Modelling dairy biofilms for targeted control of thermophilic bacteria
Li, Isabel Huizi
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Biofilms are the main source of bacterial contamination in dairy manufacturing plants. Strategies to mitigate biofilm development in dairy manufacture aim to improve the microbiological quality of the products manufactured and to maximize the run length of manufacturing plants, and thereby obtain substantial economic benefits. A simple strategy involves creating an unstable environment for microbial growth by manipulating conditions, such as temperature, on a sufficiently frequent basis to disrupt biofilm growth while maintaining the ability to manufacture high quality products. Thermophilic bacilli, Geobacillus stearothermophilus and Anoxybacillus flavithermus, are the main contaminants responsible for economic loss in milk powder production all over the world, colonising plant and persisting through cleaning. Because of the significant economic loss caused by thermophilic biofilms, there is an urgent need to study these bacteria. In my research I investigated the hypothesis that a mathematical model can represent the growth of these thermophilic bacteria as biofilms in milk powder plants and whether the model can be used to optimise methods to control these bacteria. A novel technology, called temperature cycling, was studied in depth in this research, involving creating an unstable environment for microbial growth by manipulating the temperature, on a sufficiently frequent basis to disrupt biofilm growth, while limiting the amount of dangerous chemicals used for cleaning and maintaining the ability to manufacture dairy products hygienically. Robust and practical models were designed based on the logistic growth equation for a laboratory scale milk heating plant. The models can be run without recourse to extensive computing power and can be used in the dairy industry as decision making tools, which can provide instantaneous prediction of the thermophile level of the product for a known level of incoming thermophilic bacteria.