UNREVEALING THE ANTIMICROBIAL BLUE LED LIGHT CAPACITY FOR E. COLI AND L. MONOCYTOGENES INACTIVATION

Antimicrobial Blue Light (aBL) has been recently discovered as a non-thermic method for sanitizing food-related environments. This technology is based on the combined action of Blue Light (400-480 nm), oxygen, and endogenous or exogenous Photosensitizers (PS). These factors lead to the formation of Reactive Oxygen Species (ROS), which are responsible for microbial death. aBL efficacy has been elucidated against several microbial pathogens and its microbial inactivation capacity depends on Light Dose (D), wavelength, and microbial species. Thus, this study aimed to exploit the antimicrobial activity of Blue LED Lights at 405, 420 and 450 nm, against E. coli and L. monocytogenes, exploiting endogenous PS. The analysis was divided into two parts. Firstly, the microbial inactivation was assessed directly on agar plates; and secondly, tests were done on a liquid substate. The direct assessment of cells in agar plates evidenced that a D > 300 J cm-2 was able to inactivate the tested microbes (ca. -6.00/-7.00 log CFU/mL) at all the wavelengths in 60 min, with only the exception of E. coli at 450 nm. Decreasing the D, results were different based on the tested microbes and the wavelength used. For the assessment on liquid media, a D < 300 J cm-2 showed different behaviour of E. coli and L. monocytogenes at the three wavelengths in 120 min. During the experiments, temperature was monitored every 30 min. The results of this research highlighted that aBL is a powerful technology for microbial inactivation in food-related environments; however, the inactivation efficiency depends on the wavelength, the microbes, and the light D.