Sunday, April 29, 2007

Enzymatic hydrolysis of a variety of bermudagrass (Tifton 85) with improved biodegradability for ethanol production

Eduardo A. Ximenes1, Sarah K. Brandon2, and Joy Doran-Peterson2. (1) Agricultural Engineering, Purdue University, Potter Engineering Center, 500 Central Drive, West Lafayette, IN 47907-2022, (2) Microbiology, University of Georgia, 204 Biological Sciences, Athens, GA 30602-2605

In the ARS-USDA (Tifton, GA), an extensive breeding program has produced new varieties of bermudagrass (Cynadon dactylon) with improved biodegradability. One of those varieties (Tifton 85) has been evaluated in this work for potential use in ethanol production. Although cellulosic feedstocks are significantly less expensive than corn, the conversion to ethanol is more costly due to the extensive processing required. Previous studies in the literature have suggested that enzymatic hydrolysis, in addition to processing advantages, has great potential for cost reductions. In this study, we report ethanol production from bermudagrass as substrate (16.3 g/L), after a hot-water pretreatment (230ºC) and subsequent enzyme hydrolysis using a combination of commercial enzymes (cellulase and feruloyl esterase).  The reducing sugars liberated (412 mg/mL) during the enzymatic hydrolysis step were less than expected under the conditions used, probably due to inhibitory effects of the phenolic compounds on the cellulases and/or the need for a different enzyme mixture based more on the substrate characteristics. The later was first addressed here by growing Hyprocrea jecorina, an industrially relevant fungus, on untreated bermudagrass Tifton 85. Under these conditions, the fungus secretes a broad range of enzymes (cellulases, hemicellulase and auxiliary enzymes). Maximum xylanase activity (85 IU/mL) was found after 7 days of culturing. We also report here the comparative results for the use of our H. jecorina enzyme preparation in the enzyme hydrolysis step to those obtained by using commercial enzymes.