Inactivation of murine norovirus on green onions and in salsa by high pressure processing, and inactivation of Salmonella on blueberries by a novel ultraviolet light and washing process
Date
2014
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Publisher
University of Delaware
Abstract
Two projects are presented in this thesis. In the first project, high pressure processing was tested as a method for inactivation of a surrogate for human norovirus (murine norovirus) in green onions and salsa. Conditions for high pressure treatment, inactivation kinetics at 300 and 350 MPa, and persistence testing in salsa at as-received and acidified pH were tested. Over the range of 1-20°C, 1°C and addition of water to the treatment package was found to improve effectiveness. The most effective treatment for green onions resulted in elimination of the virus below the detection limit (>5.5 log reduction; 350 MPa, 3 min, 1°C). D-values calculated at 300 and 350 MPa (66 s and 36 s, respectively) indicate increasing barosensitivity at higher pressures. A 300-MPa treatment in salsa for 2 minutes resulted in a 2.2-log reduction that was not dependent on pH over the range 3.8-4.0; storage trials lasting 24 and 72 h resulted in ∼0.5-log reductions, demonstrating that murine norovirus is insensitive to acidic pH both during pressure treatment and during storage. These results demonstrate the effectiveness of high pressure processing as a useful method for decontamination of green onions and salsa. In the second project, a novel combined washing and ultraviolet light process was tested to inactivate Salmonella on blueberries. This combined process was intended to both inactivate bacteria on blueberries and to prevent cross contamination by washing water. Existing static UV processes are limited by shadowing and are only effective on one surface at a time. In this study, simple water washing, UV-washing, and combined UV-sanitizer washing treatments lasting 1 and 2 minutes were tested on blueberries inoculated with a 4-strain cocktail of Salmonella . The robustness of these treatments was tested with the addition of crushed berries and blueberry juice to the washing water on skin, calyx and dip inoculated blueberries. Effectiveness of the treatments ranged from 0.74±0.55 log reduction (calyx inoculation, 1 minute, blueberry juice) to 4.91±1.56 log reduction (skin inoculation, 2 minutes, UV and chlorine in deionized water). Use of hydrogen peroxide as sanitizer reduced the risk of cross contamination and increased Salmonella inactivation on the blueberries; addition of chlorine to washing water improved effectiveness except in the presence of blueberry juice. The results of these treatments indicate that ultraviolet light is a promising technology for decontamination of blueberries when coupled with a washing process.