The assignment of specific substrate factors that render a substrate recalci­trant to cellulase hydrolysis is a controversial subject. Crystallinity, DP and specific surface area have all been thought to undergo significant changes during pretreatment, consequently influencing subsequent hydrolysis [2]. The original work prior to the 1990s, focusing on the physical character­ization of substrates, has been presented in previous reviews [2,7]. More recently, our group and others have published work correlating the physical properties of wood pulp fibers employed in papermaking to their hydrolyz — ability, as cellulases have been explored as a potential means to improve both the drainage of recycled pulps and to enhance pulp fiber properties [101]. Admittedly, pulps are not identical to substrates pretreated specifically for subsequent hydrolysis by cellulases. However, it should be noted that, sim­ilarly to pretreated substrates, pulp fibers also represent a lignocellulosic matrix and that the general principles gained from examining the physical properties of pulp fibers that affect hydrolysis can be cautiously extrapolated to substrates pretreated for bioconversion.

5.1