Improved detection techniques for foodborne pathogens: Separation techniques using crossflow microfiltration

Separation and concentration of microorganisms in foods have been suggested as an alternative to enrichment culture as a pre-analytical step of detection in accordance with the need of a truly real-time technique for foodborne pathogen detection. Directly concentrating and recovering cells from food matrices is difficult due to the heterogeneous nature of foods and there is a lack of methods to cope with this difficulty. As a remedy to this problem, this dissertation proposed a new protocol to concentrate and recover microorganisms in a time-efficient manner from food-derived suspensions to quantitate low levels of cells. This protocol includes sampling from food by homogenization, enzymatic pretreatment of crude food homogenates, pre-filtration, and cell concentration and recovery using a cell concentration instrument. One challenge for this work is that the components in crude food derived suspensions may cause serious fouling of membrane. Accordingly, the extraction conditions for food samples such as the mechanical force used in homogenization and pre-filtration of the extract are studied to minimize the release of food components while maintaining bacterial viability. Enzymatic pretreatment and pre-filtration are proposed to clarify the crude food suspensions. The principle of the cell concentration instrument is based on processing the treated food suspensions by microfiltration operated in a crossflow configuration to reduce the sample volume and increase the concentration of microbial cells to a detectable level so that they may be effectively probed for the presence of pathogens. This work evaluates the efficiency of the cell concentration instrument in concentrating and recovering artificially spiked Salmonella Enteritidis from aqueous chicken homogenates. The concentration and recovery of naturally occurring microbiota in chicken samples is also discussed. In addition, from a process economics point of view, it is important to reuse membranes. In this work, a hydraulic and chemical cleaning procedure is introduced, and the cleaning efficiency is studied in terms of system sanitation and recovery of membrane permeability. Finally, a mathematical model is developed to describe the fouling process and filtration behavior as a function of feed suspension properties, operating conditions and the geometric parameters of the membrane module. A model-based analysis of membrane design is then carried out to achieve reduced fouling and improved filtration performance. This work translates engineering fundamentals of crossflow microfiltration into operational conditions for a hollow fiber-based microfiltration of food extracts. This thesis addresses the hypothesis that a combination of extract pretreatment and hollow fiber operating conditions enables reproducible recovery of pathogens for purposes of detecting their presence in meat