Il existe un intérêt croissant pour le développement de levures S. cerevisiae œnologiques à rendement abaissé de conversion des sucres en alcool. Nous proposons ici une approche originale basée sur la réorientation du flux carboné vers la voie des pentoses phosphate (VPP). Dans un premier temps, nous avons montré que le flux à travers la VPP est limité par le niveau de réoxydation du NADPH et par la capacité de la voie elle même. Nous avons ensuite mis en évidence le rôle crucial du facteur de transcription Stb5 dans le maintien d'un flux basal à travers la VPP. La surexpression de STB5, couplée à l'introduction d'un système de réoxydation du NADPH, est une stratégie intéressante pour amplifier le flux à travers la VPP. En parallèle, une stratégie d'évolution dirigée basée sur l'adaptation des souches sur gluconate, un hexose mal assimilé et incorporé au niveau de la VPP, a été développée. Des souches évoluées présentant une meilleure assimilation du gluconate ont été obtenues après 70, 180 et 240 générations. En fermentation, ces souches produisent la même quantité d'éthanol que la souche parentale mais présentent des phénotypes complètement nouveaux, en particulier des performances fermentaires accrues, de faibles besoins en azote, une production d'acétate réduite et une forte production de composés aromatiques. L'analyse 13C-flux et transcriptomique d'une souche évoluée ECA5 révèle une amplification de la VPP d'un facteur 1.5 par rapport à la souche parentale EC1118, en lien avec la surexpression de GND1 et TKL1. L'expression de nombreux gènes du métabolisme azoté et de la voie Ehrlich, de l'homéostasie des protons et de la glycolyse est augmentée chez ECA5, alors que les gènes de stress et de la respiration sont globalement réprimés, de façon cohérente avec les phénotypes observés. Outre le développement de nouvelles souches d'intérêt œnologique, ce travail apporte un éclairage nouveau sur le fonctionnement de la VPP et sur ses liens avec le métabolisme central et secondaire / There is an ever-growing interest in the development of S. cerevisiae wine yeast strains with reduced ethanol yield. We proposed a novel approach based on rerouting the carbon flux towards the pentose phosphate (PP) pathway. First, we showed that the flux through the PP pathway is limited both by the absence of a mechanism for reoxidation of NADPH and by the intrinsic capacity of the pathway. We also showed that the transcription factor Stb5 plays a key role in maintaining a basal flux through the PP pathway to meet the requirements for NADPH and biosynthetic precursors. Over-expression of STB5 is a potentially useful strategy for increasing the flux through the PP pathway, provided that an alternative system of reoxidation of NADPH is expressed. In parallel, we investigated an evolutionary engineering strategy based on long-term batch culture on gluconate, a substrate poorly assimilated by S. cerevisiae cells and metabolized by the PP pathway. We selected strains that had evolved a greater gluconate consumption capacity after 70, 180 and 240 generations. During wine fermentation, these evolved strains produced similar amounts of ethanol as the parental strain but displayed completely novel phenotypes, including higher fermentation rates, lower nitrogen requirements, lower levels of acetate production, and enhanced production of aroma compounds. 13C flux analysis and transcripomic analysis of one of these strains, ECA5, showed a greater flux through the PP pathway consistent with the observed increased expression of GND1 and TKL1. The expression of genes associated with nitrogen metabolism, the Ehrlich pathway, proton homeostasis and glycolysis was stronger than in the parental strain, whereas genes involved in stress response and respiration were down-regulated, in agreement with the phenotypes of ECA5. In addition to providing strains with considerable potential for wine making, this work sheds new light on the operation of PP pathway and its links with central and secondary metabolism

