Dried spent yeast (DSY) was used as a low-cost nitrogen supplement for
ethanol fermentation from sweet sorghum juice under very high gravity
(VHG) conditions by Saccharomyces cerevisiae NP 01. The fermentation
was carried out at 30\ubaC in a 5-litre bioreactor. The results
showed that DSY promoted ethanol production efficiencies. The ethanol
concentration (P), productivity (Qp) and yield (Yp/s) of the sterile
juice (total sugar of 280 g l-1) supplemented with 8 g l-1 of DSY were
not different from those supplemented with yeast extract and/or peptone
at the same amount. The initial yeast cell concentration of 5 x 107
cells ml-1 was found to be optimal for scale-up ethanol production. In
addition, an increase in sugar concentration in inoculum preparation
medium (from 10 to 100 g l-1) improved the ability of the inoculum to
produce ethanol under the VHG conditions. When S. cerevisiae NP 01
grown in the juice containing 100 g l-1 of total sugar was used as the
inoculum for ethanol fermentation, the P, Qp and Yp/s obtained were
108.98 \ub1 1.16 g l-1, 2.27 \ub1 0.06 g l-1 h-1 and 0.47 \ub1
0.01 g g-1, respectively. Similar results were also observed when the
ethanol fermentation was scaled up to a 50-litre bioreactor under the
same conditions. The cost of the sweet sorghum for ethanol production
was US$ 0.63 per litre of ethanol. These results clearly indicate the
high potential of using sweet sorghum juice supplemented with DSY under
VHG fermentation for ethanol production in industrial applications