Viruses are the leading cause of foodborne illness worldwide (67%). Specifically, human norovirus (HuNoV) is the major foodborne virus. Fresh produce is often at high risk for norovirus contamination because it can be easily contaminated at both pre-harvest and post-harvest stages and it undergoes minimal or no processing. There is an urgent need to develop novel interventions to eliminate foodborne enteric viruses in fresh produce. High pressure processing (HPP), a non-thermal processing technology may provide a new approach to reduce the virus load in fresh produce and related products. In the present study, we systematically investigated the effectiveness of HPP on inactivating norovirus in aqueous medium, lettuce, strawberry, and fruit puree using murine norovirus (MNV-1) as a surrogate for noncultivable HuNoV. Approximately 5 log virus reduction was observed in all food items upon treatment at 400 MPa for 2 min at 4°C, demonstrating that HPP is effective in reducing the MNV-1 load in fresh produce. Moreover, our results showed that pressure, pH, temperature, and the food matrix affected the virus survival. MNV-1 was more effectively inactivated at 4°C than at 20°C. MNV-1 was also found to be more sensitive to high pressure at neutral conditions (pH 7.0) than at acidic conditions (pH 4.0). Taken together, these findings support the notion that HPP is a promising intervention to eliminate the norovirus risk in fresh produce and related products while the organoleptic and nutritional properties of these foods are affected to the minimal extent.
To further evaluate the potential of HPP in inactivating viruses, we continued to investigate the effectiveness of HPP on the inactivation of human rotavirus (HRV), vesicular stomatitis virus (VSV), and avian metapneumovirus (aMPV). HRV represents a major foodborne virus other than HuNoV and is non-enveloped; VSV and aMPV are enveloped and their virion structures are strikingly different from those of MNV-1, HuNoV, and HRV. We found that HPP was capable of efficiently inactivating all tested viruses at optimal conditions, although the pressure susceptibilities varied considerably among these viruses. Under the pressure of 350 MPa at 4°C for 2 min, 1.1-log, 3.9-log, and 5.0-log virus reductions were achieved for VSV, HRV, and aMPV, respectively. Additionally, both VSV and aMPV were more susceptible to HPP at higher temperature and lower pH. In contrast, HRV was more easily inactivated at higher pH and inactivation appeared to be independent of temperature. These results suggest that the presence of an envelope, temperature, and pH contribute to the susceptibility to HPP independently for each virus.
We also explored the mechanisms underlying HPP-induced inactivation using MNV-1, HRV, and VSV as models. We found that the damage to the virion structure by disrupting the viral envelope and/or the viral capsid, not the degradation of viral genomic RNA, was the primary mechanism of HPP-induced inactivation of all these viruses. Notably, even when the virion structures were completely damaged upon HPP, the major immunogenic proteins (such as MNV-1 capsid protein and VSV glycoprotein) remained antigenic, implying that HPP-inactivated viruses could be used as candidate for inactivated vaccines.