Processos industriais de polimerização em emulsão são usualmente realizados em reatores tipo tanque agitado em batelada (ou semi-batelada) ou em contínuo (CSTR). Reatores contínuos tem a vantagem de serem comparativamente de menor porte, e propiciarem melhor controle da qualidade do produto pela redução de variações de batelada a batelada. Reatores tipo CSTR podem exibir oscilações periódicas e autosustentadas de conversão, de tamanho e concentração de partículas. Estas oscilações podem ser minimizadas nos reatores tubulares pulsados devido à diminuição da dispersão axial em relação aos reatores do tipo CSTR. Na presente tese, desenvolveu-se um novo tipo de reator tubular, a Coluna Pulsada de Pratos Perfurados, CPPP, para uso no processo de polimerização contínua do acetato de vinila em emulsão. O reator é operado com escoamento pulsado e contém pratos perfurados como dispositivos internos. Inicialmente foram realizados ensaios de distribuição de tempos de residência, em um reator montado em vidro, com o objetivo de caracterizar o escoamento no reator CPPP quanto ao grau de mistura axial. Os dados foram interpretados usando o modelo de escoamento pistonado com dispersão axial. Valores do coeficiente de dispersão axial foram medidos e correlacionados para diferentes condições de freqüência e amplitude de pulsação, vazão, espaçamento entre pratos, e viscosidade do fluido. Verificou-se que o grau de mistura axial pode ser variado em faixas relativamente amplas pela manipulação da freqüência e amplitude de pulsação. Foi também montado um reator em aço inox e encamisado, com as mesmas dimensões, onde foram realizados ensaios de polimerização em emulsão de acetato de vinila, medindo-se a conversão e a distribuição de tamanhos de partículas (DTP), na saída do reator em regime transiente e permanente, e também ao longo do reator em regime permanente. Verificou-se que as condições operacionais (tempo médio de residência e grau de dispersão axial) influenciam várias características do produto, como, a conversão, tamanho médio e concentração de partículas, porém, não influencia, significativamente, a viscosidade da emulsão produzida, para a receita da reação de polimerização e as condições operacionais estudadas. Os resultados experimentais foram interpretados usando um modelo matemático do reator, o qual foi estabelecido com base em um modelo cinético publicado na literatura para o processo de polimerização em emulsão de acetato de vinila em batelada. Tal modelo foi adaptado incluindo-se os termos convectivos e dispersivos nas equações de balanço de massa, e resolvido numericamente. Foram ajustados apenas dois parâmetros neste modelo, para todas as condições operacionais estudadas e os resultados simulados reproduziram adequadamente o comportamento das principais variáveis de processo para a condição de regime permanente. O novo tipo de reator contínuo apresentado neste trabalho mostrou-se ser possível obter altas conversões em tempos médios de residência da ordem ou mesmo inferiores aos do processo em batelada e atingir regime permanente de operação em um a dois tempos médios de residência. O reator é eficiente, robusto, construtivamente simples, de fácil limpeza e manutenção, e mostrou-se promissor para utilização industrial em processo de polimerização em emulsão de acetato de vinila. / Industrial emulsion polymerization processes are usually carried out in stirred tanks operated in batch/semibatch or in continuous mode (CSTR). In comparison to batch processes, continuous reactors present several advantages such as lower volumes and better quality control by reducing batch-to-batch variations. Continuous emulsion polymerization in CSTR may exhibit sustained oscillations in conversion, particle size and particle concentration. Such oscillations may be reduced in pulsed tubular reactors due to less axial mixing. In this thesis a new type of tubular reactor, called Pulsed Sieve Plate Column, PSPC, was developed for the continuous process of vinyl acetate emulsion polymerization. This reactor is operated using oscillatory pulsed flow and uses perforated plates as internals. Residence time distribution runs were carried out in a glass reactor in order to characterize the axial mixing and flow patterns in the PSPC. The data were treated using the axially dispersed plug flow model. Axial dispersion coefficient was measured for different conditions of pulse frequency and amplitude, flow rate, plate spacing and viscosity. It was found that the degree of axial mixing can be varied in wide ranges by manipulating pulsation frequency and/or amplitude. Vinyl acetate continuous emulsion polymerization runs were carried out in a jacketed stainless steel reactor (with the same size of the glass reactor). Monomer conversion and particle size distribution was measured both at the reactor exit in transient state and along the reactor length at steady-state. It was found that average residence time and degree of axial mixing affect process and product quality variables, such as monomer conversion, mean particle size and concentration, but did not affect the viscosity of the emulsion produced, for the recipe and conditions used. A mathematical model for the reactor was developed. The model used, based on a well-known kinetic model previously developed in the literature for batch emulsion polymerization, was adapted to the continuous tubular reactor by adding the dispersion and convective terms to the balance equations. The model was numerically solved. Only two parameters were adjusted in this model and the simulated results showed excellent agreement with the experimental results, for steady state conditions. The proposed tubular reactor allows to reach high monomer conversion with similar or even lower residence time than those in batch processes and reaches steady state operation in just one to two mean residence times. The reactor is efficient, easy-to-built, easy-to-clean, robust and promising for use in industrial continuous emulsion polymerization of vinyl acetate.

