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PubMedDate not supplied

[Characteristics of structural changes in the internal organs of animals after administration of dried yeast].

Morphofunctional analysis of the state of internal organs was made in rats which received varying amounts of mushroom powder. It has been established that the new product induces development of endovasculitis, dystrophy and lympho-histiocytic infiltrates of parenchymatous organs. The data obtained have evidenced the development of delayed allergic reactions to mushroom powder. A conclusion has been made on the necessity of its limited inclusion into food ration.

Animal Feed↗
PubMedDate not supplied

Glass transition temperatures and fermentative activity of heat-treated commercial active dry yeasts.

Differential scanning calorimetry thermograms of various samples of commercial instant active dry yeasts revealed a clear glass transition typical of amorphous carbohydrates and sugars. The resulting glass transition temperatures were found to decrease with increasing moisture content. The observed glass curve was similar to that of pure trehalose, which is known to accumulate in large amounts in baker's yeast. The effect of heat treatment at various temperatures on the fermentative activity (as measured by the metabolic production of CO(2)) of dry yeast was studied. First-order plots were obtained representing the loss of fermentative activity as a function of heating time at the various temperatures assayed. Significant losses of fermentative activity were observed in vitrified yeast samples. The dependence of rate constants with temperature was found to follow Arrhenius behavior. The relationship between the loss of fermentative activity and glass transition was not verified, and the glass transition was not reflected on the temperature dependence of fermentative activity loss.

Biotechnology↗
PubMed2005

Formation of micella containing solubilized sterols during rehydration of active dry yeasts improves their fermenting capacity.

During their rehydration in aqueous media, active dry yeasts (ADY) may be supplemented with inactive yeasts, yeast derivatives, or other optional complementary nutrients to improve their fermentation capacity. We found that yeast sterols solubilized in situ during ADY rehydration were particularly efficient for stimulating the fermenting capacity of ADY. Spontaneous solubilization of sterols during rehydration occurred by the formation of micelles by membrane phospholipids and specific cell wall polysaccharides and sterols, both compounds being provided by inactive dry yeasts (IDY). These micelles contained a specific distribution of the initial sterols from the inactive yeasts. Above a concentration of 100 mg L(-1) in the rehydration medium, these micelles acted as emulsifiers. Their critical micellar concentration (cmc) was found to be about 4 g L(-1). During rehydration, purified micelles, at a concentration near the cmc, were able to interact quickly with yeast cell membranes by modifying the yeast plasma membrane order [monitored by steady-state fluorescence anisotropy of 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene-p-toluenesulfonate (TMA-DPH) probe] and by increasing the sterol contents of ADY. Such an enrichment of ADY by very low concentrations of solubilized sterols was very efficient for the completion of fermentations. This is useful when musts are limited in available phytosterols or when micro-oxygenation is not desirable during fermentation.

Cell Wall↗
PubMed2003

Comparison of components released by fermented or active dried yeasts after aging on lees in a model wine.

Comparison of different components released during autolysis with fermented or active dried yeast, which has never been reported previously, is related in this paper. Three autolysates were elaborated with Saccharomyces cerevisiae in a model wine (pH 3.5) at 30 or 18 degrees C. Composition of the autolysate appears to depend on both the growth medium and the physiological state of the yeast. The autolysate obtained from active dried yeast presents a higher total nitrogen concentration (a factor of 1.5-1.9 for the fermented yeast autolysate), a greater proportion of free amino acids (42 vs 16-25%), the lowest proportion of oligopeptides (25 vs 31-37%) and polypeptides (27 vs 45-34%), and an absence of nucleosides. Distribution of amino acids in peptides and proteins is relatively homogeneous in the autolysates but shows significant differences in free amino acids. Parietal macromolecules (mannoproteins and glucans) are present in greater quantities in autolysates elaborated from fermented yeast. The influence of the different fractions of these autolysates (<0.5, 0.5-1, 1-10, and >10 kDa) on bacterial growth has been investigated.

Amino Acids↗
PubMed1992

Molecular monitoring of wine fermentations conducted by active dry yeast strains.

A simple and rapid method of yeast strain characterization based on mitochondrial DNA restriction analysis was applied to the control of wine fermentations conducted by active dry yeast strains. This molecular approach allows us to understand several important aspects of this process, such as the role of the active dry yeast strain and that of the natural Saccharomyces cerevisiae flora during vinification. In this paper, we demonstrate that the inoculated strain is really responsible for the fermentation but does not suppress significant development of natural strains during the first stages. During this early period, natural strains could have important effects on wine flavor.

Journal Article↗
PubMed2006

Classical and molecular analyses to characterize commercial dry yeasts used in wine fermentations.

