Effect of Liquid Hot Water Pretreatment on Enzyme Loading and Hydrolysis of Hardwood

A fundamental understanding of the combined factors that impact recalcitrance in enzyme hydrolysis of pretreated hardwood explains how cellulase loading may be decreased by a factor of 10 while maintaining 80% glucose yield when non-catalytic protein is added to the enzyme.  Factors that impact enzyme hydrolysis of solid biomass include the interaction of the cellulase and β-glucosidase components with solubilized phenolic inhibitors and the enhanced accessibility of lignin as a consequence of pretreatment.  While the added protein decreases overall specific activity of the enzyme, it also reduces cellulase adsorption on lignin, thus making more enzyme available for cellulose hydrolysis.  Consequently, 15 and 1.3 FPU cellulase/g total solids both give 80% yield, with the 1.3 FPU loading approaching the enzyme levels usually associated with amylases in starch hydrolysis.  These results reinvigorate motivation for the search for other approaches that prevent enzyme adsorption on lignin and enable high glucose yields at low enzyme loadings.  This paper presents measurements in our laboratory and prior reports from the literature to offer an explanation of how changes in the physical attributes of cellulosic biomass during liquid hot water pretreatment affect glucose yields and enzyme loading.