Abstract
Distillers dried grain with solubles (DDGS) is the major coproduct 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 Asper gillus 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 hot water DDGS compared with growth on untreated DDGS. Maximum xylanase titers were produced in 4 d for A. niger and 8 d 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.
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