Mist spraying vs. immersion of riboflavin for blue light-mediated photodynamic inactivation of Escherichia coli O157:H7.

This study compared the antimicrobial efficacy and food quality effects of riboflavin combined with 405 nm blue light (RB + BL) applied via mist and immersion approaches against E. coli O157:H7 on stainless steel (SUS) surfaces and sliced ham. On bacteria-inoculated SUS surfaces, the mist RB + BL treatment achieved 4.39 log CFU/cm2 reduction at 20 J/cm2 and reduced microbial counts to below the detection limit at 40 J/cm2, whereas the immersion RB + BL treatment reached only 3.45 log CFU/cm2 reduction even at 40 J/cm2. Based on D3d values, defined as the light dose required to achieve a 3-log reduction, the mist treatment achieved equivalent antimicrobial efficacy with approximately 2.6-fold lower light dose than the immersion treatment. Mechanistic analyses showed that the mist RB + BL treatment increased intracellular ROS levels by approximately 1.4-fold compared with the immersion RB + BL treatment and was associated with membrane damage and the leakage of nucleic acid-related intracellular components. These findings suggest that the mist system induced greater ROS-mediated oxidative stress, which may have contributed to enhanced microbial inactivation. When applied to sliced ham, the mist RB + BL treatment preserved food quality attributes, including color, water holding capacity, texture, and lipid oxidation, without significant differences from the untreated control. These findings demonstrate that the mist-based RB + BL PDI system is a promising non-thermal surface decontamination strategy that achieves superior antimicrobial efficacy at reduced energy input while maintaining the quality of solid food products.