Influence of Calcium Ion on Ethanol Tolerance of Saccharomyces bayanus and Alcoholic Fermentation by Yeasts

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The addition of Ca2+ (as CaCl2) in optimal concentrations (0.75 to 2.0 mM) to a fermentation medium with a trace contaminating concentration of Ca2+ (0.025 mM) led to the rapid production of higher concentrations of ethanol by Saccharomyces cerevisiae, Saccharomyces bayanus, and Kluyveromyces marxianus. The positive effect of calcium supplementation (0.75 mM) on alcoholic fermentation by S. bayanus was explained by the increase in its ethanol tolerance. The ethanol inhibition of growth and fermentation followed the equation μxi = μoi [1 - (X/Xmi)]ni, where μoi and μxi are, respectively, the specific growth (i = g) and fermentation (i = f) rates in the absence or presence of a concentration (X) of added ethanol, and Xmi is the maximal concentration of ethanol which allows growth or fermentation. The toxic power is given by ni. In Ca2+ - supplemented medium (0.75 mM), ng = 0.42 for growth and nf = 0.43 for fermentation compared with 0.52 and 0.55, respectively, in unsupplemented medium; for both media, Xmg = 10% (vol/vol) and Xmf = 13% (vol/vol). For lethal concentrations of ethanol, the specific death rates were minimal for cells that were grown and incubated with ethanol in medium with an optimal concentration of Ca2+, maximal for cells grown and incubated with ethanol in unsupplemented medium, and intermediate for cells grown in unsupplemented medium and incubated with ethanol in calcium-supplemented medium. The effect of Ca2+ on the acidification curve of energized cells in the presence of ethanol was found to be closely associated with its protective effect on growth, fermentation, and viability.

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