# Efficacy of Chlorine, QAC, and UV-C Light Against Listeria monocytogenes Biofilms on Food Contact Surfaces

## TL;DR

This study tests how well chlorine, QAC, and UV-C light remove Listeria biofilms from food contact surfaces, finding that surface type and biofilm age affect their effectiveness.

## Contribution

The study provides new insights into how surface material and biofilm age influence sanitizer efficacy in produce-processing environments.

## Key findings

- Chlorine, QAC, and UV-C light were less effective against older L. monocytogenes biofilms.
- Stainless steel surfaces showed higher log reductions compared to PET and silicone rubber.
- Organic matter from apple juice reduced the effectiveness of all sanitizers.

## Abstract

Listeria monocytogenes biofilms on surfaces that come into contact with food create ongoing challenges in produce-processing environments, highlighting the necessity for effective surface sanitation. This research examined the effectiveness of chlorine (200 ppm), quaternary ammonium compound (QAC, 400 ppm), and UV-C light (0.85 J/cm2) against L. monocytogenes biofilms developed on stainless steel, polyethylene terephthalate (PET), and silicone rubber materials frequently used in apple packing settings. Biofilms were cultivated using a mixture of LCDC and V7 strains in diluted apple juice and evaluated after 1 and 7 days of growth. The type of surface material and the age of the biofilm had a significant impact on the performance of the sanitizing agents (p < 0.05). Chlorine achieved a reduction of 2.84 ± 0.06 log CFU/coupon on 1-day-old biofilms on stainless steel, although its effectiveness dropped to 1.90 ± 0.07 log CFU/coupon on biofilms aged 7 days. Similar trends were noted for QAC (2.42 ± 0.05 to 1.73 ± 0.06 log CFU/coupon) and UV-C (2.71 ± 0.05 to 1.57 ± 0.08 log CFU/coupon) over time. PET and silicone rubber consistently exhibited lower log reductions than stainless steel for all treatments. The presence of organic matter from apple juice reduced the efficacy of sanitizers on all surfaces. These results emphasize the significant role of surface material, biofilm age, and organic load on sanitation effectiveness, offering practical recommendations for enhancing the control of L. monocytogenes in produce-processing facilities.