Enzyme kinetic model for the formation of esters from alcohols by yeast

Abstract

Esters (acetates) were formed as by-products of alcoholic fermentation with Saccharomyces cerevisiae (brewer's top yeast) when the corresponding alcohols were added to the synthetic medium. The kinetics of ester formation from alcohols could be expressed by the Briggs-Haldane equation, modified to account for the presence of many competing substrates (alcohols). The maximum velocity was very susceptible to changes in the branching of the alcohols and to the position of the hydroxyl groups: primary alcohols were good substrates, but secondary and tertiary alcohols were poor substrates of ester formation. The results obtained at rather high concentrations of the alcohols could successfully be extrapolated to low concentrations as was verified by analyzing for the acetates of the branched pentanols in the unsupplemented medium; these alcohols are normally formed as by-products of alcoholic fermentation. When media containing several alcohols were fermented with various yeast species, the distribution between the various acetates was essentially the same, but the total level was quite different, indicating that the species differed with respect to the activity but not with respect to the specificity of the ester-forming enzyme system.