Abstract
An overview on the potential application of wheat milling by-products as substrate for fermentation in a small-scale bioreactor is presented. Model fermentations were conducted using glucose and dry baker's yeast. The overall ethanol yield was nearly stable (c.a. 0.35g/g), independent of mash glucose concentration. An overall ethanol productivity (Qv) of 3.48g/L⋅h was obtained using 100g-glucose/L as substrate. Slurries containing low-grade wheat flour (LG) (100, 200 or 300g/L) were used for simultaneous saccharification and fermentation (SSF) with Z. mobilis. The LG fermentation performance was evaluated based on the final ethanol concentration (P), Qv, ethanol yield (YP/S), ethanol production rate (Qp) and the glucose consumption rate (Qs). Mashes containing 200g-LG/L produced about 52g-ethanol/L, with an Qv of 2.17g/L⋅h. Based on the relatively high fermentation rate obtained from LG, reaching peak productivity after c.a. 9h of SSF, considerable savings on fermentation time was achieved, compared to industrial batch processes. In the year 2000 c.a. 0.34 million tons of LG were produced in Brazil; assuming that this by-product could be fully used as feedstock, the potential for producing bioethanol from LG would be 78.2 million L.
