ARS | Publication request: Evaluating Herbaceous Perennials As Energy Crops for Production of Fuel Ethanol

Submitted to: Biotechnology for Fuels and Chemicals Symposium Proceedings
Publication Type: Abstract
Publication Acceptance Date: May 2, 2007
Publication Date: N/A

Technical Abstract: Herbaceous perennial forages have potential use as energy crops for producing ethanol. We have examined three species for which production systems exist: alfalfa, reed canarygrass, and switchgrass. These plant species represent a diverse set of physiologies and include a legume and warm and cool season grasses. Samples were collected at two or more maturity stages of each plant species. Alfalfa leaves have value as a protein feed and, therefore, only the stems were considered. The forage samples were analyzed for composition including soluble sugars, structural carbohydrates, Klason lignin, and ash. Total carbohydrates and lignin increased with maturity for the three plant species. The forage samples were pretreated using dilute-acid and the resulting hydrolysates evaluated for enzymatic digestibility and ethanol yield. Ethanol yield was determined by simultaneously saccharifying and fermenting the neutralized hydrolysates with Saccharomyces cerevisiae D5A. The alfalfa stems were found to require greater acid loading and a more severe pretreatment to obtain similar sugar yields compared to the other samples. However, for all three species, later maturity samples yielded less glucose than immature forages. Fermenting the hydrolysates was found to be problematic because of the presence of inhibitors. Specifically, it was found that fructose readily degraded to hydroxymethylfurfural during the pretreatment and appeared to stall the subsequent fermentation. This suggests that either soluble sugars will need to be extracted prior to treating with dilute-acid or alternate pretreatments will need to be considered.