To further support our interpretati

To further support our interpretation that the presaccharification
has a positive effect on ethanol production, we performed
SHF and SSF with and without presaccharification. Comparisons
of volumetric productivity (Qp) and ethanol yields of the variable
conditions are depicted in Fig. 5. The results show that the volumetric
productivity of fermentation and ethanol yields increase
with presaccharification time, from 0.43 g/L/h at 0 h to 1.79 g/L/h
after 72 h of presaccharification. The Qp of SSF with 72 h of presaccharification
was superior to the Qp of the SHF process with 72 h of
saccharification (Fig. 5). The volumetric productivity was calculated
using the minimum time required to reach the maximum
concentration of ethanol in the process. This occurred after 24 h
for SSF without presaccharification and after 8 h for the SHF and
SSF experiments with presaccharification. However, the total timeof the process was lower for SSF without presaccharification; 24 h
were required to reach the maximum concentration of ethanol
(10.31 g/L), whereas SSF after 72 h of presaccharification and 8 h
after fermentation yielded 14.36 g/L of ethanol.
This article provides incremental knowledge on alternative
ways for improving conversion technologies of cellulose into ethanol.
In particular, the utilization of thermotolerant yeast strains
during SSF allows the process to occur at higher temperatures that
are closer to the optimum temperature of cellulose hydrolysis
using commercial cellulases. The results obtained show that presaccharification
prior to fermentation, conducted in the same batch
allows for increased ethanol yields.