3-16: The comparative analysis of lignin from steam and organosolv pretreated substrates

During enzymatic hydrolysis, the lignin component of pretreated lignocellulosic substrates is known to decrease hydrolysis yields and influence the adsorption of cellulolytic enzymes. Although hydrophobic, electrostatic, and hydrogen bonding interactions between lignin and cellulases have been proposed as potential mechanisms for the effects of lignin on hydrolysis, there have been limited fundamental studies in this regard. In this study, steam and organosolv pretreated substrates from softwood (Lodgepole pine), hardwood (Poplar), and an agricultural residue (corn stover) were prepared with subsequent isolation of lignin via two methods. Lignin preparations isolated using protease treatment were compared to those obtained using dioxane extraction with respect to their chemical and physical properties and their effects on enzymatic hydrolysis. It was apparent that the lignin isolated using dioxane contained fewer carbohydrates and residual protein than those isolated using the protease method. The isolated lignin from lodgepole pine softwood seemed to be more inhibitory to enzymatic hydrolysis compared to lignin preparations isolated from corn stover and poplar. Further experiments were also conducted to determine the lignin-related factors that decrease the hydrolysis yields and influence protein content.