Inactivation of Escherichia coli O157:H7, Salmonella enterica and murine norovirus on blueberries using a novel water-assisted ultraviolet light process
Date
2015
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Fresh produce, such as blueberries, has been associated with foodborne illnesses. The most common causative agents include Escherichia coli O157:H7, Salmonella and norovirus. Chlorinated water has been widely used by the food industry to wash fresh produce to achieve some level of microbial decontamination. However, chlorine wash can lead to the formation of carcinogenic substances. The ability of ultraviolet (UV) light to inactivate bacteria and viruses is well established; however, its application on food commodities is limited because of their shadowing effect. In the present study, a novel set-up using water-assisted UV processing was developed to inactivate Escherichia coli O157:H7, Salmonella and murine norovirus (MNV-1) on fresh blueberries. The effect of different wash water qualities was also investigated for MNV-1 inactivation. Blueberry samples were exposed to UVC light alone (dry UV) or immersed in agitated water during UV treatment (wet UV). Wet UV treatment generally showed higher efficacies than dry UV treatment for both bacteria and virus inactivation. E. coli was most easily killed on skin-inoculated blueberries, followed by calyx-inoculated berries. Wet UV treatment of 10 min resulted in 5.2- and 3.9-log reductions of E. coli for skin- and calyx-inoculation methods, respectively. Dip-inoculated blueberries were the most difficult to decontaminate and 1.6-log reduction of E. coli was achieved after 10-min wet UV treatment. With a similar result, MNV-1 was more easily killed on skin-inoculated than on calyx-inoculated blueberries. Wet UV treatment of 5 min resulted in >4.36 and 3.04-log reductions of MNV on skin- and calyx-inoculated blueberries, respectively. Wet UV treatments were comparable with a 10-ppm chlorine wash. Addition of 100-ppm sodium dodecyl sulfate (SDS), 0.5% levulinic acid or 10 ppm chlorine to washing solutions did not significantly enhance the wet UV treatment for bacteria inactivation. UV irradiation combined with 10 ppm chlorine wash was comparable to wet UV treatment alone for MNV-1 inactivation. Presence of 2% blueberry juice in wash water provided protection to MNV-1 from UV irradiation or chlorine wash treatment. Inactivation efficacy was comparable between UV+DI water wash and UV+DI water (5% blueberry crush) wash. Overall, this study shows that UV treatment could be used as an alternative to chlorine wash for blueberries and potentially for other fresh produce.