Masters Degrees (Food Science)

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Browsing Masters Degrees (Food Science) by Author "Ackermann, Elisma"

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    Survival and proliferation of Listeria monocytogenes in a South African ready-to-eat food factory
    (Stellenbosch : Stellenbosch University, 2017-12) Ackermann, Elisma; Gouws, Pieter Andries; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Listeria monocytogenes is a foodborne pathogen that has the ability to survive within a wide range of conditions found within food processing environments. It is the cause of a potentially life-threatening infection, listeriosis. Its presence is of major concern within ready-to-eat food processing environments and food products. Since no further processing or heat treatment is required by the consumer, post production cross contamination thereof should be minimised. Considering the lack of information about L. monocytogenes in ready-to-eat (RTE) foods in the South African context, the aim of this study was to study the survival and proliferation thereof in a RTE food factory, situated in the Western Cape, South Africa. Presumptive positive samples in the form of inoculated Rapid’L.mono plates (n=434) were collected from the factory’s Listeria management plan. Visual inspection for characteristic black colonies, provided 64 presumptive positive L. monocytogenes species. Polymerase chain reaction protocol was optimised for amplification of target genes iap (Listeria spp.) and lmo2334 (L. monocytogenes), to differentiate positive species. The Rapid’L.mono method was also evaluated for enrichment bias that cause false negatives for L. monocytogenes in the presence of L. innocua. The method was found to be sufficient for detection of L. monocytogenes, if the CFU.g-1 of both species were the same prior to enrichment. Isolates were subtyped through automated EcoRI ribotyping which was conducted using DuPont RiboPrinter® and identified as, DuPont ID 1038, DuPont ID 1041, DuPont ID 1042, and DuPont ID 18596. These strains were previously implicated in human listeriosis cases and international product recalls. DuPont ID 20243, that was isolated from the RTE factory, has not yet been logged on the global Food Microbe Tracker database. From the 29 ribotypes obtained, nine different DuPont ID’s were assigned, which was indicative of the variety of contamination sources within the RTE factory, on par with similar studies conducted. Lineage assignments of L. monocytogenes could be made using the DuPont ID’s and the RTE factory studied was found to host both lineage I and II strains. The cluster analysis revealed contaminated work boots, trolleys and crates to be possible contamination mechanisms. The response of L. monocytogenes biofilms, cultivated under flow conditions, to sanitisers used in the factory environment was evaluated. A protocol was developed using the CO2 evolution measurement system (CEMS) to evaluate the effect of four sanitisers used by the RTE food factory on L. monocytogenes biofilms. In a novel approach, it was found, that even though no bactericidal effect occurred by either sanitiser, the QAC free sanitiser resulted in the best eradication of the biofilm. Peracetic acid and QAC based chemicals had no effect on the biofilm, as recovery of L. monocytogenes was observed after multiple treatments. The RTE factory was advised to use QAC free chemical sanitisers currently available to manage biofilms, specifically in drains. This study not only created more awareness regarding the complexities of L. monocytogenes in the RTE food factory, but also laid the groundwork for further study into the survival and proliferation of L. monocytogenes in the RTE environment.