Efficacy of Chlorinated Nanobubble Solutions to Control Shiga Toxin-producing Escherichia coli, Salmonella spp., and Non-pathogenic Escherichia coli Surrogates in Chilled Solutions

Introduction: Antimicrobial interventions are effective to reduce pathogen risks on processed produce, meat, and poultry products. Chlorinated solutions have been widely studied in produce and poultry wash waters, but have not been evaluated with inclusion of nanobubble technology. Interest in nanobubble technology has increased due to its proposed surfactant properties; however, it is undetermined whether this technology aids in effectiveness of chlorine-based solutions in food applications.

Purpose:  Benchtop studies were conducted to evaluate the efficacy of chlorinated nanobubble waters against Shiga toxin-producing Escherichia coli O26, O45, O103, O111, O121, O145, and O157:H7 (STEC-7), Salmonella spp., and USDA-approved non-pathogenic STEC surrogates in pure culture to characterize the lethality contributions of pH (5 or 7), temperature (1.6 or 5.6°C), free available chlorine (FAC) level, inclusion of nanobubbles, or a combination thereof.

Methods:  Chlorinated waters (0 to 11.94±0.97 ppm FAC) were manufactured with and without inclusion of nanobubbles, and with and without CO₂ gas addition to adjust pH. Pure culture cocktails of STEC-7, Salmonella spp., and surrogates were added to chlorinated water treatments for 60 seconds, subsequently neutralized, and surviving population levels quantified.

Results:  Surrogate organisms demonstrated greater resistance (P ≤ 0.05) across all combinations of chlorinated solution treatments (3.4-5.5 log CFU/mL reductions) than pathogens tested; thus, proving to be an appropriate surrogate for STEC and Salmonella for commercial in-plant studies. Higher reductions (P ≤ 0.05) were observed across all target organisms at high (11.94±0.97 ppm) FAC levels. STEC-7 and Salmonellapopulation reductions were also notably reduced (3.3-7.1 log CFU/mL) by the chlorinated nanobubble waters. No definitive impacts of temperature, nanobubble inclusion, or acidic pH were observed in pure solutions.

Significance: Determining the impact of nanobubble inclusion in chlorinated solutions will allow for increased knowledge of the technology and its contributions to food safety applications.