With modern culture moving towards convenience in terms of fresh produce, especially with meat products, science needs to constantly evolve to serve these customer needs. These needs however can sometimes be implemented too hastily without the proper assessment done for factors such as food safety. One such improvement is the use of modified atmosphere packaged minced meat. This form allows the minced meat to be kept for much longer than normal without freezing the product, providing the fast pasted consumer both the convenience of having fresh, unfrozen meat as well as an added shelf life. MAP works by disrupting the atmosphere within these packages, retarding the growth of the spoilage micro-organisms, thus causing them to require a longer time span to reach spoilage numbers. The problem however arises that although most of these techniques are tried and trusted on the products’ spoilage organisms, it does not take into consideration the effect MAP and the altered spoilage organism communities would have on a pathogen that might be present on the products. This study thus aimed to assess the effect of both factors on Escherichia coli O157:H7 (phase 1) and Staphylococcus aureus (phase 2) in minced meat kept at 5°C as well as trying to identify the major affecting factors. The two subject organisms were each inoculated into 2 different types of MAP packs and a non-atmosphere modified PVC overlaid minced meat sample at two differing concentrations of 105 and 102 to also assess the impact of high andlow initial pathogen presence. These packs were then analysed over a time period of 16 days to track the changing minced meat environment. APC, Pseudomonads, LAB and Enterobacteriaceae counts were all investigated along with the pathogenic counts. Apart from colony enumeration, the colour of the minced meat samples were also taken to determine the effect that these parameters have on the appearance of the product, as colour is often the first sensorial characteristic that determines the purchase of fresh meat products. pH was determined to ascertain the environmental changes occurring in the product and whether groups such as the LAB would change the environment to better suit their needs. Finally the atmospheric makeup was also measured to determine the effect of the MAP system and the change occurring in a closed system that could be attributed to the growth and respiration of the bacterial communities present. Apart from the main aim of the study, two additional studies were performed that arose during the planning and analyses of the two primary phases. Firstly the use of a quarter versus a full plate enumeration was studied to determine its accuracy as well as possibility of use in full studies to aid enumeration and decrease time and financial input. Here a direct comparison was done between the two techniques after which they were compared and assessed in their functionality for both homogenous and heterogeneous community enumeration on selective and non-selective media. The other secondary study focussed on the use of new technology for both the enumeration and tracking of genetically modified organisms in a variety of different environments. Here a bioluminescent imaging system was used on a genetically modified strain of E. coli to track its spread through minced meat, packaged either in a MAP or PVC overlaid pack, over 48 hours in an accelerated shelf life study. Enumeration of said organism was also undertaken whereby the intensity of emitted light would correspond to a defined count, enabling rapid enumeration of samples, whether overgrown or not. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Food Science / unrestricted

The aim of this thesis is to investigate the dynamical behaviors of spatially extended systems with fluctuating time delays. In recent years, the study of spatially extended systems and systems with fluctuating delays has experienced a fast growth. In ubiquitous natural and laboratory situations, understanding the action of time-delayed signals is a crucial for understanding the dynamical behavior of these systems. Frequently, the length of the delay is found to change with time. Spatially extended systems are widely studied in many fields, such as chemistry, ecology, and biology. Self-organization, turbulence, and related nonlinear dynamic phenomena in spatially extended systems have developed into one of the most exciting topics in modern science. The first part of this thesis considers the discrete system. Diffusively coupled map lattices with a fluctuating delay are used in the study. The uncoupled local dynamics of the considered system are represented by the delayed logistic map. In particular, the influences of diffusive coupling and fluctuating delay are studied. To observe and understand the influences, the results for the considered system are compared with coupled map lattices without delay and with a constant delay as well as with the uncoupled logistic map with fluctuating delays. Identifying different patterns, determining the existence of traveling wave solutions, and specifying the fully synchronized stable state are the focus of this part of the study. The Lyapunov exponent, the master stability function, spectrum analysis, and the structure factor are used to characterize the different states and the transitions between them. The second part examines the continuous system. The delay is introduced into the reactionterm of the Fisher-KPP equation. The focus of this part of study is the time-delay-induced Turing instability in one-component reaction-diffusion systems. Turing instability has previously only been found in multiple-component reaction-diffusion systems. However, this work demonstrates with the help of the stability exponent that fluctuating delay can result in Turing instability in one-component reaction-diffusion systems as well. / Ziel der vorliegenden Arbeit ist die Untersuchung der Einflüsse der zeitlich fluktuierenden Verzögerungen in räumlich ausgedehnten diffusiven Systemen. Durch den Vergleich von Systemen mit konstanter Verzögerung bzw. Systemen ohne räumliche Kopplung erhält man ein tieferes Verständnis und eine bessere Beschreibungsweise der Dynamik des räumlich ausgedehnten diffusiven Systems mit fluktuierenden Verzögerungen. Im ersten Teil werden diskrete Systeme in Form von diffusiven Coupled Map Lattices untersucht. Als die lokale iterierte Abbildung des betrachteten Systems wird die logistische Abbildung mit Verzögerung gewählt. In diesem Teil liegt der Fokus auf Musterbildung, Existenz von Multiattraktoren und laufenden Wellen sowie der Möglichkeit der vollen Synchronisation. Masterstabilitätsfunktion, Lyapunov Exponent und Spektrumsanalyse werden benutzt, um das dynamische Verhalten zu verstehen. Im zweiten Teil betrachten wir kontinuierliche Systeme. Hier wird die Fisher-KPP Gleichung mit Verzögerungen im Reaktionsteil untersucht. In diesem Teil liegt der Fokus auf der Existenz der Turing Instabilität. Mit Hilfe von analytischen und numerischen Berechnungen wird gezeigt, dass bei fluktuierenden Verzögerungen eine Turing Instabilität auch in 1-Komponenten-Reaktions-Diffusionsgleichungen gefunden werden kann