Inactivation of Murine Norovirus (MNV-1) on Strawberries by Pulsed Light (PL)

Introduction: Multiple foodborne illness outbreaks associated with strawberries have raised safety concerns about berries and berry products in recent years. Human norovirus was the leading causative agent in fresh produce outbreaks. Pulsed light (PL) is an emerging non-thermal technology for rapid inactivation of microorganisms on food surfaces, equipment and food packaging materials.

Purpose: The objective of this study was to investigate the inactivation of murine norovirus (MNV-1), a surrogate for human norovirus, on strawberries using PL.

Methods: Fresh strawberries were spot-inoculated with MNV-1 to a level of approximately 10⁵ PFU/g on the surface and treated with PL using Xenon Steripulse XL-3000TM system. Samples were exposed to PL at a rate of 3 to 100 pulses/s for up to 120 s, and the distances between quartz window and the treatment spots were from 8.3 to 13.3 cm. After treatment, viruses were extracted and recovered from the samples and quantified by viral plaque assay.

Results: The initial inoculum level was 4.8 ± 0.3 log PFU/g of sample. PL treatment was effective inactivating MNV-1 on strawberries. For different duration from 30 to 120 s, various levels of reductions were achieved. For example, at the distance of 10.8 cm, PL treatment for 30, 60, 90 and 120 s resulted in 1.4 ± 0.3, 1.5 ± 0.1, 2.4 ± 0.4 and 3.3 ± 0.4 log PFU/g reductions on strawberries, respectively.

Significance: The present study demonstrated that PL treatment was an effective intervention method to inactivate virus on strawberries and could be applied to improve the microbial safety of fresh strawberries.