Masters Theses

Date of Award

5-2017

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Doris H. D'Souza

Committee Members

Mark T. Morgan, Melissa Kennedy

Abstract

Human noroviruses (HNoVs) and Aichi virus (AiV) causes significant number of gastrointestinal diseases worldwide. Tulane virus (TV), a cultivable HNoV surrogate, is used to determine control measures against HNoV. The objectives of this study were to determine the heat inactivation kinetics of TV and AiV in cell-culture media and TV in spinach using the first-order and Weibull models. TV and AiV in cell-culture media at ~7 log PFU/ml in 2-ml glass vials were heated at 50-58°C [degree Celsius] up to 10 min in a circulating water-bath. Surviving infectious viruses were enumerated by standard plaque assays using confluent host cells in 6-well plates. The Weibull model showed Td=1 [thermal decimal reduction time] values of 2.53±0.08, 1.99±0.10, 0.57±0.64 and 0.22±0.25 min, respectively at the same temperatures with z-value of 6.99°C for cell culture media in 2-ml glass vials. D-values for TV in spinach in vacuum bags were 7.94±0.09, 4.09±0.04 and 1.43±0.07min and a z-value 10.74±0.01°C by the first-order model and 4.89±0.02, 3.21±0.45 and 0.25±0.38 min for the Weibull model at 50, 54 and 58°C, respectively. TV may not be as suitable a surrogate as MNV-1 (with D50°C of 36.28 min in cell-culture media and 14.57 min in spinach in 2-ml vials) for HNoV heat inactivation studies in cell culture media in 2-ml glass vials or spinach in vacuum bags owing to its lower D and z-values. D-values for AiV in 2-ml glass vials at 50, 54, and 58°C from the first-order model were 47.62±1.2, 7.14±1.13 and 2.12±0.04 min, respectively, with a z-value of 5.92°C, while the Weibull model showed Td=1 values of 34.53±0.03, 2.59±0.05 and 0.91±0.06 min for the same temperatures, respectively. Thus, both TV and AiV have lower heat resistance than hepatitis A virus (D56°C of 8.4 min in buffer in 2-ml glass vials and 8.43 min in spinach in vacuum bags). This study helped in understanding the heat-inactivation kinetics of AiV and TV that provide data for use in thermal processing to ensure food safety.

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