Use of bioluminometry for determination of active yeast biomass immobilized in ionotropic hydrogels.

The technique of bioluminometry was used to determine the biomass concentration of yeast cells immobilized in ionotropic hydrogel beads, including alginate, pectate, and kappa-carrageenan. The method uses determination of ATP extracted from viable cells, the concentration of which is then expressed as the active biomass concentration. Seven yeast strains divided into three categories (brewing, wine-making, and ethanol-producing yeasts) were tested, and different biomass concentrations were determined in all three immobilization materials. The described method is characterized by a good correlation (up to 99%) to classical dry biomass determination. The method is quicker, easier, and not so laborious, providing sufficient determination accuracy, and can be used for a rapid estimation of viable biomass in most biotechnological processes using immobilized living cells.

Changes in the yeast metabolism at very high-gravity wort fermentation.

The rate of ethanol production increased with increasing wort gravity up to the initial wort concentration of 24%, reaching the maximum ethanol concentration of 6.2%, but its attenuation reached only 49%. The intracellular trehalose accumulation was proportional to the initial wort gravity, at 24 or 30% wort fermentation increased 3 or 4.5 times, respectively, compared to 12% wort fermentation. Trehalose accumulation began after exhaustion of glucose, ceased after uptake of approximately 65% reducing saccharides, despite of increasing ethanol or remaining saccharide concentration in the environment.

Enhancement of yeast ethanol tolerance by calcium and magnesium.

Ethanol-induced changes of CO2 production were compared in three strains of Saccharomyces cerevisiae. CaCl2 and MgCl2 exerted protective effects against the action of ethanol. Optimal concentrations ensuring maximum of CO2 production at 10% (V/V) of ethanol under non-growing conditions were 3 mmol/L Ca2+ and 2 mmol/L Mg2+. Yeast growth with and without ethanol addition was stimulated by Mg2+ more than by Ca2+ during fermentation, whereas ethanol production was more efficient when both Ca2+ and Mg2+ were added.