Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2009
Publication Date: 9/1/2010
Citation: Anderson, W.F., Dien, B.S., Jung, H.G., Vogel, K.P., Weimer, P.J. 2010. Effects of forage quality and cell wall constituents of bermudagrass on biochemical conversion to ethanol. BioEnergy Research. 3:225-237.
Interpretive Summary: Over 10 million acres of bermudagrass are grown for forage in Southern United States and is considered a potential feedstock for conversion of biomass to ethanol. There are differences in digestibility for livestock among bermudagrass cultivars and germplasm. This can be measured by a laboratory in vitro technique (IVDMD). This study was designed to determine the relationship between rumen digestibility estimates and ethanol production via simultaneous dilute acid hydrolysis and fermentation of free hexose sugars (SSF). The results from these analyses were also compared with results of another technique that measured in vitro gas production after 24 hours (NNG24) and 96 hours (NNG96), as well as dry matter composition. There was only a moderately high positive relationship between IVDMD and ethanol production. However, there was a high correlation between ethanol production and NNG24, indicating that this technique would be useful for evaluation of material for breeding purposes. NNG96 estimated IVDMD much better. Fiber as measured by neutral detergent fiber, and hemicellulose had much higher relationship with ethanol production and IVDMD than lignin content among these highly diverse bermudagrass lines.
Technical Abstract: Over 10 million acres of bermudagrass are grown for forage in Southern United States and is considered a potential feedstock for conversion of biomass to ethanol. Forage grasses have been improved through breeding to obtain high biomass yields and better forage quality (IVDMD). This improved biodegradability is conferred through lower lignin content and altered cell wall composition which may have a direct impact on their quality for use as a feedstock in biofuel production. Since enzymes present in bovine rumen are similar to enzymes used for conversion of cellulose to fermentable sugars, it has been proposed that highly digestible grasses would be amenable to enzymatic conversion to ethanol. However, it is not known how variation in rumen digestibility and fiber components correlates with efficiency of conversion to ethanol via fermentation. The objective of this paper was to determine relationships between ethanol production evaluated by simultaneous saccharification and fermentation (SSF), rumen digestibility (IVDMD), in vitro gas production (NNG24, NNG96), dry matter composition, and cell wall components for 50 genetically diverse bermudagrass accessions. Ethanol production was moderately correlated with IVDMD (R = 0.55) but highly correlated with NNG24 (R = 0.93). Regression models indicate that NDF and pentose sugars had highly significant effects on ethanol production. Variation among entries for IVDMD was similarly effected by variability of NDF and pentose sugars but also by nitrogen content within dry matter. Variation in lignin content only had minor contributions to ethanol production and IVDMD.