Tuesday, April 30, 2013
Exhibit Hall
Based on earlier studies in our laboratory on xylan/ xylooligomers solubilization and current understandings , it was hypothesized that hemicellulose (xylans) move out of the plant cell wall during thermochemical pretreatments into solution, and during pretreatment and/or upon cooling, precipitate onto biomass, especially under hydrothermal, low severity dilute sulfuric acid, and ammonia conditions. There it can form strong bonds with cellulose and/or lignin, which are different than natural linkages, resulting in less digestible cellulose. Thus, to investigate the effects of plausible hemicellulose (xylan) precipitation on cellulose conversion, hydrothermal, low severity dilute acid, and soaking in aqueous ammonia (SAA) pretreatments were performed on Avicel®PH 101 cellulose alone and mixed with commercial beechwood xylan and other pure hemicellulose compounds (guar gum galactomannan). Pretreated solids of Avicel mixed with hemicellulose were found to contain about 2 to 11% of precipitated, non-structural hemicellulose, and the these resulting solids showed a remarkably low digestibility (up to a 50% reduction) compared to the Avicel control. The precipitated hemicellulose was more inhibitory to cellulose conversion than structural hemicellulose present in holocellulose and α-cellulose. Furthermore, reductions in cellulose digestion were much higher than when hemicellulose or their oligomers were physically mixed with Avicel at similar or higher concentrations. Xylanase supplementation of cellulase, however, relieved the inhibition by precipitated xylan to a significant extent.