Purpose: The survival of HAV on strawberry slices was studied during 24 h freeze-dry process (radiant heat ≤40°C) and subsequent storage of dehydrated products at room temperature.
Methods: Fresh strawberries were sliced (7 mm-thickness), inoculated with 5 log PFU HAV/sample, air dried 20 min, frozen at -80°C for 1 h, and freeze-dried 24 h. The strawberry freeze-drying was conducted in FreeZone 12 (Labconco, Kansas City, MO) in multiple trials. HAV survival on strawberry slices was determined by plaque assay using FRhK-4 cells grown in six-well dishes.
Results: Trials averaged 60±14% and 21±9% for total recovered HAV from inoculated berries immediately after air-drying for 20 min and 24 h-cold storage, respectively. The HAV reduction on strawberries after 24 h freeze-drying (with <40°C radiant heat) was ≤0.5 log, compared to corresponding berries 24 h-cold stored as controls. HAV seemed to survive greater than previously studied murine norovirus (MNV, ≤1.8-log reduction) during berry freeze-drying, although similar recoveries of HAV and MNV from fresh and cold stored berries were observed. This freeze drying process did not cause major HAV inactivation on berries. Further investigation on HAV survival on dehydrated berries during room temperature storage will be conducted.
Significance: This research illustrates the persistent nature of HAV on contaminated berries during freeze-drying with radiant heat to 40°C. Thus, preharvest and harvest controls of fruits, intended to precede this type postharvest process, are critical for minimizing viral hazards.