Inactivation of Staphylococcus aureus in milk and milk foam by pulsed UV-light treatment and surface response modeling

Pulsed UV-light is a novel technology that can be used for effective inactivation of pathogens. In this study, efficacy of pulsed UV-light (100 to 1100 nm) was investigated for the inactivation of Staphylococcus aureus (ATCC 25923) in milk and milk foam, due to its pathogenic effect in milk and milk products. Static cell suspensions of 12, 30, or 48 mL in milk were treated under pulsed UV-light for 30, 105, or 180 s at various distances (8, 10.5, and 13 cm for milk, and 5, 8, and 11 cm for milk foam). Reductions varied from 0.16 to 8.55 log ₁₀ CFU/mL, demonstrating the ability of pulsed UV-light to inactivate S. aureus. Complete inactivation was obtained at: (1) 8 cm sample distance from the quartz window of the UV-light source, 30 mL sample volume, and 180 s time combination; and (2) 10.5 cm sample distance, 12 mL sample volume, and 180 s treatment time combination. Reductions up to 6.61 ±0.11 log ₁₀ CFU/g were obtained in milk foam for various treatment conditions. It was noted that there was a significant increase in the milk temperature (up to 90°C in some cases) during pulsed UV-light treatment, which might have also provided synergistic effect on microbial inactivation.