Antifungal effect and mechanism of 405 nm light-emitting diodes combined with riboflavin on Penicillium digitatum and Penicillium italicum

AIMS: This study was designed to evaluate the antifungal effect of a 405 nm light-emitting diode (LED) combined with an exogenous photosensitizer against Penicillium digitatum and Penicillium italicum and elucidate the antifungal mechanism. METHODS AND RESULTS: The results showed that riboflavin significantly enhanced the antifungal effect of 405 nm LED illumination among the three photosensitizers tested (chlorogenic acid, chlorophyllin, and riboflavin). Riboflavin inactivated mold spores below the detection limit (∼6.0 log reduction) at a lower dose (1.9-2.6 kJ cm-2) compared to the others and LED alone. Mycelial growth and sporulation were completely suppressed by LED illumination with or without riboflavin. Adding ascorbic acid required a similar dose (3.9 kJ cm-2) for spore inactivation, suggesting reactive oxygen species (ROS) generation as the primary mechanism. Transmission electron microscopy revealed intracellular organelle damage without morphological changes in spores. Lipid peroxidation, indicated by a 6- to 8-fold increase in malondialdehyde concentration, likely caused the organelle damage. CONCLUSIONS: This study confirmed that riboflavin-mediated 405 nm LED illumination was more effective in controlling both molds than LED illumination alone, and that its antifungal effect might be due to the ROS generated by the photoinactivation of riboflavin during LED illumination, which oxidizes the membranes of intracellular organelles.