Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/21/2006
Publication Date: 7/1/2007
Citation: Ximenes, E., Dien, B.S., Ladisch, M.R., Mosier, N., Cotta, M.A., Li, X. 2007. Enzyme production by industrially relevant fungi cultured on coproduct from corn dry grind ethanol plants. Applied Biochemistry and Biotechnology. 136-140:171-183. Interpretive Summary: Dried Distillers Grains with Solubles (DDGS) is the major and often only co-product for ethanol production using ground corn. For each bushel of corn fermented, 17 lb of DDGS is produced. As corn ethanol production has expanded, the selling price of DDGS has decreased because demand has not kept up with supply. In this work, DDGS is evaluated as a feedstock for enzyme production by commercial fungi. DDGS contains good amounts of protein and carbohydrates, two of the important ingredients required for growing fungi to produce enzymes. The results reported here show that the fungi grew well on DDGS and successfully produced enzymes. The enzyme titers were comparable to those reported for growing fungi on other complex feedstocks. Finally, the enzymes produced by the fungi were tested for their utility in extracting sugars from DDGS and found to be very effective.
Technical Abstract: Distillers Dried Grain with Solubles (DDGS) is the major co-product produced at a dry grind ethanol facility. Currently, it is sold primarily as a ruminant animal feed. DDGS is low cost and relatively high in protein and fiber contents. In this study, DDGS was investigated as carbon source for extracellular hydrolytic enzyme production. Two filamentous fungi, noted for their high cellulolytic and hemicellulolytic enzyme titers, were grown on DDGS: Trichoderma reesei Rut C-30 and Aspergillus niger NRRL 2001. DDGS was either used as delivered from the plant (untreated) or after being pretreated with hot-water. Both microorganisms secreted a broad range of enzymes when grown on DDGS. Higher xylanase titers were obtained when cultured on HW-DDGS compared to growth on untreated DDGS. Maximum xylanase titers were produced in 4 days for A. niger and 8 days for T. reesei in shake flask cultures. Larger amounts of enzymes were produced in bioreactors (5 L) either equipped with Rushton (for T. reesei) or updraft marine impellers (A. niger). Initial production titers were lower for bioreactor than for flask cultures, especially for T. reesei cultures. Improvement of enzyme titers were obtained using fed batch feeding schemes.