(260e) Investigation of Hemicellulase Inhibition in the Production of Bioethanol

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).  The difference between washed IS and whole slurry enzymatic hydrolysis is the background concentration of sugars, organic acids, and other compounds prior to enzymatic hydrolysis.  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 little to no xylose production from high solids, whole slurry enzymatic hydrolysis on select dilute acid pretreatment slurries 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.  Organisms that utilize C-5 sugars in fermentation decrease the xylose concentration of the fermentation broth, which may allow for further xylose production during fermentation.  In the present work a range of potential xylanase inhibitors observed in dilute-acid pretreatment slurries and fermentation broths are dosed into washed IS and beechwood xylan at varied concentrations prior to enzymatic hydrolysis, and the effect on xylose production is presented.