Efficacy of ultraviolet (UV-C) light in reducing foodborne pathogens and model viruses in skim milk

The efficacy of low wavelength ultraviolet light (UV-C) as a disinfection process for a scattering fluid such as skim milk was investigated in this study. UV-C inactivation kinetics of two surrogate viruses (bacteriophages MS2 and T1UV) and three bacteria Escherichia coli ATCC 25922, S. Typhimurium ATCC 13311, Listeria monocytogenes ATCC 19115 in buffer and skim milk were investigated. UV-C irradiation was applied to stirred samples, using a collimated beam operating at 253.7 nm wavelength. A series of known UV-C doses (0–40 mJ·cm⁻²) were delivered to the samples except MS2 where higher doses (0–150 mJ·cm⁻²) were delivered. Biodosimetry, utilizing D values of viruses inactivated in buffer, was carried out to verify and calculate reduction equivalent dose. At the highest dose of 40 mJ·cm⁻², the three pathogenic organisms were inactivated by more than 5 log₁₀ (p <.05). Results provide evidence that UV-C irradiation effectively inactivated bacteriophage and pathogenic microbes in skim milk. The inactivation kinetics of microorganisms was well described by log linear and exponential models with a low root mean squared error and high coefficient of determination (r² > 0.96). Models were validated and parameterized for predicting log reduction as a function of UV-C irradiation dose (p <.05). This study clearly demonstrated that high levels of inactivation of pathogens can be achieved in skim milk, and suggests significant potential for UV-C treatment of treating fluids that exhibit significant scattering. Practical application: This research paper provides scientific evidence of the potential use of UV technology in inactivating pathogenic bacteria and model viruses in skim milk. UV-C doses were validated and verified using biodosimetry. UV-C irradiation is an attractive food preservation technology and offers opportunities for dairy and food processing industries to meet the growing demand from consumers for safer food products. This study clearly shows the potential for using UV-C treatment for treating highly scattering fluid such as skim milk. Results from this work will be used to further develop continuous flow-through UV-C systems based on dean or turbulent flow patterns.