UV inactivation of milk-related microorganisms with a novel electrodeless lamp apparatus

摘要

A novel UV apparatus based on Dean vortex technology is designed for inactivating bacteria in milk. In this apparatus, the milk flows through a helical quartz tube coiling around an electrodeless UV lamp (EUL) with a radio frequency of 2.65 MHz. Flow rate, inner diameter of quartz tube, different UV sources, and different types of bacteria have been found as the key factors for the valuable effects on bacterial inactivation. The EUL apparatus worked more efficiently in the UV inactivation of the predetermined populations of milk-related bacteria than the conventional low-pressure high-intensity mercury lamp. When the UV dose of 21.3 mJ/cm2 was applied, the numbers of all the bacteria were reduced by more than 6 log10 with a flow rate of 28.8 L/h and a tube’s inner diameter of 1.5 mm. Dean vortices were formed in the milk flow during the UV processing and played an important role in the UV inactivation of the bacteria. Another inactivation test with the apparatus applying the UV dose of 21.3 mJ/cm2 was also done with raw cow’s milk containing indigenous microorganisms, including Salmonella and Shigella spp., Listeria monocytogenes, Staphylococcus spp., Enterobacteriaceae, lactic acid bacteria, pseudomonads, and the total aerobic bacteria were reduced by approximately 3–4 log10. In short, the EUL apparatus requires smaller energy, occupies less space, and has simpler operating procedures than thermal pasteurization. Thus, the novel method provides a viable alternative to thermal pasteurization of milk for improving the microbial safety of milk and extending its shelf life.