UV-C processing of bovine milk: Dosage requirements for 5-log bacterial reductions and impact on the bioactive proteins

Thermal treatments are typically applied to milk to ensure microbial safety but can cause degradation of some bioactive proteins. Ultraviolet-C (UV-C) irradiation is an alternative treatment that can increase microbial safety and may better preserve some bioactive proteins. However, the effect of UV-C doses validated to provide ≥5-log reduction of bacteria in bovine milk on the preservation of bioactive milk proteins remains unknown. We determined the UV-C dose (fluence) required for ≥5-log inactivation of vegetative bacteria ( E. coli O157: H7, Listeria monocytogenes , Salmonella Typhimurium and Staphylococcus aureus ) and bacterial spores ( Bacillus cereus , Bacillus subtilis ) inoculated into raw bovine milk. We compared the retention of bioactive proteins (lactoferrin (Lf), immunoglobulin (Ig) G, IgM, IgA) after exposure to UV-C doses required for ≥5-log inactivation of vegetative bacteria and spores with commercially used high-temperature short-time (HTST) and ultra-high temperature (UHT) processing via ELISA. Achieving ≥5-log reductions of all four vegetative bacteria required 14 kJ/L (termed UV-1), whereas 40 kJ/L were required for ≥5-log reductions of all bacterial spores (termed UV-2). 14 kJ/L retained IgG at higher levels than HTST ( p < 0.05) and preserved Lf and IgM at similar levels to HTST ( p > 0.05), while IgA preservation was lower than HTST (50.6% vs. 62.0%; p < 0.05). 40 kJ/L resulted in improved preservation of all bioactive proteins tested compared with UHT. The findings establish that UV-C may be a promising approach for processing whole bovine milk, particularly for enhancing bioactive protein preservation after spore-reduction treatment compared with the current industry standard (UHT). • UV-C dose validated to provide >5 log reductions of vegetative and spore-forming bacteria. • Staphylococcus aureus showed higher UV-C resistance among vegetative bacteria in whole milk. • Bacterial spores required roughly 3 times more UV-C dosage than the vegetative bacteria. • IgG retention improved with UV-C over HTST, while lactoferrin and IgM remained comparable. • Spore-targeted UV-C dosage preserved all tested bioactive proteins better than UHT processing.