In this thesis, the OU methodology was the principal technique usefd to investigate the fitness-for-purpose of the samplmg of food and animal feed. The Optimised Uncertainty (OU) methodology balances the potential financial consequences due to misclassification of food commodities, against the costs of measurements by identifying the optimal level of uncertainty.

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The first aim of this research was to evaluate recently developed biosensors for their potential to detect chemical contaminants, chloramphenicol and/or nitrofuran metabolites and, overall their potential for the food industry in their present form, or with further development. The biosensors evaluated were the dotLab® system (Axela Inc., Toronto, Canada), SPRi-Lab+™ system (Horiba Scientific, Stanmore, UK) and Octet® RED96 system (ForteBio Inc., California, USA). All three were able to detect the chosen chemical contaminants in the form of either single- or multi-analyte detection, or both, with two systems, the SPRi-Lab+™ and Octet® RED96, achieving sensitivities equivalent to current minimum required performance limits. The ability to use crude matrices with the Octet® RED96 system, and the additional multiplexing features of both the SPRi-LabFM and Octet® RED96 systems, makes them prospective biosensors in their current form. Pending further development of the dotLab® system's multiplexing features this could be applicable to the dotLab® system also. The second aim of this research was to advance detection methods for two major foodborne pathogens, Salmonella spp. and Listeria monocytogenes, by screening for and employing highly bacteria-specific phage. A novel phage display-derived peptide binder, Peptide MSal020417 with sequence NRPDSAQFWLHH, was identified which results suggest is a genus-specific anti-Salmonella antibody mimicking peptide. A novel phage display-derived phage clone was identified which results suggest is highly specific for L. monocytogenes. These highly specific pathogen binders could be employed in •1 any detection method that traditionally employs an antibody, with the aim to advance the speed and specificity of detection of these foodborne pathogens.

Acrylamide is a genotoxic compound produced in foods probably through the Maillard reaction. Acrylamide undergoes processes during cooking that leads to its loss. The aim of this research is to acquire knowledge on the mechanisms of acrylamide loss using kinetic studies, and to incorporate this knowledge in a broader kinetic model. Particular attention is placed on the Michael addition reaction, i.e., the reaction of the vinyl group of acrylamide with amino or sulfhydryl groups. Two model systems have been used for the study of the kinetics of acrylamide loss: an aqueous system and a dry solid system. The aqueous system has provided information on the Michael addition reaction of acrylamide with amino acids, with particular emphasis on glycine and proline, which were found to have the highest rates of reaction. Experiments on the dry solid system have shown that other reactions pathways different than the Michael addition might take place in foods in conjunction with amino dependent reactions. A mechanism based on the crystallisation of the amino acids has been proposed to explain the kinetic behaviour observed. To try to increase our understanding on the Michael addition reaction, ab initio methods and molecular mechanics have been employed for the investigation of an acrylamide-glycine reaction. Furthermore, multiresponse modelling has been employed on the development of a kinetic model for acrylamide formation and loss using data from the heating of potato, rye, and wheat cakes heated at 180 QC. This model can be used for the prediction of the formation and loss of acrylamide in foods.

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No description available.

Listeria monocytogenes is a facultative intracellular pathogen and the causative agent of listeriosis. Contaminated food is thought to be the major vector of listeriosis. Food products that have been implicated in cases of listeriosis include poultry, meat, seafood, milk and their derivative products. Microbial contamination of food surfaces is an ongoing problem for the food industry and is a major risk to food quality and safety. The primary aim of this study is to investigate attachment of L. monocytogenes 10403S to different food processing surface materials. The mean number of cells recovered from short contact times and 2 hour contact times of coupons in bacterial culture significantly differ for each of the 18 materials examined with the exception of polypropylene. L. monocytogenes transposon mutants were generated and a cellular staining assay was used for screening, selecting for those mutants attaching to glass coverslips in low frequency. One mutant was investigated further. An ORF disrupted by transposon mutagenesis in this mutant showed 48% identity to the L. monocytogenes strain EGD alpha-mannosidase and a conserved domain belonging to the glycosyl hydrolase family (alpha-mannosidases). An enzyme assay confirmed that expression of this enzyme was reduced in the mutant. Alpha-mannosidase is part of the alginate pathway characterized in Pseudomonas aeruginosa. Alginate activity has been shown to be up-regulated during attachment of P. aeruginosa to materials (Davies et al., 1993) and is implicated in bacterial attachment to surfaces and biofilm formation. We therefore suggest a hypothesis that interrupting an ORF coding for an alpha-mannosidase enzyme disrupts the alginate synthesis pathway responsible for extracellular polysaccharide (EPS) production and hence inhibits attachment to food processing surfaces. Further experiments such as site-directed mutagenesis are required to test this hypothesis.

Aerated foods are an important sector of the processed food market, but they are poorly characterised by the available techniques. Ultrasound has a complex interaction with bubbly liquids, which has the potential to be used as a means of non- destructively characterising bubbly food liquids. The ultrasonic velocity, attenuation coefficient and reflection coefficient can be related to the volume fraction of gas and bubble size distribution using theories which are known to work at low volume fraction. Ultrasonic equipment has been described which can measure the ultrasonic velocity and attenuation coefficient very accurately, and which can make reflection measurements on systems which defy transmission measurements. A dilute model bubbly system, a concentrated model bubbly system, yogurt, cream, bread dough and beer foam have been characterised ultrasonically, and by densitometry, light microscopy, electron microscopy and light scattering. The model system has been shown to be stabilised by an unusual and novel structured surfactant layer at the interface. Conventional measurements on the dilute model system did not agree with ultrasonic transmission measurements. The ultrasonic technique was able to measure volume fractions as low as 10'7, but it could not measure the bubble size. Reflection measurements on the concentrated bubbly liquid demonstrated that the theory fails at high volume fractions of air. The ultrasonic technique has been shown to be able to measure the bubble size in whipped yogurt. The presence of an agglomerated fat globule network has been shown to have a dramatic effect on the ultrasonic properties of whipped cream. The ultrasonic technique was able to discriminate between conventional whipped cream and spray cream, and the technique has been shown to be sensitive to the time-dependent properties of spray cream. The small volume fraction of air present in unfermented dough was detected by the ultrasonic reflection technique. Fermented dough could not be characterised ultrasonically. Marked inter sample variability was demonstrated in measurements on beer. The ultrasonic technique was of limited use for characterising beer foam. Realisation of the full potential of ultrasound for characterising real aerated foods will not be possible without an improved theory for concentrated systems.

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No description available.