7-70: Investigation of hemicellulase inhibition in high solids enzymatic hydrolysis

In recent years the biofuels research paradigm has shifted from ethanol to advanced biofuels that are readily integrated into the current transportation fuels infrastructure.  Many of the lignocellulosic bioconversion routes utilize xylose and/or glucose produced by operations such as pretreatment and enzymatic hydrolysis. The insoluble solids (IS) from pretreatment enter enzymatic hydrolysis and exist either in the presence of the solubilized pretreatment fraction (i.e. whole slurry) or absent of the solubilized fraction (i.e. washed).  Whole slurry enzymatic hydrolysis is preferred as it decreases water and utility use, but higher glucose and xylose yields have been observed utilizing washed solids.  Using commercially available hemicellulase and cellulase preparations we have observed no xylose production from high solids, whole slurry enzymatic hydrolysis, while greater than 80% xylan to xylose yields have been observed from high solids, washed IS enzymatic hydrolysis.  Previous work has shown end product inhibition of Aspergillus niger beta-D-xylosidase by D-xylose, and inhibition from phenolic acid compounds on the endoxylanase, XynA, from Clostridium cellulovorans.  In the present work a range of potential xylanase inhibitors observed in dilute-acid pretreatment slurries were dosed into washed IS or beechwood xylan at varied concentrations prior to enzymatic hydrolysis.  The pure component inhibitors studied include xylose, glucose, xylobiose, cellobiose, and phenolic acids.  Inhibition effects due to other solubilized components in dilute-acid pretreatment liquor (acetic acid, HMF, furfural) were studied by dosing pretreatment liquor at varied dilutions prior to enzymatic hydrolysis.  The concentration of inhibitor(s) that show an effect on xylose production during enzymatic hydrolysis is presented.