Purpose: To evaluate the variables that affect virus survival in HPP treatment of contaminated strawberry mash.
Methods: Fresh strawberries were blended, degassed, inoculated with the virus surrogate MS2 coliphage (6-9 log PFU) and packed (1 ml) into a transfer pipet that was placed into a secondary bag to contain potential leaks. Using HPP pilot system Avure QFP 24L-828-S, inoculated strawberries were processed at constant temperature (14 to 40°C) and pressure (300 to 600 MPa) with 3-min holding time. To achieve constant temperature during the process while pressure increased, pre-tests were performed to appropriately adjust the initial process temperature (-3 to 21ºC). A polyethylene cylindrical container enclosing all samples was used to maintain the holding temperature, which was monitored throughout the entire process. Viruses in matrices were quantified by plaque assay.
Results: MS2 in acidic berry mash and neutral tryptic soy broth (TSB) decreased by 0.43 and 3.2 logs, respectively, after 600 MPa treatment with 20°C holding temp. When berry samples were inoculated with 10% and 15% of MS2/TSB, the higher ratio of berry samples (90% berries with 10% inoculum) improved the MS2 survival by 2-fold (at 400 MPa x 20°C). Therefore, greater survival of MS2 was observed in the solid matrix compared to liquid regardless of pH. The MS2 inactivation in berry mash was more effective with higher pressures, but still less than 1 log inactivation was observed after 600 MPa x 20°C process. As the holding temperature increased, the MS2 survival generally decreased. However, ≤10% difference in the survival was shown in berries between 20°C and 40°C x 600 MPa processes.
Significance: The information is valuable for determining virus survival during HPP treatment of contaminated fruits.