Evaluation of the efficacy of a mixer of hydrogen peroxide and peroxyacetic acid to mitigate microbial cross-contamination of Salmonella Typhimurium and the surrogate Enterococcus faecium during triple-washing of butternut squash

Abstract

This study evaluated the effectiveness of triple washing with a hydrogen peroxide (H2O2)-peroxyacetic acid (PAA) mixer to mitigate microbial cross-contamination of Salmonella Typhimurium and the surrogate bacteria Enterococcus faecium on butternut squash. To produce cross-contamination, one or two butternut squash were dip-inoculated with nalidixic acid-resistant S. Typhimurium (4.03 log10MPN/g) or E. faecium (4.20 log10MPN/g) and then mixed with 6 (“1:6”) or 5 (“2:5”) uninoculated fresh clean squash followed by triple washing for 45 s in water, water, and then the H2O2-PAA mixer at doses 0, 0.0064, 0.25, 0.50, and 0.84 ml/dL. The most-probable-number was used to determine microbial population. Triple-washing squash with 0.25–0.84 ml/dL H2O2-PAA mixer resulted in greater (P < 0.05) reductions of S. Typhimurium and E. faecium by 2.50–3.10 and 2.01 to 3.43 log10MPN/g, respectively, than the 0 and 0.0064 ml/dL treated samples. Applying 0.25–0.84 ml/dL H2O2-PAA mixer resulted 1.02 to 1.31 and 0.84 to 1.12 log10MPN/g cross-contaminated S. Typhimurium cell counts in the “1:6” and “2:5” ratio tests, respectively. E. faecium showed similar reduced cell counts and cross-contaminated cell counts in most tested treatments compared to S. Typhimurium, indicating it is an appropriate surrogate bacterium for Salmonella during post-harvest produce washing challenge studies.