Dissertation
THE PROTECTIVE EFFECT OF OIL ON BACTERIAL THERMAL INACTIVATION IN HIGH-FAT LOW-MOISTURE FOODS: MECHANISMS AND SOLUTIONS
Doctor of Philosophy (PhD), Washington State University
01/2020
Handle:
https://hdl.handle.net/2376/116870
Abstract
High-fat low-moisture foods like peanut butter and tahini are often implicated in outbreaks of Salmonella spp. Recent studies indicate that the fat content in foods may have a protective effect on the bacteria from thermal processing. Existing evidence implies that temperature rise in oil may increase the water solubility of oil and therefore desiccate the bacteria inside. The objectives of this research were to 1) understand how water activity changes in oil with temperature, 2) study the effect of water activity of oil on the thermal resistance of bacteria, and 3) evaluate the effect of humid heat on the thermal inactivation rate of bacteria in oil.
First, a method was developed to measure the water activity of oil directly at elevated temperatures. Results showed that the water activity of oil decreased sharply (exponentially) with the increasing temperature which confirmed that bacteria in oil are exposed to a desiccated environment in thermal processing. Secondly, the thermal resistance of E. faecium in peanut oil of different water activities was tested within closed capillary tubes at 80°C. The results showed that the D-value of E. faecium reduced exponentially with the increasing aw of oil. The similarity between the thermal resistance of E. faecium in oil and that in dry air suggests that oil protects bacteria from thermal treatments through desiccation. Thirdly, the thermal resistance of E. faecium was studied in very thin oil layers (0.51, 0.26, and 0.10 mm) under controlled relative humidities (0-100%) at 80 °C. The results demonstrated a sharply reduced thermal resistance of E. faecium in oil within a humid environment. But a significant effect of sample thickness was observed which indicates that the slow diffusion of moisture in oil protects bacteria from humid heat.
In conclusion, oil protects bacteria from thermal inactivation through the desiccation effect. In a high humid environment, oil can also act as a moisture barrier that slows down the rehydration of the bacteria. This dissertation has filled the knowledge gap in understanding the thermal death behavior of bacteria in a complex food matrix which may benefit the development of thermal processes of high-fat low-moisture foods.
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Details
- Title
- THE PROTECTIVE EFFECT OF OIL ON BACTERIAL THERMAL INACTIVATION IN HIGH-FAT LOW-MOISTURE FOODS: MECHANISMS AND SOLUTIONS
- Creators
- Ren Yang
- Contributors
- Juming Tang (Advisor)Shyam S. Sablani (Committee Member)Girish M. Ganjyal (Committee Member)Stephen P. Lombardo (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
- 150
- Identifiers
- 99900581411501842
- Language
- English
- Resource Type
- Dissertation