Survival of Hepatitis A Virus on Two-month Stored Freeze-dried Berries.

Abstract

Imported berries have contributed to U.S. hepatitis A virus (HAV) infections. Minimal processing by freeze-drying is preferred by industry for preserving food quality, but virus inactivation by this process may be limited. This study investigated HAV survival on strawberries during 24-h freeze-drying followed by 22 ° C-storage. The outer surfaces of strawberry slices were prepared and each inoculated with 5 to 6 log 10 PFU HAV, air-dried 20 min, frozen 1 h at -80 °C, and freeze-dried 24 h with radiant heating up to 36 °C. Infectious HAV levels eluted from berry slices were quantified on FRhK-4 cells grown onto 6-well dishes. Freeze-drying trials (n = 17) with radiant heating inactivated ≤1 log 10 PFU per trial, although HAV-inactivation was significantly greater at 36 ºC than 15 ºC heating ( p < 0.01). Average HAV reduction rate on dried berries continuously decreased as storage time increased, 0.2, 0.09, 0.08, 0.04, 0.04 and 0.03 log-reduction/day at day 2, 7, 14, 28, 42, and 56, respectively, with the cumulated log-reduction divided by storage days. Therefore, the best fit regression for the total/cumulative virus reduction (Y) at any given day (X) is Y= 0.2882X 0.4503 (r² = 0.97), with maximum 2.7 log-reduction on berries throughout the drying and subsequent 2-month storage. HAV showed the greatest decline within the first 14-days of storage of dried berries (approximately 70% weekly reduction from its previous week levels), but the HAV reduction rates were still lower than that occurring on fresh produce.