The reduction of murine norovirus 1, B. fragilis HSP40 infecting phage B40-8 and E. coli after a mild thermal pasteurization process of raspberry puree.

Pasteurization processes of raspberry puree are nowadays limited to short times and rather low temperatures to maintain flavor and nutritional quality. Norovirus (NoV) outbreaks associated with raspberries highlight the need to determine the survival of NoV on this type of soft fruit. Therefore, resistance of murine norovirus 1 (MNV-1), a surrogate for human NoV, B. fragilis HSP40 infecting phage B40-8, and E. coli towards mild pasteurization was tested. Raspberry puree heat treated at 65 degrees C for 30s showed a 1.86, 2.77, and 3.89 log reduction of, respectively, MNV-1, E. coli, and B40-8. Heating at 75 degrees C for 15s established a 2.81 log reduction of MNV-1 while a 3.44 and 3.61 log reduction of B40-8 and E. coli was observed. No supplementary lethal effect of holding the heat-treated raspberry puree at 4 degrees C overnight was noticed. B40-8 failed to be useful as a tool to monitor NoV inactivation during mild pasteurization processes. Moreover, <3 log reductions of MNV-1 were observed suggesting that upon high initial contamination load, infectious NoV particles may remain on mildly pasteurized raspberry puree.