ARS | Publication request: Forage Energy Crops As Feedstocks for Production of Fuel Ethanol

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: December 8, 2006
Publication Date: December 8, 2006
Citation: Cotta, M.A., Dien, B.S., Iten, L.B., Jung, H.G., Lamb, J.F., Vogel, K.P., Mitchell, R., Sarath, G., Casler, M.D., Weimer, P.J. 2006. Forage energy crops as feedstocks for production of fuel ethanol [abstract]. Biocatalysis and Bioenergy. p. 21.

Technical Abstract: Alfalfa, reed canarygrass, and switchgrass are perennial herbaceous species that have potential as biomass energy crops in temperate regions. Each forage species was harvested at two or three maturity stages and analyzed for carbohydrates, lignin, protein, lipid, organic acids, and mineral composition. The biomass samples were pretreated with dilute sulfuric acid and subjected to enzymatic saccharification using a commercial cellulase preparation. Acid-released sugars and cellulase degradability of the biomass samples were determined. More mature biomass samples of all forage species contained less protein and mineral constituents than immature harvests. Alfalfa stems contained the most protein of the biomass samples, whereas reed canarygrass had more minerals and less lignin than the other biomass samples. Carbohydrate concentration overlapped among the biomass samples, but the two grasses contained more storage carbohydrates (starch and/or fructans) than the alfalfa stems. Cell wall polysaccharides of the grasses were richer in non-glucose residues than alfalfa stems, but cell wall glucose content of the biomass samples was similar. The alfalfa stem samples required a higher acid loading to achieve the same final pretreatment pH as the grasses. Increasing the temperature of dilute-acid pretreatment (150 deg C v 121 deg C) increased the yields of glucose of most all the forage samples; however, yield of non-glucose sugars was generally reduced at the higher pretreatment temperature. The loss in yield was due to the degradation of fructose (present in the biomass samples as free fructose, sucrose, and fructans). Efficiency of glucose release was negatively correlated with Klason lignin content of the biomass samples. Current results comparing ethanol yields following pretreatment with dilute acid and conversion by simultaneous saccharification and yeast fermentation will also be presented.