Inactivated Effect and Mechanisms of Ultraviolet-C Light-Emitting Diode on Alicyclobacillus acidoterrestris

Ultraviolet-C light-emitting diode (UVC-LED) is a new non-thermal sterilization technology. In this study, the inactivation effect of UVC-LED on A. acidoterrestris, a common juice spoilage bacterium, was investigated and the underlying mechanism was explored by measuring intracellular nucleic acid and protein leakage, membrane permeability, intracellular reactive oxygen (ROS) accumulation, and intracellular protein and DNA damage. The results showed that increasing the irradiation dose of UVC-LED enhanced its inactivation effect on A. acidoterrestris, and when the irradiation dose was increased to 50 mJ/cm², the number of viable cells in normal saline decreased by 4.6 (lg(CFU/mL)). By modeling of survival curves, it was observed that the inactivation effect of UVC-LED on A. acidoterrestris in normal saline was fitted to both the log-linear and Weibull models. The bacterium in different growth stages had different sensitivities to UVC-LED, in the logarithmic phase being more sensitive to UVC-LED. The irradiation treatment led to change in the membrane permeability and leakage of intracellular contents, indicating cell membrane damage, while intracellular ROS levels were not increased significantly (P > 0.05). Raman spectroscopic analysis and fluorescence microscopic analysis with acridine orange (AO) staining showed that the structures of intracellular proteins and DNA were changed. Overall, it was concluded that UVC-LED could inactivate A. acidoterrestris by causing DNA damage, structural change of intracellular proteins and the impairment of cell membrane permeability. According to the different degrees of damage, DNA damage may be the major reason for cell death.