DEVELOPMENT OF NEW CHROMATOGRAPHIC METHODS FOR THE CHARACTERIZATION OF SURFACES, COLLOIDAL PARTICLES AND MACROMOLECULES

DEVELOPED NEW METHODOLOGIES OF FIELD-FLOW-FRACTIONATION(FFF) FOR THE SEPARATION AND CHARACTERERIZATION OF COLLOIDAL PARTICLES AND MACROMOLECULES. THIS DEVELOPMENT COMPRISED: 1. METHODOLOGIES FOR THE SIMULTANEUS DETERMINATION OF PARTICLE SIZE AND DENSITY IN POLYDISPERSE COLLOIDAL SAMPLES. THIS CAN BE DONE BYAWETHODOLOGY BASED ON THE VARIATION OF THE CARRIER SOLUTION DENSITY USING VARIOUS AQUEOUS GLYCEROL SOLUTIONS HAVING DIFFERENT CONCENTRATIONS. 2. THE REVERSIBILITY OF ADHESION OF COLLOIDAL PARTICLES ON THE CHANNEL WALL IN SFFF THROUGHT THE VARIATION OF THE IONIC STRENGTH OF THE CARRIER SOLUTION, HAS BEEN THE BASIS PF A NEW METHOD, FOR THE SEPARATION AND CHARACTERIZATION OF COLLOIDAL MATERIAL. THIS NEW METHOD, CALLED "POTENTIAL BARRIER FIELD-FLOW FRACTIONATION", WAS APPLIED FOR THE SEPARATION OF HAEMATITE AND TITANIUM DIOXIDE SPHERICAL COLLOIDAL PARTICLES WITH DIFFERENT SIZES. 3. A NEW METHODOLOGY FOR THE CONCENTRATION AND PARTICLE SIZE ANALYSIS OF DILUTE POLYDISPERSE COLLOIDAL SAMPLES IS PRESENTED. THE NEW METHODOLOGY OF POTENTIAL BARRIER FFF WAS SUCCESSFULLY APPLIED FOR THE CONCENTRATION OF DILUTE MONODISPERSE COLLOIDAL SAMPLES OF HAEMATITE. (ABSTRACT TRUNCATED

Kinetic Study of Fig Syrup Fermentation by Genetically Modified <i>Saccharomyces cerevisiae</i> Yeast Strains: A Physicochemical Approach to the Yeast Strain Life Cycle

Reversed-flow gas chromatography (R.F.G.C.) was employed to assess the impact of genetic modification on Saccharomyces cerevisiae yeast strains during the process of alcoholic fermentation, utilizing fig syrup. Multiple fermentations were carried out at various temperatures to evaluate the influence of genetic modifications on yeast strain efficiency. The study involved a wild-type yeast strain, W303, as a control and two genetically modified strains, W_M4_533 and W_M4_558, sharing the same genetic background as the wild type. Notably, the genetic modifications in the Msn4p transcription factor involved the substitution of serine residues with alanine at positions 533 and 558, resulting in the development of psychrophilic or ethanol-resistant strains. Utilizing the R.F.G.C. method enabled the differentiation of the duration of alcoholic fermentation phases, providing insights correlated to the yeast cell life cycle. The values of rate constants (k) for each phase, conducted with both wild-type and genetically modified cells using RFGC, aligned with the existing literature. Additionally, the calculation of activation energies for distinct phases revealed lower values for genetically modified strains compared to wild-type strains. This decrease in activation energies suggests enhanced efficiency in the alcoholic fermentation process for the genetically modified strains

Fermentation Efficiency of Genetically Modified Yeasts in Grapes Must

Winemaking is a stressful procedure for yeast cells. The presence of high levels of carbohydrates at the beginning of the fermentation and the subsequent increase of ethanol levels alongside with other environmental factors force the cell to undergo a continuous adaptation process. Ideally, yeast strains should be able to adapt to this changing environment fast and they must be able to ferment at low temperatures with the highest possible fermentation rates. Additionally, the balanced utilization of glucose and fructose—the two major hexoses in grapes—is also important as any residual fructose may confers unwanted sweetness. As proteins, Msn2/4 are known to play pivotal roles in cell stress response, the question that arise regards the differentially cell response driven by specific point mutations in these two proteins, and the subsequent effects on alcoholic fermentation. Four different mutants in which serine residues have been replaced by alanine are studied in this paper. Our results indicate that substitution at position 533 of Msn4 protein (W_M4_533) significantly increases the fermentation rate even at low temperatures (12 °C), by lowering the fermentation’s activation energy. Similar results but to a lesser extent were obtained by the S582A substitution in Msn2 protein. In addition, W_M4_533 seems to have a more balanced utilization of must hexoses. From the present work it is concluded that genetic modification Msn2/4 represents a promising procedure for shortening the fermentation time, even at low temperatures, which in many cases constitutes an important technological requirement