Tuesday, May 1, 2012: 10:00 AM
Waterbury Ballroom, 2nd fl (Sheraton New Orleans)
This study characterizes the changes to lignin and polysaccharides in cell walls of grasses and dicots that were alkaline hydrogen peroxide (AHP) pretreated at varied severities or hydrothermally pretreated followed by AHP post-treatment. These bioenergy feedstocks represent relatively diverse cell wall phenotypes, including the monocots switchgrass (Panicum virgatum cv. Cave-In-Rock), corn stovers (a commercial hybrid and inbred brown midrib lines bm1 and bm3), and Miscanthus spp. and herbaceous and woody dicots including goldenrod (Solidago spp.) and hybrid poplar (Populus spp.). The residual cell walls are characterized in terms of total composition, p-hydroxycinnamic acid content for the grasses, syringyl/guaiacyl (S/G) ratio of the lignin, and the degree of condensation of the lignin. The results will show that for the grasses, the digestibility is correlated to total lignin content, p-hydroxycinnamic acid content, and xylan content, while S/G ratios do not appear to contribute to digestibility or delignification. The yield of uncondensed lignin as quantified by thioacidolysis GC/MS demonstrated a stark decrease after pretreatment indicating AHP pretreatment is particularly effective at cleaving β-O-4 bonds in grass lignins. The comparison of methods using NMR, thioacidolysis, and Py-GC/MS for estimating S/G ratios identified the challenge of distinguishing between “canonical” monolignols and p-hydroxycinnamic acids in grasses. In addition to the overall composition, the impact of AHP pretreatment on the polysaccharide fraction of the cell wall was characterized by high-throughput "glycome profiling" whereby an extensive library of plant glycan-directed monoclonal antibodies were screened against extractable polysaccharides.