The wine yeast Saccharomyces cerevisiae experiences a range of stress conditions during wine fermentation. These stresses include osmotic stress, hypoxia, nutrient starvation, cold stress and increasing ethanol stress as fermentable sugars are converted to ethanol. These various stresses affect the functionality of the plasma membrane, cell wall and subsequently the yeast’s efficiency during fermentation. Etp1, a poorly characterized protein has been shown to have several different fermentation related phenotypes; it is needed for the turnover of the hexose transporter Hxt3 upon a shift from glucose to ethanol, and the transcriptional activation of the stress response genes HSP12 and HSP26 under ethanol stress. The molecular function of Etp1 during fermentation is not understood. This research aims to understand the molecular mechanism of Etp1 function and its involvement in Chardonnay fermentation using the S. cerevisiae M2 wine yeast strain. / OMAFRA, Genome Canada

No description available.

No abstract available. / Thesis (M. Sc.)-University of Durban-Westville, 1994.

This study was aimed at investigating the potential of lactic acid fermentation in reducing myco toxin concentration in maize meal products. Maize meal was spiked separately with aflatoxin Bi, fumonism Bi, and zearalenone, and fermented for four days. During this period the concentration of each toxin and the pH of the fermented maize meal were monitored. There was a significant (p= 0.000) decrease in the concentration of all the mycotoxins, with a percentage reduction of 55-69 by the third day and 68-75 by the fourth day, respectively. Commercial amahewu samples were also screened for the presence of these three mycotoxins, and the results indicated that the samples were not contaminated with detectable levels of these toxins. An attempt was made to characterise the metabolic derivatives (by-products) of each mycotoxin following lactic acid maize meal fermentation. To achieve this maize meal samples were separately spiked with each of mycotoxin, fermented for four days and screened for specific mycotoxin derivatives (by-products) using GC/MS, HPLC and relevant standards (i.e. partially hydrolysed fumonisin Bi, aflatoxin B2a, a- and Pzearalenol). None of the targeted derivatives could be detected in the fermented maize meal samples. The potential cytotoxicity of the mycotoxin-spiked fermented samples was investigated using an SNO cell line. The fermented toxin-spiked maize meal samples with a starter culture were comparatively less toxic (29 - 36%) to SNO oesophageal cells than samples spiked with toxin without a starter culture (24 - 30%). However, this observed difference was not statistically significant (p = 0.295 - 0.681). Furthermore, cells that were only inoculated with the cell culture medium had significantly (p = 0.000) high percentage cell viability. This study indicates that it is possible to significantly reduce the concentration of mycotoxins using lactic acid maize fermentation to trace levels. However, such a reduction will not significantly alter the possible chronic toxic effects of such toxins in the diet, particularly a maize based diet containing poor quality protein. The trace amounts of these toxins in fermented and unfermented maize meal should continue to be a cause for concern. / Thesis (M.Med.Sc.)-University of Natal, Durban, 2003.

The relationship between the cellulolytic Clostridium termitidis and the electrogenic Geobacter sulfurreducens was evaluated in terms of co-culture sustainability and hydrogen production. Batch co-culture experiments in triplicate balch tubes were conducted using cellobiose as the sole carbon source and fumarate as a terminal electron acceptor. Despite high initial concentrations of acetate, no formate and very low H2 concentrations were detected, supporting the hypothesis that a syntrophic association exists between both bacteria. Co-culture growth characterization experiments were repeated in three microbial electrolysis cells and cellobiose as the sole carbon source. Initially, 9.7 mol-H2 mol-1-glucose was produced. However, a sustainable co-culture could not be maintained despite efforts to reduce reactor temperature and triple the medium’s buffering capacity. Strategies to achieve a sustainable co-culture are to minimize the carbon flux through C. termitidis by using complex substrates, maintain neutral operating conditions, and introduce acetogenic bacteria to control the flux of metabolic intermediates.

No description available.

The production of bio-ethanol from lignocellulosic material requires a more efficient process to be feasible and compete with products from fossil fuels. There is a need to rapidly and nondestructively be able to determine key components during fermentation. Raman spectroscopy is a technique, which can be used to monitor the fermentation process in real-time and provide information about key components which can be accessed immediately, thus facilitating process control. A continuous system with membrane cell recycling was set up and fermentations were performed using Saccharomyces cerevisiae ATCC 96581. Fermentations were performed to test for optimal dilution rates and operating times, the effect of different sugar concentrations in the media feed, and which position in the system was optimal for Raman data collection. Raman data and aliquot samples for HPLC validation were continuously collected throughout the fermentations. Raman data was analysed with PLS models to obtain component concentrations, for which RMSE was calculated in order to compare to HPLC validation set. Fermentations were performed with synthetic glucose media as well as with poplar hydrolysate. It was shown that the continuous system with membrane cell recycling could achieve a glucose-to-ethanol conversion of between 75-100%. The process could be sufficiently monitored by Raman spectroscopy, and predicted concentrations were within the range of the validation set in most cases. However, the error of prediction varied between the different fermentations.

