The Effect of Types of Lignocellulosic Biomass on Autohydrolysis Liquor Inhibitor Composition

A liquor stream from autohydrolysis pretreatment of lignocellulosic biomass is enriched in dissolved hemicellulose and lignin-derived compounds, which have been demonstrated as inhibitory towards downstream enzymatic hydrolysis and fermentation.  A better understanding of its inhibitory potential is sought through compositional analysis of different liquors to identify water-soluble inhibitors and their respective concentrations.  Six different woody and non-woody feedstocks were hydrothermally treated at 180° C for 40 min to obtain liquors and the chemical composition was analyzed for carbohydrate content in the forms of oligomer and monomer, sugar degradation compounds (acetic acid, formic acid, furfural, 5-hydroxymethylfurfural), acid soluble and insoluble lignin, phenolic monomers, and ash. The inhibitory capability of lignin-derived phenolic monomers with respect to enzymatic hydrolysis was tested by comparison of total monomeric saccharide yields from enzymatic hydrolysis of bleached pulps enriched with pure phenolics and an inhibitor-free reference.  Per 100 g of wheat straw, autohydrolysis liquors were found to contain 15.93 g of carbohydrate monomers and oligomers, 2.46 g of sugar degradation compounds, 5.47 g of lignin, 2.33 g of ash, and a low quantity of a variety of phenolic monomers.  Enzymatic saccharification yields from bleached hardwood pulp decreased by 5.3% in the presence of high concentrations of the phenolic monomer vanillic acid.  Liquors from woody biomass contained a lower amount of monomeric and oligomeric carbohydrates, acid soluble and insoluble lignin, and ash.  Experimental work to identify and quantify phenolic monomers present in autohydrolysis liquor from different biomasses continues in effort to identify specific sources of inhibition to downstream saccharification and fermentation.