Many types of foods are sterilised and packaged aseptically to maximise their shelf life and ensure that they are safe for consumption. However, if even a few micro-organisms survive these treatments, the quality and/or safety of the food can be seriously compromised. Therefore, packaging materials that can actively participate in the process of inactivating micro-organisms have a potentially important role in protecting the quality and safety of packaged foods. The aim of this project is to explore the effectiveness of the photodynamic effect as a method of inactivating micro-organisms on the surface of packaging materials. Photodynamic action occurs when a photosensitiser molecule absorbs light in the presence of oxygen, leading to the formation of reactive oxygen species such as singlet oxygen, superoxide radicals, or other free radicals; these species are known to inactivate cells. Medical uses of photodynamic action have been studied extensively, usually in applications where the reactive oxygen species are produced intracellularly. However, very little research has been conducted to investigate the efficacy of extra-cellularly generated reactive oxygen species on the viability of micro-organisms, and accordingly this research project investigated the possibility that this approach might be used for inactivating micro-organisms on packaging materials. The results of this study indicate that singlet oxygen may be produced at the surface of polymer films that contain selected photosensitisers, resulting in the oxidation of known singlet-oxygen acceptors to form endoperoxides. This provides evidence that singlet-oxygen mediated reactions can occur at the surface of a sensitising film. It is likely that cell destruction is caused by singlet-oxygen, rather than involving other activated species. It was further shown that the photodynamically generated singlet-oxygen can inactivate micro-organisms (extra-cellularly) on the surface of a polymeric material. The study included examples from each genus of micro-organisms that are of concern to the food and packaging industry, including: Gram-negative bacteria (Escherichia coli); Gram-positive bacteria (Bacillus cereus), both vegetative cells and endospores; yeast (Saccharomyces cerevisiae), and mould (Fusarium oxysporium.) Results indicate that the photodynamic effect causes a substantial reduction in viable cell numbers for vegetative cells and spores (both bacterial and fungal) that have been inoculated onto a plastic surface containing the photosensitiser, anthraquinone,. The results show that an increase in the amount of reactive oxygen species produced by photodynamic action increases the inactivation rate of the micro-organisms. The micro-organisms investigated were susceptible to photodynamic action to varying extents. In conclusion, the results demonstrate that control of microbial populations on the surface of polymeric films (used in food packaging) is achievable using photodynamic action produced from polymers, based on the reported amounts of micro-organisms found on food packaging materials. / Master of Science (Hons)
| Identifer | oai:union.ndltd.org:ADTP/234225 |
| Date | January 2008 |
| Creators | Zerdin, Katherine, University of Western Sydney, College of Health and Science, School of Natural Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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