Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Ethanol production by corn wet-milling plants produces large quantities of the low-value, lignocellulosic co-product - corn fiber. A mixture of corn fiber combined with other by-products, including oil cake, steep liquor and stillage, is currently dried, pelletized and sold as corn gluten feed for dairy cattle. As wet-milling processes expand, additional uses of the fiber will be required to prevent an oversupply of animal feed. One approach for value-adding is to utilize corn fiber as a feedstock for production of more ethanol. Saccharification of the cellulose could liberate simple sugars for subsequent yeast fermentation to ethanol. Hydrolysis of corn fiber to simple sugars by the brown rot fungus, Gloeophyllum trabeum, was studied in this research using both suspended-culture and solid-state fermentations (SSF). Buffered anaerobic conditions (at 30ÃÂ°C) were created following SSF by G. trabeum to restrict the consumption of sugars by the fungus, and to enhance cellulose and hemicellulose saccharification by the fungal hydrolytic enzymes released during SSF. G. trabeum fermented some of the sugar to ethanol. The commercial yeast Saccharomyces cerevisiae was added during the anaerobic incubation step to enhance ethanol production from the fermentable sugars. The suspended-culture experiments were not effective for harvesting the sugars released from the corn fiber by fungal hydrolytic enzymes. Similar reducing sugar contents with and without G. trabeum inoculum, despite losses in the cultured fiber biomass, suggest that reducing sugars released by the extra cellular enzymes were consumed by the fungus. Whereas, SSF with G. trabeum for three days followed by buffered anaerobic incubation converted up to about 11 % (108 mg/g initial fiber) of the corn fiber into harvestable reducing sugars. With the addition of S. cerevisiae, sugars released by G. trabeum were fermented to a maximum yield to date of 4.0 g ethanol/100 g fiber. Finally, to my knowledge, this is the first reported observation of the fungus G. trabeum producing ethanol (up to 3.4 g/100 g fiber) under anaerobic or stressed conditions.
Mary Lynn Rasmussen
Rasmussen, Mary Lynn, "Sequential saccharification of corn fiber by the brown rot fungus, Gloeophyllum trabeum, and ethanol production by Saccharomyces cerevisiae" (2006). Retrospective Theses and Dissertations. 17763.