Dissertation
INFLUENCE OF WATER ACTIVITY ON THE THERMAL RESISTANCE OF SALMONELLA IN LOW-MOISTURE FOODS
Doctor of Philosophy (PhD), Washington State University
01/2017
Handle:
https://hdl.handle.net/2376/111357
Abstract
Persistence of foodborne pathogens such as Salmonella in low-moisture foods (LMF) and its survival through thermal treatments and storage has caused a worldwide concern. In LMF, water activity (aw) influences the thermal resistance (D-value) of Salmonella. In previous studies on the D-values of Salmonella in LMF, inoculated LMF were treated in sealed test-cells/pouches at high temperatures while aw of LMF at the room temperature was reported. However, aw of LMF (at constant moisture content) in an enclosed system changes with the temperature, which may increase or decrease based on the sorption isotherms. But, there are limited aw measurement techniques at the elevated temperatures.
In first study, a novel test-cell (TAC) was developed to evaluate the isolated influence of aw on the D-value of Salmonella in LMF. In TAC, stable relative-humidity (RH) (aw of LMF) was maintained at the elevated temperatures by using LiCl solutions of specific molality. D-values of Salmonella in organic wheat flour (OWF) under controlled RH environments were evaluated against the conventional thermal death time (TDT) cells. Results demonstrated that the stable aw in TAC significantly increased D-value of Salmonella in OWF (p <0.05) compared to data from TDT cells where aw of OWF varied according to sorption isotherms.
In subsequent study, an improved test-cell (TAC II) was developed with increased sample exposure area (by 490%) and reduced sample depth (by 83%) compared to TAC. TAC II reduced the equilibration time for LMF (< 4 min) with headspace RH during thermal treatments compared to TAC (> 10 min). D-values of Salmonella in OWF from TAC II were observed to be significantly higher than the data from TAC and TDT cells (p <0.05).
Lastly, an improved thermal-cell with a RH-temperature sensor was used to measure aw of three LMF at constant moisture content for a wide-temperature range. At a fixed moisture content, aw of LMF generally increased with the temperature. An exponential relationship was observed between the net isosteric-heats of sorption and moisture contents of LMF.
This dissertation addresses some of the knowledge gaps associated with the influence of aw at elevated temperatures on D-values of pathogens in LMF.
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Details
- Title
- INFLUENCE OF WATER ACTIVITY ON THE THERMAL RESISTANCE OF SALMONELLA IN LOW-MOISTURE FOODS
- Creators
- Ravi Kiran Tadapaneni
- Contributors
- Juming Tang (Advisor)Shyam S. Sablani (Committee Member)Meijun Zhu (Committee Member)Girish Ganjyal (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
- 154
- Identifiers
- 99900581426101842
- Language
- English
- Resource Type
- Dissertation