Exploring Blue Light Inactivation of Foodborne Viruses on Strawberries During Washing

Human norovirus (HuNoV) and hepatitis A virus (HAV) are the main enteric viruses causing foodborne viral outbreaks. Frozen berries have been implicated in multi-state and international outbreaks attributed to these viruses. Because strawberries undergo washing immediately prior to freezing, supplementary non-thermal interventions are needed during this step to enhance viral inactivation. The objective of this study was to explore the use of blue light (405 nm) inactivation of foodborne viruses on strawberries during washing. Because infectious HuNoV is difficult to generate in cell culture, Tulane virus (TV) was used as a surrogate. Strawberries were contaminated with TV or HAV then submerged in sterile water under gentle shaking, with or without BL treatment (~1000 J/cm²) at room temperature. A modified FDA/BAM/26 method was used to recover infectious viruses, and the infectivity titers were quantified using the 50% tissue culture infectious dose (TCID₅₀) assay. Indigenous bacteria on strawberries and in the wash water and the water physiochemical parameters were monitored. The combined effect of washing strawberries under blue light (~1000 J/cm²) resulted in ~1.7 and 1.5 log reduction for TV and HAV on strawberries and 1 log reduction in wash water, respectively. Bacteria count on washed strawberries or in wash water were not impacted by BL. Blue light significantly increased the oxidizing potential of the wash water while not impacting the pH, turbidity, or temperature of the water. In conclusion, this study demonstrates that BL treatment during strawberry washing can reduce the viral load on strawberries and in wash water. Further optimizations will be critical to adapt this technology to enhance strawberry safety, quality and prevent cross-contamination during the washing process.