total concentration of the two surfactants inactivated the pathogens in suspension by up to 7.0 log CFU/mL within 2 min. When applied to grape tomatoes for 2 min, 0.54% isopropyl citrate plus 0.025% concentrations of each of the two surfactants reduced Salmonella, E. coli O157:H7, and L. monocytogenes by as much as ca. 5.47, 4.89, and 4.19 log CFU/g, respectively. These reductions were significantly greater than those achieved with 49 ppm of free chlorine. Citric acid and lactic acid plus surfactant washes achieved greater inactivation than water-only washes, reducing Salmonella, E. coli O157:H7, and L. monocytogenes on tomatoes by up to 4.90, 4.37, and 3.98 log CFU/g, respectively. These results suggest that these combinations of acidulants and surfactants may be an effective tool for preventing cross-contamination during the washing of grape tomatoes, for reducing pathogens on the fruit itself, and as an alternative to chlorine for washing fresh produce.