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Title

INACTIVATION OF MURINE NOROVIRUS AND MS2 COLIPHAGE DURING FREEZE-DRY DEHYDRATION OF CONTAMINATED STRAWBERRIES

Creator

Wang, Xueyan

Date

2013, 2013-07

Description

Human norovirus (HuNoV) is the major causative agent of foodborne acute gastroenteritis in the US and worldwide. A 2012 norovirus outbreak...
Show moreHuman norovirus (HuNoV) is the major causative agent of foodborne acute gastroenteritis in the US and worldwide. A 2012 norovirus outbreak that was associated with frozen strawberries has led to more than 11,000 illnesses in Germany. Freezedrying, a common process used to preserve berries, has been questioned for its effectiveness of norovirus inactivation. In our study, the survival of MS2 coliphage and murine norovirus-1 (MNV-1), surrogates of HuNoV, on inoculated strawberries were evaluated during a 24hr freeze-dry dehydration process with and without radiant heat. Fresh strawberries were 7 mm-thickness sliced, virus-inoculated, 1hr frozen, and 24hr freeze-dried. Freeze-drying of inoculated berries with the temperature ranging from 0 to 40°C was studied with continuous recording of the temperatures once every 20 min. Infectious MNV-1 was quantified using a Raw 264.7 cell culture plaque assay. The quantification of MS2 was conducted using a double agar plaque assay. The average recovery of MS2 coliphage from berry slices by an elution protocol developed in the study was 97% ± 27% based on the inoculum as 100%. Only 57% ± 11% of MNV was recovered from berry slices using the identical elution protocol. Approximately half of the recoverable population (either MS2 or MNV-1) became undetectable after 24hr cold storage, the final average recovery being 46% and 29% for MS2 and MNV-1 respectively. Radiant heat was found to accelerate the reduction of MS2 up to 2.56 logs reduction per sample in the process. The overall reduction of MS2 was about 3 logs as maximum after 24hr freeze-drying. Regression analysis illustrated a significant correlation between MS2 log reduction and radiant heat applied. The x regression formula suggested that an increase of one degree Celsius in radiant heat during the 24hr freeze-drying would increase the log reduction of MS2 on berries by 0.044 log. The reductions of MNV on berries after the 24hr freeze-drying ranged from 0.85 to 1.82 logs. Via ANOVA analysis, MNV reduction on berries with radiant heat ≥20°C was significantly greater than heating at 10°C or without heat (~0°C), p<0.05. The overall maximum reduction of MNV on berries after the 24hr-process, therefore, was >2 logs. Although radiant heat inactivated MNV during the freeze-drying process, the inactivation of MNV by heat was less efficient than that of MS2. These data may be helpful in designing processes to control viral contaminants during freeze-drying of virus-contaminated berries.
M.S. in Food Safety and Technology, July 2013
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