Survival of Salmonella Typhimurium on soybean sprouts after treatment with gaseous chlorine dioxide and biocontrol Pseudomonas bacteria

Authors: RODRIGUEZ, ARMARYNETTE - University Of Puerto Rico; Olanya, Modesto; Annous, Bassam; Cassidy, Jennifer; ORELLANA, LYNETTE - University Of Puerto Rico; Niemira, Brendan

Submitted to: Food Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2016
Publication Date: 4/30/2017
Citation: Rodriguez, A., Olanya, O.M., Annous, B.A., Cassidy, J.M., Orellana, L., Niemira, B.A. 2017. Survival of Salmonella Typhimurium on soybean sprouts after treatment with gaseous chlorine dioxide and biocontrol Pseudomonas bacteria. Food Science and Biotechnology. 26:513-520.

Interpretive Summary: Outbreaks of Salmonella enterica serovar Typhimurium on sprouts and minimally processed, ready-to-eat vegetables and fruits is a perennial food and consumer safety problem. Therefore, control of S. Typhimurium on produce at post-harvest is crucial. We evaluated the effects of gaseous chlorine dioxide (ClO2)and biocontrol (non-plant pathogens) Pseudomonas chlororaphis (Pc) and P. fluorescens (Pf) on the survival of S. Typhimurium on soybean sprouts. Sprouts were dip-inoculated with S. TYphimurium prior to the application of P. chlororaphis (Pc) or P. flurorescens (Pf), and were stored 24 h at 5 deg C. The sprouts were treated with 0.4 mg/L gaseous ClO2 for 1 h (90% R.H., 13 deg C). S. enterica was enumerated on XLT-4 medium (37 deg C) and Pseudomonas strains were quantified on PAF Agar (26 deg C). The reduction of S. enterica on soybean sprouts by the two biocontrol microbes were similar and less than 1 log CFU/g of sprouts. Inactivation of S. Typhimurium by gaseous chlorine dioxide varied with storage time (0 to 168h) subsequent to treatment as pathogen populations were reduced by 2.55 to 5.35 log CFU/g of sprouts. For S. Typhimurium co-inoculated with Pseudomonas strains, pathogen reductions by gaseous ClO2 ranged were similar to the above. This suggests that combined treatments of gaseous chlorine dioxide and biocontrol bacteria can enhance the safety of soybean sprouts at post-harvest.

Technical Abstract: Control of Salmonella Typhimurium on sprouts and minimally processed produce is crucial for food and consumer safety. The aim of this research was to assess natural microflora populations on soybean and evaluate the effects of gaseous chlorine dioxide (ClO2) and biocontrol Pseudomonas on the survival of S. Typhimurium on soybean sprouts. Aerobic mesophilic bacteria, lactic acid bacteria, yeast and molds, and Pseudomonas sp. were enumerated on seeds using total plate count agar (TPC), de Man, Rogosa, and Sharpe agar (MRS), potato dextrose agar (PDA), and Pseudomonas Agar F (PAF), respectively. Soybean sprouts were dip-inoculated with S. Typhimurium prior to the application of biocontrol microbes (P. chlororaphis and P. fluorescens). After inoculation with S. Typhimurium, sprouts were treated with ClO2 at 0.4 mg/L for 1 h (90% R.H., 13 deg C). For pathogen and biocontrol recovery, Pseudomonas strains and Salmonella were assessed on PAF and XLT-4 media, respectively. Natural microflora populations (aerobic mesophilic bacteria, lactic acid bacteria, Pseudomonas sp., yeasts and molds) were low and ranged from 0.93-2.91 log CFU/g of soybean seed. Pseudomonas strains reduced Salmonella by less than 1 log CFU/g of sprouts. The reduction of S. Typhimurium on soybean sprouts by ClO2 ranged from 2.55-5.35 log CFU/g. Gaseous ClO2 treatment reduced S. Typhimurium by 3.90 (0 h), 4.47 (24 h), and 3.61 log CFU/g (168 h). When S. Typhimurium was co-inoculated with Pc or Pf, pathogen reductions on sprouts were similar. Treatments of soybean sprouts with ClO2 and biocontrol Pseudomonas can enhance the safety of soybean sprouts at post-harvest.