Interpretive Summary: not required
Technical Abstract: Elephantgrass (Pennisetum purpureum) is a sub-tropical warm season grass that produces up to 40 Mg ha-1 dry matter in many portions of southern United States. Experiments have been conducted to determine the best protocols for conversion to ethanol and to use these methods to evaluate 30 genetically diverse accessions. Leaves and stems were fractionated dried, and milled, and processed separately for ethanol yield determinations. Fractionation isolates the affect of leaf to stem ratios, which is expected to vary with harvesting maturity. A novel aspect of the screening was that samples were extracted with water to remove soluble sugars, so, that plant cell walls were the sole source of carbohydrates. The milled samples were pretreated at 120°C for an hour with a dilute sulfuric acid catalyst (2% w/v). The whole hydrolysates were prepared for fermentation by neutralizing with calcium hydroxide, adding yeast nutrients, and commercial cellulases. The cultures were inoculated with a industrial Saccharomyces yeast strain and the simultaneous saccharificaton and fermentations cultured for 72 hours under microaerophilic conditions. Ethanol, residual glucose, and xylose yields were measured by HPLC analysis. Water extraction increased ethanol yields from leaves but decreased the yields from stems. Major differences in conversion efficiencies were found between leaves (124 – 187 mg ethanol/g non-soluble dry matter) and stems (48 – 130 mg ethanol/g non-soluble dry matter); mainly due to variations in digestible and indigestible fibers. A wide range of conversion efficiencies were also found among genetically distinct accessions of elephantgrass. Knowledge of these variations will provide valuable information to plant breeders for genetic improvements and for conversion facilities that choose elephantgrass as a dedicated biomass feedstock for bio-based fuels and products.