Thermal pasteurization process has long been employed to provide safety of milk and other dairy products. However, heat treatment may cause substantial changes in flavor and nutritional composition, particularly induce enzyme inactivation, protein denaturation, and lipid oxidation in milk. Moreover, thermal process is also energy and cost-consuming in comparison with other disinfection methods. Therefore, it is necessary and practical to develop non-thermal methods to inactivate the pathogenic bacteria in milk.

Ultraviolet (UV) irradiation is considered a promising non-thermal alternative method, as it is lethal to most types of microorganisms. UV light irradiation could induce physical shifting of electrons and breaking bonds in deoxyribonucleic acid (DNA) as well as DNA pyrimidine bases mis-pairing in most microorganisms with greater effect at the wavelengths between 250 and 260 nm. The US Food and Drug Administration (FDA) regulations have approved the use of UV-light for fresh juices and it has been successfully commercialized in food industry. Particularly, UV is also energy-efficient and cost-effective in real practice.

Recently, a Chinese researcher -Dr. YIN Fugui from Institute of Subtropical Agriculture, Chinese Academy of Sciences and his foreign colleagues from Guelph Food Research Center, Agriculture & Agri-Food Canada conducted a study to investigate the inactivation efficacy of monochromatic UV light against pathogenic E. coli as well as to examine the potential reactivation of it at refrigerated and ambient temperatures following exposure to these three UV light sources in bovine milk.

The researchers found that the inactivation efficiency of the UV light at 254 nm was higher than that at 222 and 282 nm on E. coli O157:H7 in bovine milk. The reactivation ratio of E. coli O157:H7 following exposure to the UV light at 254 nm was lower than that at 222 and 282 nm in milk medium. Therefore, exposure to the UV light at 254 nm followed by storage at refrigerator conditions would be a practical and effective way to control the safety of milk.

This research was supported by the Risk Mitigation Program of Agriculture & Agri-Food Canada. F. Yin was a visiting graduate student financially supported by the China Scholarship Council through the MOE-AAFC Ph.D. Research Program, and is currently an NSERC Visiting Fellow to the Canadian Federal Government Laboratories (NSERC-VF).

The study entitled “Inactivation and potential reactivation of pathogenic Escherichia coli O157:H7 in bovine milk exposed to three monochromatic ultraviolet UVC lights” has been published in Food Microbiology, details could be found at http://dx.doi.org/10.1016/j.fm.2015.01.014.

YIN Yulong,

Institute of Subtropical Agriculture, Chinese Academy of Sciences

yinyulong@isa.ac.cn