Dissertation
THERMAL RESISTANCE OF SALMONELLA IN LOW MOISTURE FOODS AS INFLUENCED BY WATER ACTIVITY AT ELEVATED TEMPERATURES
Doctor of Philosophy (PhD), Washington State University
01/2020
Handle:
https://hdl.handle.net/2376/112423
Abstract
Salmonella enterica is a major cause of foodborne illness in the United States. The thermal resistance of Salmonella increases as water activity reduces, which significantly challenges the thermal process design. There is a need to understand the relationship between the thermal resistance of Salmonella and water activity at treatment temperatures.
The objectives of this research were to: 1) improve the previous design of aluminum thermal death time cell for isothermal studies at high temperatures, 2) evaluate food components influence on water activity change at elevated temperatures, 3) study the thermal resistance of Salmonella as influenced by real-time water activity at different temperatures.
In the first study, the previous design of aluminum test cell was improved with shorter come-up time. It was easy to load and unload low-moisture food samples, and easy to seal. This improved design can provide accurate detection of microbial survival under isothermal conditions and facilitate the inactivation study for pathogen control in low-moisture foods at high treatment temperatures. In the subsequent study, the influence of major food components on water activity changes in low-moisture foods at elevated temperatures was evaluated. For a given initial water activity at 25 ºC, high-carbohydrate corn starch showed more considerable water activity increase at elevated temperatures than high-protein soy powder and high-fat coconut milk powder. Quantifying the water activity change at thermal treatment temperatures will help predict the heat resistance of bacteria in low-moisture foods. The third study utilized the improved design of test cell as an experimental tool and soy protein powder as a model food, to detect the thermal resistance of Salmonella under a wide range of real-time water activity and processing temperatures. The D-values of Salmonella showed a log-linear relationship under the real-time water activity between 0.25 and 0.70 measured at each of the treatment temperatures between 70 and 99 ºC.
This dissertation addresses some knowledge gap between the thermal resistance of Salmonella and real-time water activity in low-moisture foods, and provides advanced understanding of thermal processes for pathogen control.
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Details
- Title
- THERMAL RESISTANCE OF SALMONELLA IN LOW MOISTURE FOODS AS INFLUENCED BY WATER ACTIVITY AT ELEVATED TEMPERATURES
- Creators
- Yuqiao Jin
- Contributors
- Juming Tang (Advisor)Shyam S Sablani (Committee Member)Mei-Jun Zhu (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Biological Systems Engineering, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 113
- Identifiers
- 99900581414601842
- Language
- English
- Resource Type
- Dissertation