Validation of triple-wash procedure with a H2O2-peroxyacetic acid mixer to improve microbial safety and quality of butternut squashes and economic feasibility analysis

This study aims to i) evaluate two triple-wash procedures with an H2O2-peroxyacetic-acid mixer (SaniDate-5.0) to improve microbial safety and quality of butternut squashes and ii) determine the feasibility of the triple-wash application in a processing plant. In study I, fresh squashes were dip-inoculated with a mixture of Salmonella and Listeria monocytogenes, followed by two triple-wash steps including water dip-antimicrobial dip-water dip (WAW) or water dip-water dip-antimicrobial dip (WWA). Tested antimicrobials were i) lactic/citric acid blend (LCA; 2.5%); ii) sodium hypochlorite (SH; 100 ppm); and iii) SaniDate-5.0, 0.0064, 0.25 and 0.50%. Surviving bacteria were recovered using XLT-4 agar for Salmonella and MOX agar for L. monocytogenes. In study II, freshly harvested squashes were either left unwashed or triple-washed using WWA in water and SaniDate-5.0 (0.0071 and 0.45%) at a processing plant followed by storage at 9 °C for 70 days. Aerobic Plate Counts (APCs), coliforms/Escherichia coli, lactic-acid-bacteria, and psychrotrophs on squashes were tested every seven days. Counts of Salmonella and L. monocytogenes on unwashed squash were 5.0–5.3 and 5.4–6.0 log CFU/squash, respectively. WWA wash was more effective (P < 0.05) in reducing Salmonella (2.5 log CFU/squash) and L. monocytogenes (2.3 log CFU/squash) than WAW (1.8 log CFU/squash for Salmonella and 0.3 log CFU/squash for L. monocytogenes). Antimicrobials caused different degrees in reduction of Salmonella (1.7–2.6 log CFU/squash) and L. monocytogenes (1.2–1.8 log CFU/squash) on squashes, while the highest was achieved with SantiDate-5.0 (0.25 or 0.5%). During storage, SaniDate-5.0 treated squashes showed lower (P < 0.05) counts of APCs, coliforms, lactic-acid-bacteria, and psychrotrophs than the unwashed and water-treated samples on days 50–70. The estimated annual operating cost of the triple-wash process with SaniDate-5.0 ranges from $487.05 to $1977.33 for growers producing 1000–5000 squashes. The WWA procedure with SaniDate-5.0 appears to be an economically feasible way for local small producers to improve microbial safety and quality of squashes during postharvest processing.