Processos industriais de polimerização em emulsão são usualmente realizados em reatores tipo tanque agitado em batelada (ou semi-batelada) ou em contínuo (CSTR). Reatores contínuos tem a vantagem de serem comparativamente de menor porte, e propiciarem melhor controle da qualidade do produto pela redução de variações de batelada a batelada. Reatores tipo CSTR podem exibir oscilações periódicas e autosustentadas de conversão, de tamanho e concentração de partículas. Estas oscilações podem ser minimizadas nos reatores tubulares pulsados devido à diminuição da dispersão axial em relação aos reatores do tipo CSTR. Na presente tese, desenvolveu-se um novo tipo de reator tubular, a Coluna Pulsada de Pratos Perfurados, CPPP, para uso no processo de polimerização contínua do acetato de vinila em emulsão. O reator é operado com escoamento pulsado e contém pratos perfurados como dispositivos internos. Inicialmente foram realizados ensaios de distribuição de tempos de residência, em um reator montado em vidro, com o objetivo de caracterizar o escoamento no reator CPPP quanto ao grau de mistura axial. Os dados foram interpretados usando o modelo de escoamento pistonado com dispersão axial. Valores do coeficiente de dispersão axial foram medidos e correlacionados para diferentes condições de freqüência e amplitude de pulsação, vazão, espaçamento entre pratos, e viscosidade do fluido. Verificou-se que o grau de mistura axial pode ser variado em faixas relativamente amplas pela manipulação da freqüência e amplitude de pulsação. Foi também montado um reator em aço inox e encamisado, com as mesmas dimensões, onde foram realizados ensaios de polimerização em emulsão de acetato de vinila, medindo-se a conversão e a distribuição de tamanhos de partículas (DTP), na saída do reator em regime transiente e permanente, e também ao longo do reator em regime permanente. Verificou-se que as condições operacionais (tempo médio de residência e grau de dispersão axial) influenciam várias características do produto, como, a conversão, tamanho médio e concentração de partículas, porém, não influencia, significativamente, a viscosidade da emulsão produzida, para a receita da reação de polimerização e as condições operacionais estudadas. Os resultados experimentais foram interpretados usando um modelo matemático do reator, o qual foi estabelecido com base em um modelo cinético publicado na literatura para o processo de polimerização em emulsão de acetato de vinila em batelada. Tal modelo foi adaptado incluindo-se os termos convectivos e dispersivos nas equações de balanço de massa, e resolvido numericamente. Foram ajustados apenas dois parâmetros neste modelo, para todas as condições operacionais estudadas e os resultados simulados reproduziram adequadamente o comportamento das principais variáveis de processo para a condição de regime permanente. O novo tipo de reator contínuo apresentado neste trabalho mostrou-se ser possível obter altas conversões em tempos médios de residência da ordem ou mesmo inferiores aos do processo em batelada e atingir regime permanente de operação em um a dois tempos médios de residência. O reator é eficiente, robusto, construtivamente simples, de fácil limpeza e manutenção, e mostrou-se promissor para utilização industrial em processo de polimerização em emulsão de acetato de vinila. / Industrial emulsion polymerization processes are usually carried out in stirred tanks operated in batch/semibatch or in continuous mode (CSTR). In comparison to batch processes, continuous reactors present several advantages such as lower volumes and better quality control by reducing batch-to-batch variations. Continuous emulsion polymerization in CSTR may exhibit sustained oscillations in conversion, particle size and particle concentration. Such oscillations may be reduced in pulsed tubular reactors due to less axial mixing. In this thesis a new type of tubular reactor, called Pulsed Sieve Plate Column, PSPC, was developed for the continuous process of vinyl acetate emulsion polymerization. This reactor is operated using oscillatory pulsed flow and uses perforated plates as internals. Residence time distribution runs were carried out in a glass reactor in order to characterize the axial mixing and flow patterns in the PSPC. The data were treated using the axially dispersed plug flow model. Axial dispersion coefficient was measured for different conditions of pulse frequency and amplitude, flow rate, plate spacing and viscosity. It was found that the degree of axial mixing can be varied in wide ranges by manipulating pulsation frequency and/or amplitude. Vinyl acetate continuous emulsion polymerization runs were carried out in a jacketed stainless steel reactor (with the same size of the glass reactor). Monomer conversion and particle size distribution was measured both at the reactor exit in transient state and along the reactor length at steady-state. It was found that average residence time and degree of axial mixing affect process and product quality variables, such as monomer conversion, mean particle size and concentration, but did not affect the viscosity of the emulsion produced, for the recipe and conditions used. A mathematical model for the reactor was developed. The model used, based on a well-known kinetic model previously developed in the literature for batch emulsion polymerization, was adapted to the continuous tubular reactor by adding the dispersion and convective terms to the balance equations. The model was numerically solved. Only two parameters were adjusted in this model and the simulated results showed excellent agreement with the experimental results, for steady state conditions. The proposed tubular reactor allows to reach high monomer conversion with similar or even lower residence time than those in batch processes and reaches steady state operation in just one to two mean residence times. The reactor is efficient, easy-to-built, easy-to-clean, robust and promising for use in industrial continuous emulsion polymerization of vinyl acetate.

