No description available.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Plant Science, 2000. / Bibliography : leaves 74-92.

1. The inhibitory effect of glucosone on yeast fermentation was shown to the specific for the D-isomer, and exerted at some point before the breakdown of fructose-1:6-diphosphate. 2. The results of the fermentation experiments are analysed, kinetically, and glucosone shown to be a pseudo-irreversible inhibitor, of the type described by Ackermann and Potter (1949). It is shown that the effects produced by glucosone in animals can be correlated vd.th this finding. 3. The osone is shown to be phosphorylated by ATP in the presence of hexokinase. 4. It is suggested that the inhibitory effect produced by glucosone on yeast fermentation, is due to the slow dissociation of a glucosone phosphate from the hexokinase molecule. 5. The effect of hexokinase on a number of glucose analogues is reported, and indications are given of the high degree of specificity exhibited by the enzyme. 6. Methods are described for the preparation of an actively fermenting acetone-dried extract, and a maceration juice, from 'bakers' yeast. The preparation and some properties of cold-treated bakers' yeast are also described. 7. A method is described for the separation of the substrates .and products of the hexokinase reaction, on paper chromatograms.

No description available.

Experiments have been conducted to identify the fouling mechanism during the crossflow filtration of a model yeast fermentation broth of Vinyl Acetate particles suspended in a Bovine Serum Albumin (BSA) solution. These have been conducted with filter modules, to obtain quantitative data for the rate and the extent of flux decline due to membrane fouling, and with filter coupons, to obtain quantitative data for the build up of the fouling layer with each individual system and the mixed system. The data from the individual systems have been analysed and then used to determine their fouling mechanisms; this information has been used to predict the fouling mechanism for the mixed system. Finally, this prediction has been compared to the actual fouling mechanism determined by analysis of the mixed system data. For the model particulate suspension, the fouling was due to the build up of a cake layer, as with dead end filtration; however, fouling was limited by membrane scouring. For the model macromolecular solution, a four part fouling mechanism was identified: initially aggregates formed within the pores; the concentration at the membrane surface increased until protein came out of solution as strands; the strands disappeared causing increased aggregation in the pores; finally, a mesh formed on the membrane surface. For the mixed system, fouling was due to the formation of a particle cake on the membrane surface with protein aggregates forming in the pores. The fouling kinetics could be predicted by considering the results from the individual systems; however, the fouling mechanism could not be predicted without using visualisation experiments due to the interactions between the particles and the macromolecules.

Thesis--Université de Genève. / Bibliography: p. 46-47.

Alternatives to antibiotic growth promoters have been widely exploited due to concerns about antimicrobial resistance. These feed additives improve growth, in part, by modulating intestinal microbiota. However, their impact on male reproductive performance is not well elucidated. Therefore, the objective of this study was to evaluate the impacts of a yeast fermentation product (YP) and Bacillus subtilis on rooster semen quality and microbiota. Dietary supplementation of YP linearly increased the concentration of yeast and bacteria in semen, whereas it linearly decreased sperm motility, suggesting that bacteria attached to yeast were excreted from the gut, contaminated semen at the cloaca and then decreased sperm movement. However, direct in vitro exposure of semen or dietary supplementation with B. subtilis did not affect semen quality or seminal concentration of this bacterium, likely because Bacillus naturally occur in semen. In conclusion, unlike B. subtilis, dietary YP can alter semen quality by altering semen microbiota.

In the large-scale production of <i>Saccharomyces cerevisiae</i> (baker's yeast), oxygen transfer, which is one of the major limiting factors, is improved by using high agitation rates. However, high agitation rates subject the microorganisms to high shear stress and caused high power consumption. A microbubble dispersion (MBD) method was investigated to improve oxygen transfer at low agitation rates and thus reduce power consumption and shear stress on the microorganisms. The experiments were conducted at the 1-liter level and subsequently scaled-up to 50-liters using a constant volumetric oxygen transfer coefficient (<i>k_La</i>) method for scaling. In comparison to a conventional air-sparged fermentation, the MBD method considerably improved the cell mass yield, growth rate and power consumption in the 50-liter fermentor. Cell mass production in the MBD system at agitation rate of 150 rpm was about the same as those obtained for a conventional air-sparged system agitatid at 500 rpm. Power consumption in the conventional air-sparged system was three-fold that required for the same biomass yield in the MBD system. However, at the 1-liter scale, the MBD system did not show any significant advantage over the air-sparged system because of the high power consumption. / Master of Science

L'étude et le développement des procédés de fabrication de levures immobilisées en vue de la réalisation de fermentations de vins a débuté au milieu des années 80. Malgré les bénéfices potentiels que cette technologie pouvait apporter pour le secteur œnologique, peu de procédés d'immobilisation ont réussi à dépasser l'échelle laboratoire ou pilote et ceux qui sont arrivés à l'échelle industrielle n'ont pas eu le succès désiré pour des questions d'ordre technique ou économique. Le premier objectif de ce travail concerne la mise au point du procédé industriel en insistant sur les aspects les plus sensibles, et qui comme tels ont exigé des études complémentaires. Le deuxième objectif de ce travail vise à caractériser du point de vue cinétique et lorsque possible sensoriel, les fermentations avec les levures immobilisées pour la production de vins effervescents et pour la désacidification biologique de moûts. Le troisième et dernier objectif de ce travail consiste à évaluer l'utilisation de levures immobilisées pour la réalisation de la fermentation alcoolique en continu de moût. Pour cela on a fait appel à des fermenteurs continus à lit fixe et à lit fluidisé. / The study and development of yeast immobilization processes for wine fermentations started in the mid 80’s. Even though this technology could be of great benefit for the oenological sector very few process left the laboratory or pilot scale and those which arrived to industrial scale didn’t have the ambitioned success due to technical or economical constraints. The first goal of this work was to develop an industrial process for yeast immobilisation with emphasis on the most sensitive aspects which required further studies. The second objective of this work was to characterise the fermentation kinetics of immobilised yeasts cells during the production sparkling wines and during the deacidification of grape must. Whenever possible the wines produced were also characterised from a sensorial point of view. The third and last goal was to evaluate the use of immobilised yeast cells for continuous fermentation of grape must. For that we have used continuous fixed bed and fluidized bed fermenters.

Through a full factorial design experiment, the effects of time between worts, wort aeration and yeast dosage in production of a pale lager beer were examined in the beer process at Spendrups Bryggeri AB. The aim was to learn how different parameters may affect the yeast fermentation performance during beer production. Response variables used were the concentrations of ethyl acetate and isoamyl acetate, free amino nitrogen (FAN) degradation and change in extract. A statistical analysis showed that the concentration of ethyl acetate is dependent on yeast dosage and the interaction between time between worts and aeration while the isoamyl acetate concentration is dependent on yeast dosage and time between worts. No parameters are statistically significant for FAN degradation while the change in extract is dependent on the yeast dosage. Due to botched runs, mostly because of aeration problems, it was not possible to verify theoretical parameter values and responses. Since the aeration was not properly performed, the management of the aeration control should be further investigated. Ester analysis and analysis of FAN were performed as worts entered and exited horizontal fermentation tanks. An additional analysis of ester content was also performed as the early stage beer was transferred into lagering tanks. Cell viability as well as extract, pH and tank temperature was measured daily to verify the state of fermentation. Statistical calculations showed that when using NucleoCounter YC-100, there is no significant difference between analysis made of samples homogenized by a magnetic stirrer and samples shaken by hand.