SSF has been considered an effective process for ethanol production
from lignocellulosic biomass, because it increases the yield
of ethanol by minimizing product inhibition, eliminating the need
to separate the saccharification and fermentation processes
(8,30,48). SSF has been shown to circumvent glucose inhibition of
the hydrolytic enzymes due to rapid assimilation of sugars by the
yeast used for fermentation (49).
The conversion of cellobiose to glucose has been identified as
the limiting step in cellulosic SSF by Tang et al. (23) based on studies
using a recombinant strain of S. cerevisiae that expresses the
b-glucosidase of Saccharomycopsis fibuligera. Tang et al. (23)
concluded that the ability of yeast strains to ferment cellobiose
could enhance the efficiency of cellulose hydrolysis. In our hands,
the use of S. cerevisiae INVSc1 expressing heterologous b-glucosidase
of A. aculeatus was as effective for ethanol production as the
addition of equivalent amounts of exogenous cellobiase Novozyme
188 when SSF was initiated.