Statistical Approach for the Identification of Cellulolytic Enzyme Inhibitors Using Switchgrass Dilute Acid Prehydrolyzates as a Model System

The identification of biomass pretreatment generated compounds that impede cellulose hydrolysis is critical for improving the overall biomass saccharification process. The aim of this study was to correlate the identification and concentrations of switchgrass dilute acid pretreatment-generated compounds to cellulolytic enzyme inhibition and to tie this back to processing parameters. Preparation of 24 dilute acid prehydrolyzates was performed with switchgrass at temperatures from 140 to 180 degrees C, processing times from 10 to 40 min, and sulfuric acid concentrations of 0.5% or 1% (v/v). Results showed that all the switchgrass prehydrolyzates significantly reduced cellulolytic enzyme activities when assayed against model substrates. Exoglucanase was the most sensitive with its activity reduction, ranging from 58% to 88%; the inhibitory effect on beta-glucosidase and the cellulase cocktail ranged from 32% to 63% and 16% to 41%, respectively. Polyphenolic compounds were the most detrimental pretreatment-generated products to the cellulolytic enzymes, especially to exoglucanase. Limited enzyme inhibition, with acceptable biomass digestibility, was observed with pretreatment conditions corresponding to 160 degrees C. The statistically based approach used in this study proved to be a valid method to assess the effect of pretreatment-generated compounds on cellulolytic enzyme activities, linking their generation to pretreatment processing parameters.