ARS | Publication request: Biochemical Conversion of Reduced Lignin Alfalfa Stems Into Ethanol

Submitted to: Biotechnology for Fuels and Chemicals Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 22, 2010
Publication Date: N/A

Technical Abstract: Alfalfa (Medicago sativa L.) has potential utility as an energy crop for conversion to biofuels because it is already produced commercially, grows as a perennial, and the protein enriched leaves can be marketed for animal feed. In this paper, the biomass processing characteristics of the stem material was evaluated for biochemical conversion into ethanol. To evaluate the potential of plant cell wall engineering to enhance product yields, a reduced lignin genotype was compared to its wild-type counterpart. Early and late cuttings were examined for chemical compositions. The samples had similar carbohydrate contents including a mean composition of 314 g glucan and 494 g total neutral carbohydrates per kg dry biomass, which corresponds to an average theoretical ethanol yield of 358 l/tone. Samples were pretreated with dilute-acid (1 hr, 121 deg C), neutralized, and fermented to ethanol by Saccharomyces cerevisiae D5A in the presence of commercial cellulases. Conversion efficiencies (as % theoretical yield, g/g) of glucans to ethanol were 52-66%. Mean ethanol yields were higher for the late vs. early cutting and the reduced vs. wild-type alfalfa samples. Finally, the biomass samples were treated at a higher temperature (180 deg C, 20 min) in the presence of dilute ammonium hydroxide, ammonia removed by evaporation, and the unwashed samples fermented using a xylose metabolizing variant of S. cerevisiae strain D5A. Cellulose and xylan were saccharified simultaneously with commercial cellulases and fermented. The ethanol conversion efficiencies were 58-70% within 72 hr based upon glucan and xylan contents.