COMPARISON OF AROMATIC MONOMERS IN LIGNOCELLULOSIC BIOMASS PREHYDROLYSATES

Differences in the relative toxicity of xylose-rich prehydrolysates de rived from woody and herbaceous feedstocks are likely due to the relat ive abundance of a variety of inhibitory compounds. Acetate, as well a s several aromatic monomers, has been shown to be an inhibitor of the xylose-fermenting yeast, Pichia stipitis. Comparative information on t he concentration of known and likely inhibitors, other than acetate, i s lacking. The present study provides data on the aromatic monomer com position of representative herbaceous and woody prehydrolysates. Dilut e-acid prehydrolysates were prepared from three feedstocks; two herbac eous, corn stover and switchgrass (Panicum virgatum L.), and one woody (poplar). The prehydrolysates were neutralized with Ca(OH)(2), extrac ted with ethyl acetate, trimethylsilylated, and analyzed by CC-MS. Fou rteen aromatic monomers were tentatively identified by comparison with published mass spectra. The concentrations of the aromatic monomers t otalled 112, 141 and 247 mg L-1 for corn stover, switchgrass and popla r prehydrolysates, respectively. This is also the order of increasing inhibition of growth and ethanol productivity observed for Pichia ferm entations. The woody prehydrolysate contained approximately four-fold more syringyl-based monomers than did the herbaceous prehydrolysates, while guaiacyl-containing compounds were more evenly distributed.