Calculation of fermentation parameters from the results of a batch test taking account of the volume of biomass in the fermenting medium
The values of fermentation parameters calculated from the measured concentrations of substrates and/or products may be significantly affected by the volume of biomass in the fermenting medium. Corrections proposed in this paper should be evaluated and, depending on their magnitude, considered in order to obtain more representative results.
Product inhibition during the feeding phasein fed-batch ethanol fermentation of sugar-cane blackstrap molasses
SummaryThe following equations represent the influence of the ethanol concentration (E) on the specific growth rate of the yeast cells (μ) and on the specific production rate of ethanol (ν) during the reactor filling phase in fed-batch fermentation of sugar-cane blackstrap molasses: μ = μ0 - k · E and v = v0 · K/(K +E)
On the intracellular accumulation of ethanol in yeast.
Ethanol produced in the course of a batch fermentation by Saccharomyces cerevisiae or added from the outside, affects adversely the specific rate of growth of the yeast population, its viability, its specific rate of fermentation, and the specific rates of the uptake of sugar and amino acids. The underlying mechanisms are many and include irreversible denaturation and hyperbolic noncompetitive inhibition of glycolytic enzymes, the exponential noncompetitive inhibition of glucose, maltose, and ammonium transport, the depression of the optimum and the maximum temperature for growth, the increase of the minimum temperature for growth, and the enhancement of thermal death and petite mutation. Nagodawithana and Steinkraus reported that added ethanol was less toxic for S. cerevisiae than ethanol produced by the yeast. The death rates were lower in the presence of added ethanol than those measured at similar external ethanol concentrations endogenously produced. They proposed that, due to an unbalance between the rates of production and the net outflux of ethanol, there would be an intracellular accumulation of ethanol which in turn would explain the apparently greater inhibitory potency of endogenously produced ethanol present in the medium. This hypothesis was supported by the findings of several authors who reported that the intracellularmore » concentration of ethanol, in the course of batch fermentation, is much higher than its concentration in the extracellular medium. The present work is an attempt to clarify this matter. (Refs. 32).« less