Sunday, May 4, 2008
3-17

Fermentation of pressurized batch hot water (PBHW) pretreated warm season grasses and inhibitor analysis for determination of value-added coproducts

Sarah K. Brandon1, William F. Anderson2, C. Kevin Chambliss3, Lekh Nath Sharma3, and Joy Doran-Peterson1. (1) Microbiology, University of Georgia, 204 Biological Sciences, Athens, GA 30602-2605, (2) Crop Breeding and Genetics Research Unit, USDA-ARS, P.O. Box 748, Tifton, GA 31793, (3) Chemistry and Biochemistry, Baylor University, One Bear Place #97348, Waco, TX 76798-7348

Warm-season grasses for livestock feeding are grown across a large portion of the southeastern United States, thus providing a rich and renewable source of biomass. We investigated Tifton 85 bermudagrass (Cynodon spp.), Merkeron napiergrass (Pennisetum purpureum), and GA 993 switchgrass (Panicum virgatum) as possible sources of biomass for conversion to ethanol using an engineered Escherichia coli strain. Grass samples were either left untreated or were pretreated using a pressurized batch hot water (PBHW) reactor.  Napiergrass consistently produced the lowest ethanol yield of the three grasses investigated. All three grasses had similar levels of p-coumaric and ferulic acid, known inhibitors of microbial metabolism, indicating that some other compound(s) may be responsible for the differences in fermentability observed.  To investigate this phenomenon further and to determine the content of additional phenolic-based value-added coproducts, fermentation samples were analyzed for 42 compounds after pretreatment, after enzymatic digestion, and after 144 hours of fermentation. Of the three grasses, Tifton 85 and GA 993 hold the most potential as possible bioenergy crops for ethanol production based on consistently higher ethanol yields than those obtained using napiergrass. Value-added coproduct removal prior to inoculation is being investigated and may increase ethanol yields further as some coproducts are inhibitory to bacterial growth and metabolism.

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