HPLC analyses of the liquid phases obtained after the NaOH
pretreatments showed the presence of acetic acid, formic acid
and furfural (in pretreatments at 120–133.6 C) which are
known to be formed in the degradation of hemicelluloses and
sugars. These compounds have a strong inhibiting effect on fermentation
with Saccharomyces cerevisiae, specially acetic acid
and furfural which decrease the specific velocity of growth of
microorganisms and, therefore, the volumetric ethanol yield
[42–44]. Therefore, the implementation of an additional step
of neutralization of pretreated materials in very important to
mitigate the effect of these inhibiting compounds and thus improve
the ethanol yield. Monomeric sugars, produced by hydrolysis
of cellulose and hemicelluloses, like glucose, xylose and
arabinose were also detected.