Virucidal activity of gamma radiation on strawberries and raspberries

The environmental stability of enteric viruses and resistance to conventional treatments and common disinfectants, leads to their persistence in waters and food, causing serious implications on public health. Among non-thermal treatment methods, ionizing radiation is recognized as a useful and effective mean of disinfection. The objective of this study was to estimate the inactivation of enteric virus by gamma radiation in raw berry fruits, in order to evaluate the potential of this technology to be applied as a disinfection treatment. Fresh strawberries and raspberries were inoculated either individually with murine norovirus type 1 (MuNoV; as a human norovirus surrogate) and human adenovirus type 5 (HAdV) or with a viral pool of both viruses, and irradiated in a Co-60 equipment at doses of 1 kGy up to 11 kGy. The infectivity of viral particles of MuNoV and HAdV was assessed by plaque assay using Raw 264.7 and A549 cells, respectively. A 2 log PFU/g reduction on MuNoV and HAdV titers was obtained after treatment with a dose of 4 kGy for both fruits. However, non-linear inactivation survival curves were obtained for MuNoV and HAdV in fresh fruits, leading to the detection of infective viral particles at a dose of 11 kGy. The irradiation process indicated virucidal potential, although the estimated gamma radiation dose to attain food safety (> 7 kGy) would compromise the preservation of food quality. Nevertheless, the irradiation technology could be an effective virus mitigation tool to treat polluted waters, which are a major vehicle of contamination for fresh produce.