Lignin removal was in general very high (see Table 3). This
means that residual lignin contents in the solids that were hydrolyzed
and fermented were low. Therefore, observed results must
not be due to the form of this residual lignin. Results cannot be
either explained by the cellulose recovery because it was also very
high in all cases. The form of the cellulose remaining in the solid
could be an important parameter affecting the results. The pretreatment
method can modifies the structural properties of solid
by increasing the surface area and decreasing the crystallinity
and thus enhancing the hydrolysis efficiency [29,45–48]. Additionally,
in this work only cellulolytic enzymes were used, therefore,
they are not able to attack the hemicellulosic fraction. It has been
reported that hemicellulose provides the key barrier to cellulose
breakdown by enzymes [49]. Based on this, the content and form
of hemicellulose should also play an important role in the hydrolysis
of cellulose.