Many antibiotics are produced as secondary metabolites of Streptomyces species. Commercial production of an antibiotic involves the optimization of environmental parameters, genetic makeup, and medium. Selection of ingredients for both inoculum (seed) and fermentation (production) media must provide for economic production, and easy downstream processing of the compound. Antibiotics are produced as secondary shunt metabolites and represent products that are not essential for primary metabolism of the cell; therefore conditions for their optimal expression may or may not be associated with good growth of the organism. Response Surface Methodology (RSM) is a collection of statistically designed experiments and analyses that directs the investigation of many factors and their interactions. This approach minimizes the number of trials required to identify critical factors and possible synergism between factors. In this research, an antifungal antibiotic produced by an unknown streptomycete collected from soil, was isolated, characterized and identified as cycloheximide. RSM was then used toformulate both a seed and production medium that optimizes cycloheximide biosynethesis. For the seed medium, RSM was used in a three step process: i) full factorial categorical screen of many factors, ii) Plackett-Burman two-level screen of promising factors, and iii) orthogonal central composite design of critical factors. Optimal 24 hour packed cell volume was found with a seed medium containing (g/L): 6.6g soluble starch, 23.4g yeast extract, and Mg K2HPO4. Additionally, the effects of inoculum age and passage on resulting cycloheximide production were studied. It was found that the negative effects of increasing inoculum age and passages on cycloheximide production could be mediated by the composition of the seed medium. For the production medium, RSM analysis of 29 ingredients suggests that an optimal production medium for cycloheximide biosynthesis should contain a combination of starch (40 g/L), corn gluten (17.8 g/L), MgSO4.7H2O (1.16 g/L), and NaCl (6.38 g/L). This final production medium resulted in a cycloheximide titer of 943 µg/ml, a 6-fold improvement in antibiotic production. / Department of Biology

Access to abstract permanently restricted to Ball State community only. / Access to thesis permanently restricted to Ball State community only. / Department of Biology

Ethanol production through biomass fermentation is one of the major technologies available to produce liquid fuel from renewable energy sources. A major problem associated with the production of ethanol through fermentation remains the inhibition of the yeast Saccharomyces cerevisiae by the produced ethanol. Currently high water dilution rates are used to keep the ethanol concentrations in the fermentation broth at low concentrations, resulting in low yields and increased downstream processing to remove the excess water. Yeast strains that have a high tolerance for ethanol have been isolated but the time and cost associated with doing so poses a challenge. The fermentation process can be combined with pervaporation, thereby continuously removing ethanol while it is being formed. In this study a mathematical model for ethanol fermentation with yeast, Saccharomyces cerevisiae, coupled with pervaporation was developed. The fermentation of glucose was optimised in the first part of the study and experimental data were obtained to find a kinetic model for fermentation. It was found that an optimum ethanol yield can be obtained with an initial glucose concentration of 15wt%, a yeast concentration of 10 g.L–1, and a pH between 3.5 and 6. The maximum ethanol yield obtained in this study was 0.441g.g–1 (86% of the theoretical maximum) using 15wt% glucose, 10g/L yeast and a pH of 3.5. Two kinetic models for fermentation were developed based on the Monod model. The substrate–limiting model, predicted fermentation very accurately when the initial glucose concentration was below 20wt%. The second model, the substrate–inhibition model, predicted fermentation very well when high initial glucose concentrations were used but at low glucose concentrations, the substrate–limiting model was more accurate. The parameters for both models were determined by non–linear regression using the simplex optimisation method combined with the Runge–Kutta method. The PERVAP®4060 membrane was identified as a suitable membrane in this study. The effect of the ethanol content in the feed as well as the influence of the glucose content was investigated. The total pervaporation flux varied with ethanol content of the feed and the highest total flux of 0.853 kg/m2h was obtained at a feed with 20wt% ethanol. The addition of glucose had almost no effect on the ethanol flux but it lowered the water flux, thereby increasing the enrichment factor of the membrane. The mass transport through the PERVAP®4060 membrane was modelled using the solution–diffusion model and Greenlaw’s model for diffusion coefficients was used. The limiting diffusion coefficient (Di0) and plasticisation coefficients (Bij) were determined by using the Nelder–Mead simplex optimisation method. The theoretical values predicted with the model showed good agreement with the measured experimental values with R2 values above 0.998. In the third part of this investigation, the kinetic model developed for fermentation was combined with the transport model developed for pervaporation. The combined kinetic model was compared to experimental data and it was found that it could accurately predict fermentation when coupled with pervaporation. This model can be used to describe and better understand the process when fermentation is coupled with pervaporation. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.