Electron-Beam Inactivation of a Norovirus Surrogate in Fresh Produce and Model Systems

Abstract

Norovirus remains the leading cause of foodborne illness, but there is no effective intervention to eliminate viral contaminants in fresh produce. Murine norovirus 1 (MNV-1) was inoculated in either 100 ml of liquid or 100 g of food. The inactivation of MNV-1 by electron-beam (e-beam), or high-energy electrons, at varying doses was measured in model systems (phosphate-buffered saline [PBS], Dulbecco's modified Eagle's medium [DMEM]) or from fresh foods (shredded cabbage, diced strawberries). E-beam was applied at a current of 1.5 mA, with doses of 0, 2, 4, 6, 8, 10, and 12 kGy. The surviving viral titer was determined by plaque assays in RAW 264.7 cells. In PBS and DMEM, e-beam at 0 and 2 kGy provided less than a 1-log reduction of virus. At doses of 4, 6, 8, 10, and 12 kGy, viral inactivation in PBS ranged from 2.37 to 6.40 log, while in DMEM inactivation ranged from 1.40 to 3.59 log. Irradiation of inoculated cabbage showed up to a 1-log reduction at 4 kGy, and less than a 3-log reduction at 12 kGy. On strawberries, less than a 1-log reduction occurred at doses up to 6 kGy, with a maximum reduction of 2.21 log at 12 kGy. These results suggest that a food matrix might provide increased survival for viruses. In foods, noroviruses are difficult to inactivate because of the protective effect of the food matrix, their small sizes, and their highly stable viral capsid.

Quantifying the Reduction in Potential Health Risks by Determining the Sensitivity of Poliovirus Type 1 Chat Strain and Rotavirus SA-11 to Electron Beam Irradiation of Iceberg Lettuce and Spinach

“…There is a linear relationship between dose and level of virus inactivation. This linear relationship between virus inactivation and ionizing radiation has been reported earlier (2,26,35). Poliovirus exhibited greater resistance to E-beam irradiation than did rotavirus (Table 1).…”

“…There were, however, no statistically significant differences between the D 10 values of either virus on spinach and the D 10 values of that virus on lettuce. There are other reports in the literature which suggest that the matrix in which the organisms are present influences the reduction kinetics (1,2,22,35,39). Researchers have recently reported that the human norovirus surrogate, murine norovirus, showed differential reduction when exposed to E-beam irradiation depending on whether the virus was present on cabbage or strawberries (35).…”

“…There are other reports in the literature which suggest that the matrix in which the organisms are present influences the reduction kinetics (1,2,22,35,39). Researchers have recently reported that the human norovirus surrogate, murine norovirus, showed differential reduction when exposed to E-beam irradiation depending on whether the virus was present on cabbage or strawberries (35). The differential reduction of enteric viruses (though not statistically significantly different) on different fresh produce commodities highlights the importance of choosing an appropriate treatment dose to achieve the desired reduction.…”

Susceptibility of Murine Norovirus and Hepatitis A Virus to Electron Beam Irradiation in Oysters and Quantifying the Reduction in Potential Infection Risks

“…The location of the enteric viruses within the oyster's tissue could have an influence on their sensitivity to ionizing radiation if it is protected from the reactive oxygen species. It has been reported that MNV shows differential inactivation depending on whether it is present on cabbage or strawberries (32). However, using poliovirus and rotavirus, we have recently shown that while there are inactivation differences on fresh produce, such as lettuce and spinach, these observed differences were not statistically significant (23).…”

Response to the Questions Posed by the Food Safety and Inspection Service, the Centers for Disease Control and Prevention, the National Marine Fisheries Service, and the Defense Health Agency, Veterinary Services Activity Regarding Control Strategies for Reducing Foodborne Norovirus Infections†

“…Several studies have been done with irradiation and UV radiation for inactivation of viruses; results indicate that their utility is limited (77,201,212). Although these interventions cannot completely eliminate the risk of norovirus, infection risks may be reduced.…”