Wavelength-specific UV-C inactivation kinetics of foodborne pathogens in stirred liquid suspensions and droplets on contact surfaces

This study investigates the inactivation kinetics of B. cereus ATCC 14579 (endospores) and E. coli ATCC 25922 when exposed to UV-C light at varying wavelengths (254, 265, 279, and 284 nm). Two scenarios were investigated: stirred liquid suspensions and unstirred static settings (droplets on stainless steel surfaces). The results reveal that the UV-C transmittance through microbial suspensions follows order of 284 > 279> 254 > 265 nm. In stirred conditions, the inactivation kinetics of microbial suspensions exhibited a correlation with the absorption spectra, leading to inactivation kinetic constants order: 265 > 254>279 > 284 nm. However, when focusing on comparative studies of B. cereus inactivation under unstirred conditions, a different order emerged: 265 > 279>284 > 254 nm. Notably, the overall trend revealed that inactivation kinetic constants tend to be higher in unstirred settings, apart from the 254 nm. These variations in inactivation order and kinetic constants can be attributed to enhanced protein damage at wavelengths 265, 279, and 284 nm under unstirred conditions compared to stirred. In summary, we observed effective germicidal efficiency of UV-C light at 265 nm, in both experimental conditions. However, for experimental conditions involving low light transmission through microbial structures such as biofilms, wavelengths of 279 and 284 nm holds considerable promise, ensuring efficient light penetration and enhanced inactivation efficiency.