AIMS: The aim of the work was to apply PCR-temperature gradient gel electrophoresis (PCR-TGGE) and restriction enzyme analysis (RE) assays to identify commercially available starters of Saccharomyces cerevisiae sensu stricto complex. METHODS AND RESULTS: To characterize an analysed pool of 62 active dry yeasts of different brands used in wine fermentation practices, classical microbiological tests were also performed as well as evaluation of contamination with lactic acid bacteria and non-Saccharomyces yeasts. PCR-TGGE and RE were used in order to provide fast and reliable methods to identify and differentiate enological yeasts. Proposed molecular methods enabled to identify particular strains within 36 h after colony isolation and directly from dry yeast suspension. CONCLUSIONS: The methods are highly recommended to obtain reliable results on yeast strain differentiation in a significantly shorter time if compared to classical fermentation tests. SIGNIFICANCE AND IMPACT OF THE STUDY: The obtaining of yeast strain differentiation in a short time and without plating is a good tool for a rapid discrimination among enological strains used as starters in enological practices.

Colony Count, Microbial↗
PubMed2002

Determination of mineral content of active dry yeast used in pharmaceutical formulations.

The efficiency of seven common methods of digestion of active dry yeast (ADY), which is used in anticariogenic dental formulations, was evaluated for the analytical determination of Fe, Zn, Ca, Mg, Na and K. Four wet-acid digestion and three dry ashing methods are compared in consideration of their estimated reproducibility and metal concentrations obtained. HNO(3), HNO(3)+HCl, HNO(3)+H(2)SO(4) and HNO(3)+HClO(4) were applied for wet digestion of the samples in medium temperatures, while dry ashing at higher temperature with Mg(NO(3))(2) or SrCl(2) as ashing aid agents, were the alternative methods. The final solutions were subsequently analyzed for Fe, Zn, Ca and Mg by flame atomic absorption spectroscopy (FAAS) and for Na and K by atomic emission spectroscopy (AES). Two multivariate statistical methodologies, Analysis of variance (ANOVA) and the Kruskal-Wallis test were applied for the interpretation of the results. Seven additional statistical tests (least-significant difference, Bonferoni, Duncan multiple range, Student-Newman-Keuls, Tuckey significant difference, Tuckey b and Scheffe) were used and proved useful to estimate which of the decomposition methods are outliers. The ideographic approach enabled the comparison of the methods in terms of complexity and difficulty of their steps. Zn and Mg could be reliably determined by any one of the tested methods, while for the other elements, the most powerful method was found and the obtained recoveries were found (>95%).

Data Interpretation, Statistical↗
PubMedDate not supplied

[Determination of the total quantity of carbohydrates in dried yeast].

Different colourimetric methods for measuring carbohydrates in yeast have been compared. A method using 5% phenol aqueous solution in the presence of concentrated sulphuric acid has been developed to quantitate carbohydrates. The method has been described as applied to an analysis of dry yeast.

Candida↗
PubMed1984

Comparisons of the effects of vacuum-uv and far-uv synchrotron radiation on dry yeast cells of different uv sensitivities.

Far-uv-sensitive (rad l/rad l) and wild-type cells of diploid Saccharomyces cerevisiae were irradiated in vacuum at 155, 170, 220, and 250 nm using synchrotron radiation (SR). Inactivation, gene conversion at leu l, and membrane damage as judged by methylene blue penetration were measured. Radiations of all these wavelengths killed dry yeast cells. In the vacuum uv, radiation at 155 and 170 nm induced membrane damage but not gene conversion, whereas far-uv radiation at 220 and 250 nm induced gene conversion but not membrane damage. The far-uv-sensitive strain showed no enhanced sensitivity to vacuum-uv radiation. These results indicate that damage to the cell membrane is considerably more important than to nuclear DNA for yeast cell inactivation by vacuum-uv radiation.

Cell Survival↗
PubMedDate not supplied

Field-flow fractionation as analytical technique for the characterization of dry yeast: correlation with wine fermentation activity.

Important oenological properties of wine depend on the winemaking yeast used in the fermentation process. There is considerable controversy about the quality of yeast, and a simple and cheap analytical methodology for quality control of yeast is needed. Gravitational field flow fractionation (GFFF) was used to characterize several commercial active dry wine yeasts from Saccharomyces cerevisiae and Saccharomyces bayanus and to assess the quality of the raw material before use. Laboratory-scale fermentations were performed using two different S. cerevisiae strains as inocula, and GFFF was used to follow the behavior of yeast cells during alcoholic fermentation. The viable/nonviable cell ratio was obtained by flow cytometry (FC) using propidium iodide as fluorescent dye. In each experiment, the amount of dry wine yeast to be used was calculated in order to provide the same quantity of viable cells. Kinetic studies of the fermentation process were performed controlling the density of the must, from 1.071 to 0.989 (20/20 density), and the total residual sugars, from 170 to 3 g/L. During the wine fermentation process, differences in the peak profiles obtained by GFFF between the two types of commercial yeasts that can be related with the unlike cell growth were observed. Moreover, the strains showed different fermentation kinetic profiles that could be correlated with the corresponding fractograms monitored by GFFF. These results allow optimism that sedimentation FFF techniques could be successfully used for quality assessment of the raw material and to predict yeast behavior during yeast-based bioprocesses such as wine production.

Cell Culture Techniques↗