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

Abstract

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).