S. cerevisiae or
Z. mobilis, is superior in ethanol production from sugary/starchy
biomass. According to Karsch et al. [10], for industrial fermentation,
Z. mobilis seems to be inferior to S. cerevisiae, because the
advantage of the higher ethanol and the lower biomass production
of the bacterium is disadvantaged by the decrease in pH from 5.5
to 3.8 (as in the present study) during yeast fermentation thus
greatly impeding the occurrence of contaminants and making sterilization
of the medium not necessary; whereas, in case of Z. mobilis,
there might be a chance of contamination. Besides, during
ethanol fermentation, Z. mobilis encounters various environmental
stresses which adversely affect the ability of cells to perform efficiently
and consistently in converting sugars to ethanol. The major
stresses experienced by this microorganism are ethanol toxicity
and heat, which accumulate during metabolism of cells.