(512f) Effect of Enzyme-Mix On Saccharification of Switchgrass Pretreated by Soaking in Aqueous Ammonia

Authors: 
Pallapolu, V. R., Auburn University
Lee, Y. Y., Auburn University


Switchgrass is considered as one of the most promising bioenergy feedstocks because of high crop yield and wide adaptability to various climatic regions and soil conditions. Switchgrass pretreated by Soaking in Aqueous Ammonia (SAA) has the advantage of retaining high percentage of carbohydrates: all of glucan and 65-70% of xylan. Release of fermentable sugars from biomass is the rate-limiting and most costly step in the overall bioconversion process. The goal of this work is to seek proper enzyme mixtures that release six and five carbon sugars from SAA pretreated switchgrass with minimal protein loading during enzymatic hydrolysis. Feedstocks produced from SAA pretreatment were used in these experiments using various mix and combinations of commercial enzymes, which include Spezyme-CP, Novozyme-188, Multifect Xylanase, Multifect Pectinase, and β-Xylosidase. Pure cellulosic substrate of Avicel, chemical grade xylan and xylose were used as reference substrates. The measured reaction products were glucose, xylose, cellobiose, oligomers of glucose and xylose. Different CBU/FPU (Novozyme-188/Spezyme-CP) ratios were applied, and the corresponding glucan/xylan digestibilities were experimentally determined, to locate the optimum enzyme ratio. On increasing the total protein loading of cellulase and β-Glucosidase from 25 to 32 mg protein/g-glucan, only 4%/3% increase in glucan/xylan digestibility was observed, whereas by supplementation of same amount of xylanase and pectinase glucan/xylan digestibility increased by 12%/23% and 6%/16%, respectively. Supplementation of β-Glucosidase decreased the cellobiose and glucose and xylose oligomers, hence increased glucan/xylan digestibility. The data were further analyzed to understand the effect of β-Xylosidase on sugar release and glucose and xylose oligomers.