Beer stability is a critical quality parameter and a large amount of research has attempted to understand and optimise it. The present study focused on the flavour and foam aspects of beer stability and novel methods of analysis were employed to investigate the influence of yeast physiological state, pitching rates, pasteurisation methods and raw materials on these important parameters. Laser scanning confocal microscopy and flow cytometry were used to gain an in-depth understanding of physiological state and protein dynamics of brewing yeast. Yeast cell components such as glycogen, neutral lipids, trehalose, bud scars, DNA and intracellular proteinases were successfully visualised and quantified. Co-localisation studies with a yeast GFP clone expressing proteinase A (Pr A) were conducted to explore expression and excretion of Pr A in a variety of stress situations encountered during wort fermentations. Pr A plays a key role in the degradation of the hydrophobic polypeptides responsible for the beer foam stability. The impact of flash pasteurisation compared to sterile filtration on Pr A levels, hydrophobic polypeptide content and foam stability has been investigated. Another focus of this study was to elucidate the origin and fate of polypeptides, throughout wort production and fermentation. Special emphasis was placed on the changes in size and/or hydrophobicity of foam active polypeptides throughout the brewing process in order to identify stages in the process where retention of foam active polypeptides and consequently beer foam stability could be increased. It was attempted to determine what proportion of polypeptides found in beer originate from the cereals and the hops and how these polypeptides evolve throughout the brewing process. High and lower gravity beers were compared with regard to their polypeptide distribution and degree of polypeptide glycosylation. Understanding the mechanisms of beer staling is a longstanding research priority of brewers in order to extend beer shelf life. It was attempted to shed light on the mechanisms involved in beer staling, the role of Reactive Oxygen Species and their interaction with thiol groups in beer proteins. Several approaches for inhibiting or retarding oxidation of the beer matrix were explored. Novel methods for the assessment of oxidative stability and content of thiol and carbonyl groups in beer proteins were developed.

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No description available.

In recent years, some outbreaks of bacterial infection in neonatal intensive care units have been traced to powdered infant formula contaminated with Cronobacter species, causing life-threatening diseases such as necrotizing enterocolitis and meningitis. This study for the first time presents growth data and whole genome comparisons for five different species of Cronobacter after the taxonomic revision by Iversen et al. (2008). Growth data for 28 bacterial strains across 21 bacterial species in casein- and whey-dominant infant formula at temperatures 21, 27, 37, 41 and 44oC were determined, covering category A and B organisms as defined by WHO 2006. The data revealed potential of some Cronobacter species to grow at 44oC, posing a significant risk of infection by the bacterium when following the current formula preparation guidelines. The results were presented to the Food Standards Agency with the aim to update the current risk assessment model and improve infant formula preparation guidelines. The first sequenced Cronobacter genome (C. sakazakii BAA-894) was used to construct a 384,030 probe oligonucleotide tiling DNA microarray covering its 4 Mb chromosome and plasmids pESA2 (31 kb) and pESA3 (131 kb). Comparative genomic hybridization (CGH) was undertaken on five C. sakazakii strains, and representatives of four other Cronobacter species. CGH highlighted 15 clusters of genes that were divergent or absent in more than half of the tested strains. Six of these were of probable prophage origin; other regions included type VI secretion systems, the O-antigen gene locus, a tellurite resistance cluster, a fimbriae cluster, and a copper resistance operon cop. The CGH analysis highlighted the role of horizontal gene transfer, as a significant part of the variable gene pool was due to acquisition of mobile DNA. A number of genes unique to Cronobacter species associated with neonatal infections (C. sakazakii, C. malonaticus and C. turicensis) were identified. These included a copper and silver resistance operon cus linked to invasion of the blood-brain barrier by neonatal meningitic strains of Escherichia coli. By comparing the neonatal intensive care unit outbreak strains with less virulent strains and by analysis of the variable regions, we identified a list of putative virulence factors that may improve our limited understanding of Cronobacter’ s pathogenesis.

Chapati, an unleavened flat bread, is a staple in the diet in Pakistan. Wheat in the form of chapati can contribute as much as 90% of the total dietary energy intake to the rural population and generally provides more than half dietary energy and protein. Such a heavy dependence on this cereal food has led to protein malnutrition due to wheat proteins being deficient in lysine, an essential amino acid. The aim of this study was to produce savoury chapati with enhanced nutritional value. Attitudes to a variety of savoury flavours were determined in consumers of Pakistan and in immigrants to Glasgow. Chicken and meaty were most and cheesy least preferred. Amongst chapati quality characters, nutritional value was rated highest followed by flavour. These studies suggested that consumers favoured a product with appropriate flavour, a soft texture and of high nutritional value. Typically chapaties are prepared with wholemeal flours with medium rheological optima. Doughs of British wheat varieties Fresco and Galahad (33+67) and Mercia and Galahad (50+50) had moderate stickiness, high sheeting ability, and were low in shrinkage after sheeting. Such suitable mixtures yielded flours suitable for chapati production. Wheat protein profiles were determined by electrophoresis and relationships between proteins and rheological properties determined with partial least squares regression (PLS2). Dough development time was positively correlated with aggregated values of high molecular weight (HMW) and low molecular weight (LMW) glutenins, ratio of polymeric to monomeric and LMW glutenins, and negatively correlated with the total of gliadin, globulin and albumin fractions. Dough stability showed negative and tolerance index positive correlations with gliadin. Resistance to extension was associated with dough stability and inversely with gliadin content. Such studies reveal that glutenin contributes strength and gliadin imparts weakness to flour. Response surface methodology, used to optimise chapa ties , revealed that a successful savoury product could be produced by incorporating 1.5 to 2.0 % yeast extract without any deleterious effect on dough physical characteristics. Yeast extract enhanced the concentrations of protein from 13.1 % to 14.4 % in chapati. In addition to enhanced nutritional value, yeast extract imparted a desirable savoury flavour to chapati.

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Consumers demand food products that are safe, of high quality, nutritious and minimally processed. These demands are difficult to meet through the use of conventional processing technologies. Therefore, the academic and industrial sectors are exploring alternatives. Novel food processing technologies can potentially provide the means to meet consumer demands. The results of this PhD thesis contribute to the need for further information on how novel processing technologies, specifically high pressure processing, cold plasma and microwave heating, can ensure microbiological safety, and retain or improve quality and nutrient content for a very important segment of the food industry, namely, convenience foods.

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