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

Abstract

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 (rmax), limiting hydrolysis rate (rlim) at extended reaction time (24h), and substrate conversion, marking the transition between the rmax and rlim kinetic regimes (Ctrans). At apparent saturation of substrate (12.2g cellulose/L) with enzyme, rmax for pretreated wheat straw (∼9.6g/L/h) surpassed that for Avicel by about 1.7-fold whereas their rlim were almost identical (∼0.15g/L/h). Ctrans roughly doubled as enzyme/substrate loading was increased from 3.8 to 75FPU/g, suggesting Ctrans 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 rmax. Ctrans was higher for pretreated wheat straw (∼30%) than for Avicel (∼20%) under these conditions.