Eduardo Ximenes, Laboratory of Renewable Resource Engineering (LORRE), Purdue University, Potter Engineering Center, 500 Central Dr., West Lafayette, IN 47906, Youngmi Kim, Laboratory of Renewable Resources Engineering (LORRE), Purdue University, Potter Engineering Center, 500 Central Drive, West Lafayette, IN 47907-2022, Nathan S. Mosier, Agricultural and Biological Engineering & Laboratory of Renewable Resources Engineering (LORRE), Purdue University, Potter Engineering Center, 500 Central Drive, West Lafayette, IN 47907-2022, and Michael R. Ladisch, Laboratory of Renewable Resources Engineering Department, Purdue University, Potter Engineering Center, 500 Central Drive, West Lafayette, IN 47907-2022.
Compounds that inhibit the enzymatic hydrolysis of cellulose to fermentable sugars may be present when lignocellulosic materials are pretreated. We have observed the reduction in extent of conversion of pretreated cellulose to fermentable sugars as the solids loading (concentration of solid biomass material) is increased even though the ratio of enzyme to solids material is kept constant. In addition, washing the pretreated cellulosic material results in greater extents of conversion. We have identified various potential inhibitors including ferulic acid and other phenolic compounds which may help to describe this phenomenon. Glucose yield reduction up to 70% for the hydrolysis of wet cake by commercial cellulase and ß-glucosidase in the presence of 0.5% (w/v) ferulic acid were observed in our studies. Comparing enzymes from different microorganism sources, we have also found that some are more resistant to inhibition by ferulic acid than others. This paper describes the chemistry and possible mechanisms for inhibition of industrial cellulase and hemicellulase enzymes by unknown components that are present in lignocellulosic material.