| Human norovirus is the most prevalent cause of acute non-bacterial gastroenteritis, causing an estimated 1 in 15 people to become ill each year. Fresh produce such as leafy greens are at high risk for norovirus contamination because they typically undergo little to no processing after harvest. For these fresh foods and other foods where thermal processing is not practical or consumers have decided that they prefer more fresh-like, minimally processed foods, the use of non-thermal technologies for food processing has emerged. The non-thermal technologies that we investigated in this study include electron beam irradiation (e-beam), ozone, pulsed electric field (PEF) processing, and other sanitizers and surfactants. Our results showed that Tulane virus (TV) was able to be reduced to non-detectable levels in lettuce by e-beam irradiation at 8.7 kGy or higher, and in strawberries at 16.3 kGy or higher, but these levels of irradiation are higher than currently allowed by FDA regulations (FDA, 2013). Visual changes to the food were significant at doses of 8.2 or 8.7 kGy or higher in strawberries and lettuce, respectively. We also found that the human norovirus surrogate, murine norovirus-1 (MNV-1), was more resistant to e-beam treatment than Tulane virus. It appeared that the combination of disruption of the structure, viral proteins, and RNA are all essential in viral inactivation by irradiation.;Gaseous ozone was able to significantly reduce two human norovirus surrogates' viral titer in both liquid virus stock and in strawberries and lettuce. MNV-1 was slightly more resistant to gaseous ozone. Based on SDS-PAGE, electron microscopy, and RT-PCR results, ozone was able to successfully disrupt virion structure and completely degrade viral proteins, while leaving genomic RNA intact in both viruses. Thus, the primary way ozone disrupts norovirus surrogates is by altering the capsid structure and damaging the viral capsid proteins on the surface of the virus.;We evaluated the effectiveness of chlorine, sodium dodecyl sulfate (SDS), levulinic acid, and combinations of these treatments for the removal or inactivation of Tulane virus in fresh produce and in virus stock over time. Modest concentrations of SDS in combination with chlorine was the most effective sanitizer associated with strawberries and virus removal. For lettuce, traditional chlorine solution performed the best, followed by levulinic acid in combination with chlorine. Over a 72 h period incubation with the treatments, SDS with chlorine showed the most virucidal activity, giving 4.8 logs of viral reduction. None of the other treatments tested were able to successfully degrade viral protein or viral RNA, except for SDS in combination with chlorine. Ultimately, chlorine remained the most effective antiviral treatment under our conditions.;Pulsed electric field was used to inactivate both MNV-1 and TV in liquid virus stock. We showed that using square wave 3 musec pulses, 29.5 kV, and 8.8 A conditions, that we were able to achieve 1.2 and 2.4 log reductions in MNV-1 and TV, respectively. This is the first account of significant foodborne viral reduction by PEF treatment. Each of these different non-thermal technologies all show great promise in future food safety applications. |
