Use of pulsed ultraviolet laser light for the cold pasteurization of bovine milk

Because of concerns that some potentially dangerous microorganisms may survive conventional heat pasteurization of milk and because the heat needed to sterilize milk affects marketability, the ability to efficiently cold pasteurized milk may become more desirable. In this pilot study, we investigated the use of pulsed ultraviolet (PUV) laser light to nonthermally (cold) pasteurized bovine milk. Dairy bulk tank milk was treated with UV light (248 nm) emitted from a pulsed excimer laser. The samples were then analyzed for surviving bacteria by spiral plate counting and subculturing in Trypticase soy broth. Other bulk tank milk samples were inoculated with one of eight relevant milk bacterial species before being exposed to laser light. There was no growth observed for any of the plated or subcultured samples exposed to 25 J/cm2. One bacterial isolate was then used to inoculate milk to further investigate bactericidal laser light doses. Growth was observed for samples treated with an average of 0.3 to 6.6 J/cm2 but not for those treated with 12.6 J/cm2. The results indicate that in principle, the bacterial content of milk can be adequately controlled by exposure to PUV laser light.