The experimental plan showed that soybean molasses
concentration of soluble solids of 200 g L-1 is better than the
concentations of 100 g L-1 and 300 g L-1, regarding to the
production of ethanol by Zymomonas mobilis. Also, the
kinetics tests showed the level 150 g L-1 is as good as 200 g L-1.
About the pH, it should be kept near neutrality (around 6.5).
Batch fermentation of soybean molasses by Zymomonas
mobilis in reactors provided higher ethanol productions and
productivity yields when compared to static fermentations (in
flasks). The results also showed that Zymomonas mobilis
NRRL 806 was superior to Saccharomyces cerevisiae in those
aspects. Although the net production of ethanol was similar at
the end of the process, the time required for the bacterium
was shorter, and the percentage of the theoretical maximum
yield was higher.
The bacteriumwas able to growin diluted soybeanmolasses
medium (150 g L-1 and 200 g L-1 of soluble solids) without
supplementation (neither additional nitrogen source, nor salts);
themicroorganismwas able to consume almost all the fructose
and glucose content, but was not able to uptake galactose. It
was also able to hydrolyze sucrose and stachyose, but this is not
true for soybean molasses trisaccharides, like raffinose.
These data encourage future works with enzymatic or acid
hydrolysis in order to increase the amounts of soybean
molasses fermentable sugars, as well as more accurate tests in
reactor in higher molasses concentrations and also encourages
further studies with this byproduct that can be in fact
used as a raw material and sometimes misfortunately classified
as a residue.