Effect of sequential 405 nm blue light and mild heat treatment on Staphylococcus aureus sterilization and properties in milk

Milk is rich in nutrients but highly susceptible to contamination by Staphylococcus aureus , thus posing a threat to human health. This study investigated the effects of 40 W/m 2 405 nm blue light, both independently and with mild thermal treatment, on Staphylococcus aureus in milk, as well as the underlying sterilization mechanisms and impacts on milk quality. The results showed that exposure to 40 W/m 2 405 nm blue light for 60 minutes reduced Staphylococcus aureus in milk by 2.3 lg CFU/mL. Complete inactivation was achieved either through 10 minutes at 80 °C or 30 minutes of blue light followed by 10 minutes at 75 °C. The sequential light-thermal treatment synergistically damaged bacterial membranes, with thermal treatment exerting a more pronounced impact than light treatment. Furthermore, no viable but non-culturable (VBNC) cells were detected after the sequential light-thermal treatment, and biofilm formation was significantly inhibited. Compared to thermal sterilization at 80 °C for 10 minutes, the sequential light-thermal treatment (30 minutes of blue light followed by 75 °C heating for 10 minutes) induced lesser or equivalent changes in milk quality parameters (including pH value, apparent viscosity, riboflavin content, lipid oxidation level, aroma, and the contents of protein, fat and lactose), with the only exception being color difference. This experiment provides a novel reference for milk sterilization techniques and offers a theoretical basis for dairy enterprises in optimizing milk sterilization conditions. • 405 nm blue light (40 W/m 2 ) reduced S. aureus by 2.3 lg CFU/mL in milk after 60 min. • S. aureus was completely inactivated by 30-min blue light and 10-min 75°C heating. • The combined light-heat method was more effective than either method alone. • The combined treatment preserved milk quality as well as or better than heating.