Title

Production of Bioethanol by Fermentation of Sugars Released by Dilute-acid and Enzymatic Hydrolysis of Soybean Meal

Date of Graduation

5-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor

Ruben O. Morawicki

Committee Member

Jean-Francois Meullenet

Second Committee Member

Ya-Jane Wang

Third Committee Member

Steven C. Ricke

Fourth Committee Member

Edward E. Gbur

Abstract

Soybean meal (SBM) is a co-product of soybean oil extraction mostly used as animal feed due to its protein content ranging from 40 to 49%. Additionally, SBM contains 35-42% of carbohydrates, half of which are structural, and the remaining consists of approximately 17% of mono- and disaccharides--especially sucrose--up to 8% oligosaccharides, and 1-2% starch. When used as animal feed, only sucrose and starch are digested and absorbed by monogastric animals. Although SBM contributes carbohydrates to their diet, its main function is to provide proteins. Therefore, the selective removal of carbohydrates would create a protein-enriched meal with a greater value, which would facilitate the formulation of diets, and a byproduct stream rich on fermentable sugars that could be used as a feedstock for fermentations. The aim of this research was to develop a process to treat SBM with a combination of treatments with dilute sulfuric acid at different concentrations, temperatures, and times followed by enzymatic hydrolysis with cellulase and ß-glucosidase after detoxification with activated carbon to reduce inhibitor effects. The final product was a high-protein SBM and a liquid fraction rich in fermentable sugars that was used in the production of ethanol via fermentation with Saccharomyces cerevisiae and Zymomonas mobilis. Treatments enhanced the crude protein content up to 58.6% d.b. with a lysine bioavailability up to 97%. An important balance among fermentable sugars (16.2% d.b. ), crude protein (55.5% d.b.) and color (close to untreated SBM) was reached with the treatment at 120°C, 1.5% H2SO4, and 30 min. S. cerevisiae yielded its maximum bioethanol production at 8 g/L and Z. mobilis 9.2 g/L without any supplementation of the fermentation broth

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