The main objective of this study was to determine the pressure induced inactivation mechanism of pressure-resistant Escherichia coli O157:H7 933 and Staphylococcus aureus 485 in a low acid food.
Firstly, inactivation curves of pathogens were obtained at 200 to 400 MPa at 40º / C in peptone water and carrot juice. First-order and Weibull models were fitted and Weibull model described the inactivation curves of both pathogens more
accurately than first-order model, revealing that food systems could exhibit either protective or sensitizing effect on microorganisms. Carrot juice had a protective effect on E. coli O157:H7 whereas it had a sensitizing effect on S. aureus, due to the naturally occurring constituents or phytoalexins in carrot roots that could have a toxic effect.
Secondly, scanning electron microscopy (SEM) and fluorescent microscopy images of studied pathogens were taken. Developed software was used to analyze
SEM images to calculate the change in the view area and volume of cells.
Membrane integrity of pressurized cells was also examined using fluorescent microscopy images. The increase in average values of the view area and volume of both pathogens
was significant for the highest pressure levels studied. The increase in volume and the view area could be explained by the modification of membrane properties, i.e., disruption or increase in permeability, lack of membrane integrity,
denaturation of membrane-bound proteins and pressure-induced phase transition of membrane lipid bilayer. The change in volume and the view area of microorganisms added another dimension to the understanding of inactivation
mechanisms of microbial cells by HHP.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12609205/index.pdf |
| Date | 01 December 2007 |
| Creators | Pilavtepe, Mutlu |
| Contributors | Alpas, Hami |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Ph.D. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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