Use of oxygen sensors for the non destructive measurement of oxygen in packaged food and beverage products and its impact on product quality and shelf life

The principal objective of this thesis was to investigate the ability of reversible optical O2 sensors to be incorporated into food/beverage packaging systems to continuously monitor O2 levels in a non-destructive manner immediately postpackaging and over time. Residual levels of O2 present in packs can negatively affect product quality and subsequently, product shelf-life, especially for O2-sensitive foods/beverages. Therefore, the ability of O2 sensors to continuously monitor O2 levels present within food/beverage packages was considered commercially relevant in terms of identifying the consequences of residual O2 on product safety and quality over time. Research commenced with the development of a novel range of O2 sensors based on phosphorescent platinum and palladium octaethylporphyrin-ketones (OEPk) in nano-porous high density polyethylene (HDPE), polypropylene (PP) polytetrafluoroethylene (PTFE) polymer supports. Sensors were calibrated over a temperature range of -10°C to +40°C and deemed suitable for food and beverage packaging applications. This sensor technology was used and demonstrated itself effective in determining failures in packaging containment. This was clearly demonstrated in the packaging of cheese string products. The sensor technology was also assessed across a wide range of packaged products; beer, ready-to-eat salad products, bread and convenience-style, muscle-based processed food products. The O2 sensor technology performed extremely well within all packaging systems. The sensor technology adequately detected O2 levels in; beer bottles prior to and following pasteurisation, modified atmosphere (MA) packs of ready-to-eat salad packs as respiration progressed during product storage and MA packs of bread and convenience-style muscle-based products as mycological growth occurred in food packs over time in the presence and absence of ethanol emitters. The use of the technology, in conjunction with standard food quality assessment techniques, showed remarkable usefulness in determining the impact of actual levels of O2 on specific quality attributes. The O2 sensing probe was modified, miniaturised and automated to screen for the determination of total aerobic viable counts (TVC) in several fish species samples. The test showed good correlation with conventional TVC test (ISO:4833:2003), analytical performance and ruggedness with respect to variation of key assay parameters (probe concentration and pipetting volume). Overall, the respirometric fish TVC test was simple to use, possessed a dynamic microbial range (104-107 cfu/g sample), had an accuracy of +/- one log(cfu/g sample) and was rapid. Its ability to assess highly perishable products such as fish for total microbial growth in <12 hr demonstrates commercial potential.

Immunostimulatory effects of different aspects of aquaculture on the host response in the edible sea urchin, paracentrotus lividus

Aquaculture is a fast-growing industry contributing to global food security and sustainable aquaculture, which may reduce pressures on capture fisheries. The overall objective of this thesis was to look at the immunostimulatory effects of different aspects of aquaculture on the host response of the edible sea urchin, Paracentrotus lividus, which are a prized delicacy (roe) in many Asian and Mediterranean countries. In Chapter 1, the importance of understanding the biology, ecology, and physiology of P. lividus, as well as the current status in the culture of this organism for mass production and introducing the thesis objectives for following chapters is discussed. As the research commenced, the difficulties of identifying individuals for repeat sampling became clear; therefore, Chapter 2 was a tagging experiment that indicated PIT tagging was a successful way of identifying individual sea urchins over time with a high tag retention rate. However, it was also found that repeat sampling via syringe to measure host response of an individual caused stress which masked results and thus animals would be sampled and sacrificed going forward. Additionally, from personal observations and discussion with peers, it was suggested to look at the effect that diet has on sea urchin immune function and the parameters I measured which led to Chapter 3. In this chapter, both Laminaria digitata and Mytilus edulis were shown to influence measured immune parameters of differential cell counts, nitric oxide production, and lysozyme activity. Therefore, trials commencing after Trial 5 in Chapter 4, were modified to include starvation in order to remove any effect of diet. Another important aspect of culturing any organism is the study of their immune function and its response to several immunostimulatory agents (Chapter 4). Zymosan A was shown to be an effective immunostimulatory agent in P. lividus. Further work on handled/stored animals (Chapter 5) showed Zymosan A reduced the measured levels of some immune parameters measured relative to the control, which may reduce the amount of stress in the animals. In Chapter 6, animals were infected with Vibrio anguillarum and, although V. anguillarum, impacted immune parameters of P. lividus, it did not cause mortality as predicted. Lastly, throughout this thesis work, it was noted that the immune parameters measured produced different values at different times of the year (Chapter 7); therefore, using collated baseline (control) data, results were compiled to observe seasonal effects. It was determined that both seasonality and sourcing sites influenced immune parameter measurements taken at different times throughout the year. In conclusion, this thesis work fits into the framework of development of aquaculture practices that affect immune function of the host and future research focusing on the edible sea urchin, P. lividus.