Enhanced steam-sanitizer strategies for eliminating Listeria biofilms on food-contact surfaces

Food processing equipment contaminated with Listeria monocytogenes is a major cause of listeriosis outbreaks implicated in various fresh produce, highlighting the need for effective surface sanitization strategies to eliminate this pathogen from food-contact surfaces. This study evaluated the effectiveness of steam treatments at temperatures ranging from 100 to 142 °C, with or without chemical sanitizers, against Listeria innocua (a surrogate for L. monocytogenes) biofilms on stainless steel (SS), polyester (PET), and rubber surfaces. Seven-day-old L. innocua biofilms on these surfaces were subjected to short-time steam treatments at 100, 125, and 142 °C, either alone or in combination with 10 ppm peroxyacetic acid (PAA) or quaternary ammonium compound (QAC). Culturable L. innocua cells were then detached and enumerated. Results showed that steam treatments exhibited quick killing efficacy during the come-up time (CUT, 8–12 s), regardless of steam temperatures or surface materials. For example, steam CUT at 100–142 °C led to reductions of culturable L. innocua by 3.0–4.2 log₁₀ CFU/coupon on SS, 2.5–2.9 log₁₀ CFU/coupon on PET, and 2.4–2.8 log₁₀ CFU/coupon on rubber, respectively. However, killing rates decreased beyond the CUT and with extended steam exposure, showing more pronounced survival tails on PET and rubber compared to SS. To enhance the eradication of L. innocua biofilms, PAA or QAC at 10 ppm was applied for 1 min, followed by a short (CUT + 6 s) steam treatment at 125 °C, which resulted in ≥4.9 log₁₀ CFU/coupon reductions of culturable L. innocua on all surfaces. Rubber surfaces showed the greatest resistance to these hurdle treatments compared to SS and PET. The findings from this study provide effective surface sanitization strategies for the food industry to control L. monocytogenes in processing facilities.