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 Four different mutants in which serine residues have been replaced by alanine are studied in this paper.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.

Reversed-Flow Gas Chromatography as a Tool for Studying the Interaction between Aroma Compounds and Starch.

The versatile technique of reversed-flow gas chromatography was introduced to calculate physicochemical quantities for the interaction between aroma compounds and starch. Adsorption, adsorption/desorption, and surface reaction rate constants as well as surface diffusion coefficients for the vapors of aroma compounds over the different starch surfaces were calculated in the temperature range of 303.15-333.15 K. Enthalpies of adsorption between -45.5 and -109.0 kJ mol-1 and enthalpies of physicochemical interaction between 6.8 and 47.4 kJ mol-1 were also calculated for all the systems studied. From the obtained results, it is concluded that the interaction forces between aroma compounds and starch correspond to weak energy bonds such as hydrogen bonds and dipole-dipole interactions. For all the systems studied, except for the system heptanal/potato, physical sorption of aroma compounds on starch granules was indicated according to the calculated activation energies.

Study of the influence of surfactants on the activity coefficients and mass transfer coefficients of methanol in aqueous mixtures by reversed-flow gas chromatography.

This work focuses on the influences of surfactants on the activity coefficients, γ, of methanol in binary mixtures with water, as well as on the mass transfer coefficients, kc, for the evaporation of methanol, which is a ubiquitous component in the troposphere, from mixtures of methanol with water at various surfactant's and methanol's concentrations. The technique used is the Reversed-Flow Gas Chromatography (R.F.G.C.), a version of Inverse Gas Chromatography, which allows determining both parameters by performing only one experiment for the kc parameter and two experiments for the γ parameter. The kc and γ values decrease in the presence of the three surfactants used (CTAB, SDS, TRITON X-100) at all methanol's and surfactant's concentrations. The decrease in the methanol's molar fraction, at constant number of surfactant films leads to a decrease in the kc and γ values, while the decrease in the surfactant's concentration, at constant methanol's molar fraction leads to an increase in both the kc and γ parameters. Mass transfer coefficients for the evaporation of methanol at the surfactant films, are also calculated which are approximately between 4 and 5 orders of magnitude larger than the corresponding mass transfer coefficients at the liquid films. Finally, thicknesses of the boundary layer of methanol in the mixtures of methanol with water were determined. The quantities found are compared with those given in the literature or calculated theoretically using various empirical equations. The precision of the R.F.G.C. method for measuring γ and kc parameters is approximately high (94.3-98.0%), showing that R.F.G.C. can be used with success not only for the thermodynamic study of solutions, but also for the interphase transport.

Kinetic study of aggregation of milk protein and/or surfactant-stabilized oil-in-water emulsions by sedimentation field-flow fractionation.

Milk proteins are able to facilitate the formation and stabilization of oil droplets in food emulsions. This study employed Sedimentation Field-Flow Fractionation (SdFFF) to monitor changes in particle size distribution of freshly prepared emulsions with varying weight contributions of sodium caseinate (SC) and whey protein concentrate (WPC). The effect of the addition of Tween 80 (T) on the initial droplet size was also investigated. The results indicated that emulsifying ability follows the order Tween 80>WPC>SC, with corresponding weight average droplet diameter of 0.319, 0.487 and 0.531µm respectively, when each of the above emulsifiers was used solely. The stability of sodium caseinate emulsions was studied at 30.5 and 80.0°C by measuring the particle size distribution for a period of 70h. Emulsions withstood the temperatures and exhibited an initial increase in particle size distribution caused by heat-induced droplet aggregation, followed by a decrease to approximately the initial droplet size. The rate of droplet aggregation depends on the severity of thermal processing, as revealed by the kinetics of particle aggregation during aging at different temperatures. Comparison of the experimental rate constants found from SdFFF, with those determined theoretically gives invaluable information about the oil droplet stability and the aggregation mechanism. Based on the proposed mechanistic scheme various physicochemical quantities, which are very important in explaining the stability of oil-in-water emulsions, were determined. Finally, the advantages of SdFFF in studying the aggregation of the oil-in-water droplets, in comparison with other methods used for the same purpose, are discussed.

