Enzymatic hydrolysis of microcrystalline cellulose and pretreated wheat straw: A detailed comparison using convenient kinetic analysis

Marked slow-down of soluble sugar production at low degree of substrate conversion limits the space-time yield of enzymatic hydrolysis of ligno-cellulosic materials. A simple set of kinetic descriptors was developed to compare reducing sugar release from pure crystalline cellulose (Avicel) and pretreated wheat straw by Trichoderma reesei cellulase at 50°C. The focus was on the rate-retarding effect of maximum hydrolysis rate at reaction start (r_max), limiting hydrolysis rate (r_lim) at extended reaction time (24h), and substrate conversion, marking the transition between the r_max and r_lim kinetic regimes (C_trans). At apparent saturation of substrate (12.2g cellulose/L) with enzyme, r_max for pretreated wheat straw (~9.6g/L/h) surpassed that for Avicel by about 1.7-fold whereas their r_lim were almost identical (~0.15g/L/h). C_trans roughly doubled as enzyme/substrate loading was increased from 3.8 to 75FPU/g, suggesting C_trans to be a complex manifestation of cellulase-cellulose interaction, not an intrinsic substrate property. A low-temperature adsorption step preceding hydrolysis at 50°C resulted in enhanced cellulase binding at reaction start without increasing r_max. C_trans was higher for pretreated wheat straw (~30%) than for Avicel (~20%) under these conditions.