INDUSTRIALLY ROBUST ENZYMES AND MICROORGANISMS FOR PRODUCTION OF SUGARS AND ETHANOL FROM AGRICULTURAL BIOMASS
Location: National Center for Agricultural Utilization Research
Title: Energy crops for ethanol: a processing perspective
Submitted to: International Crop Science Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 18, 2008
Publication Date: May 1, 2008
Citation: Dien, B.S., Sarath, G., Pedersen, J.F., Vogel, K.P., Jung, H.G., Sattler, S.E., Casler, M.D., Mitchell, R., Cotta, M.A. 2008. Energy crops for ethanol: a processing perspective. In: Proceedings of the 5th International Crops Science Congress, April 13-18, 2008, Jeju Island, Korea. p. 1-5.
Global production of bioethanol for fuel is over 13 billions gal per year. Continued expansion of ethanol production will necessitate developing lignocellulose as an alternative to today’s use of starch and sugar producing crops. Dedicated energy crops are one such option. In the U.S., it has been estimated that enough perennial crops can be grown to supply 9–23 billion gal of ethanol/yr – assuming a yield of 60 gal/ton. However, further research is needed to understand the roles that agronomic practices and genetics play in affecting realizable ethanol yields. Biochemical conversion of biomass following thermo-chemical pretreatment is currently the leading technology for producing ethanol from these feedstocks. We compared a warm season grass (switchgrass), cool season grass (reed canary grass), and legume (alfalfa stems) for sugar production. To introduce further variation in this sample set, each species was harvested at 2 or 3 different maturities. Both species and maturity significantly affected carbohydrate content, composition, and sugar yields, indicating that looking beyond biomass yield may be important for determining feedstock suitability. We also evaluated the influence of plant genetics on ethanol yield. Over 100 samples of switchgrass were evaluated for ethanol yield by applying a low severity pretreatment assay. Xylose yields were positively correlated with xylan content as expected. However, ethanol yield could not be predicted by glucan content and was negatively correlated with acid detergent lignin content. More recently, a set of brown midrib lignin mutants of sorghum was likewise assayed for ethanol yield and, in this case, lignin composition was also found to negatively impact glucose yield. These results will be further discussed in the context of what can be done to further enhance the quality of energy crops for conversion to ethanol.