The influence of lignin migration and relocation during steam pretreatment on the enzymatic hydrolysis of softwood and corn stover biomass substrates

To be effective, steam pretreatment is typically carried out at temperatures/pressures above the glass transition point (Tg) of biomass lignin so that it can partly fluidize and relocate. The relocation of Douglas-fir and corn stover derived lignin was compared with the expectation that, with the corn stover lignin's lower hydrophobicity and molecular weight, it would be more readily fluidized. It was apparent that the Tg of lignin decreased as the moisture increased, with the easier access of steam to the corn stover lignin promoting its plasticization. Although the softwood lignin was more recalcitrant, when it was incorporated onto filter paper, it too could be plasticized, with its relocation enhancing enzymatic hydrolysis. When lignin recondensation was minimized, the increased hydrophobicity suppressed lignin relocation. It was apparent that differences in the accessibility of the lignin present in Douglas-fir and corn stover to steam significantly impacted lignin fluidization, relocation, and subsequent cellulose hydrolysis.