Understanding sugar yield loss and enzyme inhibition due to oligosaccharides accumulation during high solids-loading enzymatic hydrolisis.

Authors: XUE, SAISI - Michigan State University; UPPUGUNDLA, NIRMAL - Michigan State University; Bowman, Michael; JIN, MINJIE - Michigan State University; DA COSTA SOUSA, LEONARD - Michigan State University; CHUNDAWAT, SHISIR - Michigan State University; FOX, BRIAN - Michigan State University; CAVALIER, DAVID - Michigan State University; DALE, BRUCE - Michigan State University; BALAN, VENKATESH - Michigan State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/27/2015
Publication Date: 4/30/2015
Citation: Xue, S., Uppugundla, N., Bowman, M.J., Jin, M., da Costa Sousa, L., Chundawat, S.P.S., Fox, B., Cavalier, D., Dale, B.E., Balan, V. 2015. Understanding sugar yield loss and enzyme inhibition due to oligosaccharides accumulation during high solids-loading enzymatic hydrolysis [abstract]. Symposium on Biotechnology for Fuels and Chemicals.

Interpretive Summary:

Technical Abstract: During enzymatic hydrolysis of biomass, polysaccharides are cleaved by glycosyl hydrolases to soluble oligosaccharides and further hydrolyzed by ß-glucosidase, ß-xylosidase and other enzymes to monomeric sugars. However, not all oligosaccharides can be fully hydrolyzed and they may accumulate to 18-25% of the total soluble sugars at high solid loading (>3-25% solids loading). Oligosaccharide accumulation reduces ethanol yields because industrial ethanol-producing strains only consume monomeric sugars. Very little is understood about the nature of these oligomers and why they accumulate. In this work, we report a large-scale, robust method to separate and produce recalcitrant oligosaccharides using affinity-based charcoal fractionation and molecular weight-based gel filtration chromatography from high solids-loading AFEX-corn stover (ACS) hydrolysate. The low DP (degree of polymerization) oligosaccharides can be digested using commercial enzyme mixtures [Ctec2, Htec2 and Multifect pectinase(MP)] after being separated from the hydrolysate, while the high DP oligosaccharides were highly recalcitrant. Inhibition studies using pure substrates (Avicel and beechwood xylan) showed that low DP oligosaccharides are highly inhibitory to commercial enzymes, and the addition of monomeric sugars further intensified the inhibition. Chemical structures of oligosaccharides with varying DP, composition of monomeric sugars, and the extent of branching patterns have also been identified by acid hydrolysis, methylate derivatization, LC-MS and NMR. Using these oligosaccharides as substrates, enzymes and microbes arrays were screened to identify candidates to break down the un-hydrolyzed crosslinks and digest the oligosaccharides completely. This work helps us understand the mechanisms behind oligosaccharides accumulation and thus develop better strategies to increase sugar yields during biomass hydrolysis.