Tuesday, April 20, 2010
11-33

Effect of AFEX-pretreatment degradation products on fermentation by Saccharomyces cerevisiae 424A(LNH-ST)

Xiaoyu Tang1, Mingjie Jin2, Leonardo Sousa3, Dahai Gao3, Ramin Vismeh4, James F. Humpula3, Christa Gunawan5, Zeyi Xiao6, A. Daniel Jones7, Bruce E. Dale2, and Venkatesh Balan2. (1) Chemical Engineering and Materials Science, Biomass Conversion Research Lab (BCRL), Michigan State University, University Corporate Research Park, 3900 Collins Road, Lansing, MI 48910, (2) Deparment of Chemical Engineering and Materials Science, DOE Great Lakes Bioenergy Research Center, Michigan State University, 3900 Collins Road, Lansing, MI 48910, (3) Chemical Engineering and Materials Science, Michigan State University, Great Lakes Bioenergy Research Center (GLBRC), 3900 Collins Rd, Lansing, MI 48910, (4) Chemistry, Michigan State University, chemistry department, Michigan State University, East Lansing, MI 48824, (5) Biomass Conversion Research Laboratory, Department of Chemical Engineering and Materials Science, Michigan State University, 3700 Collins Rd, Lansing, MI 48910, (6) Chemical Engineering Machinery, Sichuan University, 24 South Section 1, Yihuan Road, Chengdu, 610065, China, (7) Department of Chemistry, Department of Biochemistry and Molecular Biology, Michigan State University, Room 209, Biochemistry Building, East Lansing, MI 48824

Several degradation products have been identified and quantified in AFEX pretreated corn stover using LC-MS and GC-MS techniques. They are broadly classified into four families: a) carboxylic acids, b) amides, c) furans and d) aldehydes. Some of these degradation products are known to be inhibitory to Saccharomyces cerevisiae 424A(LNH-ST) growth, particularly affecting xylose metabolism. Consequently, this fact will have detrimental effects on the economics of the process, by lowering the final ethanol yield and concentration. In this work, AFEX treated corn stover hydrolysate was separated in to several fractions based on their molecular weight using size exclusion chromatography. The effect of each fraction on fermentation of formulated pure sugar media was evaluated. Fractions which were found to cause major inhibitory effects on xylose consumption were identified and chemically characterized by mass spectrometry. The impact of the identified degradation products (at various concentrations) on glucose and xylose co-fermentation will be tested individually and in combinations. The aggregate and synergistic aspects of the inhibition and the impact of this inhibition on the kinetics of fermentation will be shown. With the help of this work we can identify several inhibitory compounds formed during AFEX pretreatment, that inhibit xylose fermentation. We believe that this information will be helpful for the molecular biologists to strengthen the xylose fermentation pathway.

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