Survival and inactivation of human norovirus surrogates in blueberry juice by high-pressure homogenization

Human noroviruses (HNoV) have been implicated in gastrointestinal outbreaks associated with fresh produce, juices, and ready-to-eat foods. In order to determine the risk of HNoV transmission by contaminated blueberry juice, survival characteristics of cultivable HNoV surrogates (murine norovirus, MNV-1; feline calicivirus, FCV-F9; and bacteriophage MS2) in blueberry juice (pH=2.77) after 0, 1, 2, 7, 14, and 21 days at refrigeration temperatures (4°C) were studied. High-pressure homogenization (HPH) was studied as a novel processing method for noroviral surrogate inactivation in blueberry juice. Blueberry juice or phosphate-buffered saline (PBS; pH 7.2 as control) was inoculated with each virus, stored over 21 days at 4°C or subjected to HPH, and plaque assayed. FCV-F9 (∼5 log₁₀ PFU/mL) was undetectable after 1 day in blueberry juice at 4°C. MNV-1 (∼4 log₁₀ PFU/ml) showed minimal reduction (1 log₁₀ PFU/mL) after 14 days, with greater reduction (1.95 log₁₀ PFU/mL; p<0.05) after 21 days in blueberry juice at 4°C. Bacteriophage MS2 (∼6 log₁₀ PFU/mL) showed significant reduction (1.93 log₁₀ PFU/mL; p<0.05) after 2 days and was undetectable after 7 days in blueberry juice at 4°C. FCV-F9 remained viable in PBS for up to 21 days (2.28 log₁₀ PFU/mL reduction), while MNV-1 and MS2 survived after 21 days (1.08 and 0.56 log₁₀ PFU/mL reduction, respectively). Intriguingly, FCV-F9 and bacteriophage MS2 showed reduction after minimal homogenization pressures in blueberry juice (pH=2.77), possibly due to the combination of juice pH, juice components, and mechanical effects. MNV-1 in blueberry juice was only slightly reduced at 250 (0.33 log₁₀ PFU/mL) and 300 MPa (0.71 log₁₀ PFU/mL). Virus surrogate survival in blueberry juice at 4°C correlates well with the ease of HNoV transmission via juices. HPH for viral inactivation in juices is dependent on virus type, and higher homogenization pressures may be needed for MNV-1 inactivation.