Persistence of foodborne viruses on various frozen berries initially frozen at different temperatures and stored for up to two years

Transmission of foodborne viruses such as human norovirus (HuNoV) and hepatitis A virus (HAV) via frozen berries has become a significant public health concern. In this study, we investigated the long-term persistence of murine norovirus-1 (MNV-1, a HuNoV surrogate) and HAV on five types of berries initially frozen at −20, −80 or −196 °C and stored at –20 °C for up to 24 months. MNV-1 titers decreased by up to 3.2 log after 24 months, particularly on strawberries initially frozen at −196 °C, whereas HAV was more stable, with the highest reduction of 1.7 log observed under the same conditions. Viral persistence was influenced by berry type, initial freezing temperature, and storage duration. The greatest reductions were consistently observed on strawberries, possibly due to increased dehydration and recrystallization over time. Freezing at −196 °C often caused freeze-cracking of the berries, which became more frequent as frozen storage progressed, accelerating long-term dehydration and structural damage. Additionally, subsequent ice crystal growth and recrystallization likely enhanced dehydration, further reducing viral infectivity. Despite gradual reductions in titer, sufficient viral inactivation was not achieved. This reaffirms that freezing alone is not an adequate viral inactivation strategy, serving primarily as a preservation method that stabilizes food while temporarily suppressing microbial activity, rather than an effective means of eliminating pathogenic viruses. Additional interventions such as physicochemical or non-thermal disinfection are essential to ensure adequate reduction of viral infectious titer in frozen berries.