Xylose was not detected in the hydrolysis of Avicel (Fig. 2B) but some was released from Celuflock due to its relatively high hemicellulose content. Interestingly, Avicel was a better substrate for the Penicillium enzymes than Celuflock , regardless of its high crystallinity index. Regarding pretreatment, water washing of steam-exploded materials was beneficial for enzymatic hydrolysis, revealing that even the small amount of water solubles (also referred to as C5 fraction) that is retained in the pretreated mate- rial after filtration contains adverse factors and/or inhibitory com- pounds that are enough to compromise the concerted action of Penicillium cellulases (Fig. 2A). By contrast, higher concentrations of xylose were detected in the enzymatic hydrolysates of unwashed substrates. This may be due to the retention of xylooligomers in the unwashed substrates that were not quantified in Table 3 because both primary and secondary water solubles derived from pretreatment were not subjected to a post-hydrolysis prior to HPLC analysis.