Reduction of Listeria on stainless steel surfaces is impacted by sanitizer application method

Pathogen cross-contamination during food production is controlled through sanitation. However, sanitizer efficacy is often studied in bench-scale experiments (e.g., submerged coupons in static or stirred sanitizer) which poorly approximate fluid dynamics. This limits our understanding of how effective sanitization is in commercial application. This study paired computational fluid dynamic (CFD) estimates of shear stress during spray application of sanitizer with measurements of Listeria innocua reduction on stainless steel by 100 ppm hypochlorite sanitizer under various application methods. Static submersion of inoculated coupons for 3 s resulted in a log reduction of 2.3 {+/-} 0.1 log CFU. Bench-scale spray application for 3 s had the largest microbial reduction at the point of sanitizer spray impingement (7.5 {+/-} 0.5 log CFU) and directly adjacent to the impingement point (6.4 {+/-} 0.7 log CFU) where shear stress was the highest. Surface locations below the impingement point that only received fluid film sanitizer run-off had a significantly lower microbial reduction of 0.4 {+/-} 0.1 log CFU (p < 0.05). At the pilot scale, sanitizer spray manually applied by operators achieved a 2.5 {+/-} 0.4 log CFU reduction, which was significantly lower than what was achieved during bench-scale spray application (p < 0.05). Microbial reduction from manual operation of spray equipment was also significantly different among operators (p < 0.05). Discrepancies between bench-scale spraying, pilot-scale spraying, and submerged coupons underscores the need for sanitizer validation under realistic conditions to better understand the risk reduction achieved through sanitation programs during food processing.