Effectiveness of Ultra-High Irradiance Blue-Light-Emitting Diodes to Control Contamination Adhered to Dry Stainless Steel Surfaces.

Controlling contamination in dry food processing environments represents a significant challenge due to their tolerance to desiccation stress and enhanced thermal resistance. Blue light is emerging as a safer alternative to UV irradiation for surface decontamination. In the present study, the antimicrobial efficacy of ultra-high irradiance (UHI) blue light, generated by light-emitting diodes (LEDs) at wavelengths of 405 nm (841.6 mW/cm) and 460 nm (614.9 mW/cm), was evaluated against a five-serovar cocktail of dry cells on clean and soiled stainless steel (SS) surfaces. Inoculated coupons were subjected to blue light irradiation treatments at equivalent energy doses ranging from 221 to 1106 J/cm. Wheat flour was used as a model food soil system. To determine the bactericidal mechanisms of blue light, the intracellular concentration of reactive oxygen species (ROS) in cells and the temperature changes on SS surfaces were also measured. The treatment energy dose had a significant effect on inactivation levels. On clean SS surfaces, the reduction in counts ranged from 0.8 to 7.4 log CFU/cm, while, on soiled coupons, the inactivation levels varied from 1.2 to 4.2 log CFU/cm. Blue LED treatments triggered a significant generation of ROS within cells, as well as a substantial temperature increase in SS surfaces. However, in the presence of organic matter, the oxidative stress in cells declined significantly, and treatments with higher energy doses (>700 J/cm) were required to uphold the antimicrobial effectiveness observed on clean SS. The mechanism of the bactericidal effect of UHI blue LED treatments is likely to be a combination of photothermal and photochemical effects. These results indicate that LEDs emitting UHI blue light could represent a novel cost- and time-effective alternative for controlling microbial contamination in dry food processing environments.