Estimation of the Hamaker constants by sedimentation field-flow fractionation.

van der Waals forces are one of several forces that control the adhesion between two materials. These forces are important to quantify in adhesion studies because they are always present and are always attractive. The major problem in calculating the van der Waals interaction between colloidal particles is that of evaluating the Hamaker constant. Hence, an accurately determined Hamaker constant for a given material is needed when interfacial phenomena such as adhesion are discussed in terms of the total potential energy between a particle and a substrate. In this paper, a new simple and accurate methodology for the estimation of the Hamaker constant is introduced. The results are in good agreement with those values found in literature.

Time distribution of adsorption entropy of gases on heterogeneous surfaces by reversed-flow gas chromatography.

The reversed-flow gas chromatography (RF-GC) technique has been applied to measure the adsorption entropy over time, when gaseous pentane is adsorbed on the surface of two solids (gamma-alumina and a silica supported rhodium catalyst) at 393.15 and 413.15K, respectively. Utilizing experimental chromatographic data, this novel methodology also permits the simultaneous measurement of the local adsorption energy, epsilon, local equilibrium adsorbed concentration, c(s)(*), and local adsorption isotherm, theta(p, T, epsilon) in a time resolved way. In contrast with other inverse gas chromatographic methods, which determine the standard entropy at zero surface coverage, the present method operates over a wide range of surface coverage taking into account not only the adsorbate-adsorbent interaction, but also the adsorbate-adsorbate interaction. One of the most interesting observations of the present work is the fact that the interaction of n-pentane is spontaneous on the Rh/SiO(2) catalyst for a very short time interval compared to that on gamma-Al(2)O(3). This can explain the different kinetic behavior of each particular gas-solid system, and it can be attributed to the fact that large amounts of n-C(5)H(12) are present on the active sites of the Rh/SiO(2) catalyst compared to those on gamma-Al(2)O(3), as the local equilibrium adsorbed concentration values, c(s)(*), indicate.

Estimation of the particle-wall interaction energy in sedimentation field flow fractionation.

A new sedimentation field flow fractionation (SdFFF) method is presented for the estimation of the total potential energy of interaction between colloidal particles and the channel wall. The method is based on the variation of the mean cloud thickness in SdFFF due to the variation of the suspension's ionic strength. It requires only two SdFFF experiments at two different ionic strengths and at a constant acceleration field. The found values are compatible with those calculated from the various forms of equations of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory.

New gas chromatographic instrumentation for studying the action of sulfur dioxide on marbles.

Reversed-flow gas chromatography, which is a sub-technique of inverse gas chromatography, is an experimental arrangement simulating a simple model for the action of air pollutants on buildings and monuments, in laboratory scale. By using a commercial gas chromatograph and an appropriate mathematical analysis, kinetic parameters such as rate constants for adsorption k1, adsorption/desorption kR and surface reaction k2, as well as surface diffusion coefficients Dgamma, deposition velocities Vd and reaction probabilities gamma of SO2 on marble surfaces at different temperatures (303.15-353.15 K) in the presence or in the absence of protective materials (an acrylic copolymer, Paraloid B-72 or a siloxane, CTS Silo 111) were calculated. From the above mentioned physicochemical quantities the ability of the examined materials to minimize the dry deposition of SO2 on marble is carrying out and a possible mechanism for the interaction between SO2 and Paraloid B-72 was suggested. Both materials (CTS SILO 111 and Paraloid B-72) are good enough for protecting marble against SO2 at low temperatures (303.15-323.15), while at high temperatures (333.15-353.15), siloxane seems to protect marble better than acrylic copolymer.

Kinetic study of cell proliferation of Saccharomyces cerevisiae strains by sedimentation/steric field flow fractionation in situ.

The technique of Sedimentation/Steric Field Flow Fractionation (Sd/StFFF) is applied to the kinetic study of cells proliferation of Saccharomyces cerevisiae strains. The experimental parameter varied is the time from the preparation of the yeast sample dispersion in the culture medium. The determination of the size and mass distributions of the yeast cells is combined with the growth of the yeast cells and their life cycle. The experimental results are compared with those obtained by scanning electron microscopy (SEM) and those found in the literature. Useful conclusions concerning the budding and the fission of these yeast cells were extracted.