Assessement of effects of cadium chloride exposure on the anaphylaxis reaction to food was done on six week old Swiss and BALB/c female mice. The animals were exposed to cadium as cadium chloride for either three days or six weeks. Intra-peritonal dose of cadium chloride was injected once a day, five days per week for three successive weeks. The animals were then sensitised to cow's milk by force-feeding with cow's milk for three consecutive days. Oral exposure of mice to a high dose of cadium resulted in cytotoxicity of liver and kidney cells. Retardation in growth rate and haematology change were detected. Proliferative response to the T-cell epitope from the circumsporozoite protein of plasmodium falsiparum was decreased in cultures of lymph node cells from cadium chronically treated mice and sensitised with the same peptide. In contrast, an increase of cell proliferation was observed when cow's milk was used instead. Significant increase in Immunoglobulin E level and Anaphylactic reaction dependent on the quantity of cadium exposed were recorded. No protective effect of ascorbic acid or zinc acetate on cadium alteration of immune response was observed / Master of Science (Hons) (Food Science)

Abstract This work investigates the kinetics of the emulsion polymerization of vinyl acetate. Several aspects of this system have been clarified, including the induced decomposition of persulfate, retardation by oxygen and entry by, and analysis of, the aqueous phase oligomeric radicals. It has been shown that the retardation period observed in the emulsion polymerization of VAc can be explained by the effect of traces of oxygen (< 10-6 M) on the entry efficiency of the initiator-derived aqueous-phase oligomeric radicals. Comparison of rates of polymerization in V and persulfate -initiated polymerizations together with electrospray mass spectrometry of aqueous phase oligomers, has shown that the mechanism for the induced decomposition of persulfate by vinyl acetate is chain transfer to initiator from aqueous-phase oligomeric radicals. A value has been determined for the rate coefficient for transfer to initiator, by fitting literature data to a model based on this mechanism. The reported independence of the rate of polymerization from the monomer concentration in the emulsion polymerization of vinyl acetate has been investigated. Possible explanations for this behaviour have been proposed and tested in this work, by measuring radical-loss rates directly with y-relaxation techniques. Although the Y relaxations were found to be affected by experimental artefacts, it has been demonstrated that rapid exit is not responsible for the high radical-loss rates in this system. The major artefact identified in the y relaxations was the significant effect of relatively small exotherms on relaxation behaviour, Methodologies were developed for correcting affected data and for avoiding exotherms under certain conditions. Arrhenius parameters were determined for the rate coefficient for chain transfer to monomer using the In^M method, which utilises the whole MWD. This section of the work is incomplete, for reasons detailed in chapter 5. However, as a preliminary indication it was found that the frequency factor was 106.38 M-1 s-1 and the activation energy was 38.8 kJ mol-1.

Photobiological hydrogen production from organic acids occurs in the presence of light and under anaerobic conditions. Stable and optimized operation of the photobioreactors is the most challenging task in the photofermentation process. The main aim of this study was to achieve in long term, a stable and high hydrogen production on acetate, using the photosynthetic bacteria Rhodobacter capsulatus in continuous panel photobioreactors. Rhodobacter capsulatus (DSM 1710), heat adapted Rhodobacter capsulatus (DSM 1710) and Rhodobacter capsulatus YO3 (Hup-), a mutant strain, were tested in outdoor conditions, under natural sunlight between September-December, 2008 in Ankara, Turkey. Defined culture medium containing acetate (40 mM) and glutamate (2 mM) and a dilution rate of 0.8 l/ day were used. Steady hydrogen production (0.4 mmol H2/lc.h) was obtained using the Rhodobacter capsulatus YO3 (Hup-) mutant strain that was continuously operated for 69 days, but the cell concentration could not be kept at a steady value. Further efforts were focused on achieving stable biomass concentration by optimizing the feed composition. Stable biomass (0.40 gdcw/lc) and high hydrogen productivity (0.8 mmol H2/lc.h) were achieved using feed media containing 40 mM acetate and 4 mM glutamate with a 10% (v/v) feed rate. Moreover, the EU project HYVOLUTION aims to combine dark fermentation and photofermentation process for the conversion of biomass to hydrogen. Effluents from the dark fementation contain high amount of ammonium, which inhibits phototrophic hydrogen production. After treatment it has been concluded that G&ouml / rdes clinoptilolite zeolite effectively removes ammonium ion from the dark fermenter effluent of molasses.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1940. / Includes bibliographical references (p. 96-97).

Thesis (M. Phil.)--University of Hong Kong, 1987.

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.