Thesis
The stability of Listeria monocytogenes in low-water activity matrices
Washington State University
Master of Science (MS), Washington State University
2017
Handle:
https://hdl.handle.net/2376/101508
Abstract
Listeria monocytogenes has the highest lethality of any foodborne pathogen, with a mortality rate of 20-25%. L. monocytogenes has been implicated in several outbreaks in high-and-medium-moisture food products, and is a major concern of food processors. Also of concern is Lm potential for contamination of low-moisture foods, such as flours, grains, and milk powder. Our study examined the stability of L. monocytogenes in organic pastry flour and also in four chocolate cake mix formulations. For organic flour, L. monocytogenes was equilibrated at aw 0.30, 0.45, and 0.60, then challenged at 70°C, 75°C, and 80°C for each aw level. D-values (in min) were: D70: 37.10, 19.94, and 7.08; D75: 17.44, 7.73, and 3.13 D80: 16.85, 4.61, and 1.59. Z-values for aw 0.30, aw 0.45, and aw 0.60, respectively, were (in °C): 12.86, 14.18, and 9.92. L. monocytogenes long-term stability was measured for 6 months at aw 0.30 and aw 0.60. Over six months, at 0.30 Lm decreased by 2.5 log; and at 0.56 by 6.1 log. For cake mix, mixes included commercial mix CM; commercial mix-no sugar NS; flour, cocoa, and sugar, FCS; and cocoa and flour FC. Mixes were inoculated with L. monocytogenes, equilibrated at aw 0.45, then challenged at 70°C, 75°C, and 80°C. D70, D75, and D80 values, respectively, were (in min): CM- 38.49, 21,07, 6.92; NS- 15.59, 7.05, 3.39; FCS- 24.61, 7.13, 2.42; FC- 5.87, 4.02, 2.03. z-values were (in °C): CM- 12.03; NS - 13.16; FCS- 11.06; CF- 18.93. the aw at 70°C, 75°C, and 80°C for each formulation inside thermal cells was measured with a vapor analyzer. Lower D-values corresponded to higher aw levels within each formulation. Across matrices no correlation existed between aw levels and D-values. Matrices with sugar exhibited significantly higher D-values than their non-sugar counterparts. Differences in D-values were potentially a combination of matrix composition, aw levels, and the chemical and physical effects of cocoa powder and other matrix components.
Metrics
Details
- Title
- The stability of Listeria monocytogenes in low-water activity matrices
- Creators
- Michael Hall Taylor
- Contributors
- Meijun Zhu (Degree Supervisor)Barbara Rasco (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Food Science, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525050001842
- Language
- English
- Resource Type
- Thesis