Variable fluid mechanics explain why static efficacy tests overestimate sanitizer performance against Listeria

Area of Science:

• Food safety
• Microbiology
• Chemical engineering

Background:

• Environmental sanitation is key to controlling pathogen cross-contamination in food production.
• Traditional sanitizer efficacy studies often use bench-scale methods that don't mimic real-world fluid dynamics.

Purpose of the Study:

• To investigate the impact of fluid dynamics and shear stress on sanitizer efficacy.
• To compare microbial reduction under different application methods: pilot-scale spray, bench-scale spray, and static submersion.

Main Methods:

• Paired computational fluid dynamics (CFD) with experimental measurements of *Listeria innocua* reduction.
• Applied 100 ppm hypochlorite sanitizer using various methods on stainless steel surfaces.
• Measured microbial reduction (log CFU/surface) at different locations and conditions.

Main Results:

• Pilot-scale manual spraying achieved 2.6 log CFU/surface reduction, with significant variation between operators.
• Bench-scale spraying showed higher reduction (up to 7.5 log CFU/surface) at high shear stress points.
• Lower reduction (0.4 log CFU/surface) occurred in low shear stress areas; static submersion yielded 2.3 log CFU/surface.

Conclusions:

• Bench-scale sanitizer tests do not accurately predict real-world efficacy due to unrepresented fluid dynamics.
• Realistic testing conditions are essential for accurate risk assessment and effective food safety policy.
• Sanitizer efficacy is significantly influenced by shear stress and fluid dynamics during application.