Ethanol production by Zymomonas and Saccharomyces, advantages and disadvantages

Abstract

In order to evaluate the potential of Zymomonas mobilis and Saccharomyces cerevisiae for biotechnological ethanol production both microbes were grown aerobically and anaerobically at different glucose concentrations. The optimal values for ethanol production related to the theoretical values are 94% for Zymomonas and 88% for Saccharomyces, both under anaerobiosis. The corresponding figures for biomass are 2.5 g/l and 6.5 g/l and for total acid content 16 mM/l and 12 mM/l respectively: for other byproducts (such as aldehydes, ketones, esters) 330 mg/l and 280 mg/l respectively. For industrial fermentation Z.mobilis seems to be inferior to S.cerevisiae, because the advantage of higher ethanol and the lower biomass production of the bacterium is disadvantaged by the decrease in pH from 6.3 to 3.3 during yeast fermentation thus making sterilization of the medium unnecessary. The formation of acids and other byproducts may be neglected in practice, since in contrast to previous assumptions they are easy to separate during the rectification.