Effects of simultaneous and sequential irradiation with pulsed ultraviolet, visible, and near-infrared light on microbial inactivation

The bactericidal efficacy of simultaneous and sequential irradiation with ultraviolet (UV), visible (VIS), and near-infrared (NIR) light was evaluated using an intense pulsed light (IPL) device equipped with optical bandpass filters. Salmonella enterica serovar Enteritidis, Staphylococcus aureus, and Saccharomyces cerevisiae were subjected to three treatment modes: simultaneous UV + VIS + NIR, sequential UV followed by VIS + NIR [UV-(VIS + NIR)], and sequential VIS + NIR followed by UV [(VIS + NIR)-UV]. Simultaneous irradiation achieved ≥ 5 log reductions at lower energy doses than both sequential irradiation modes. Between sequential treatments, (VIS + NIR)-UV exhibited faster microbial reduction than UV-(VIS + NIR), highlighting the importance of irradiation sequence. Notably, (VIS + NIR)-UV induced a photoreactivation mechanism that increased the S. aureus population. These results demonstrate that both spectral composition and timing of exposure significantly affect microbial susceptibility to IPL. The findings provide new insights into optimizing wavelength integration and sequencing strategies for effective nonthermal microbial inactivation in food safety applications.