Craig Long

Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology


Carbohydrates present in soybeans are generally undesirable due to their low digestibility and because they essentially "dilute" the concentration of more valuable components (protein and lipids). To remove these carbohydrates and thereby raise the titer of the more valuable components, ethanol production by yeast was investigated. Commercial cellulase enzymes (Novozyrne cellulase, glucosidase, and pectinase) were added to ground soybeans (SB), soybean meal (SBM), soybean hulls (SH), and soybean white flakes (WF) at a 10% solids loading rate to quantify hydrolyzed glucan in saccharification trials. These trials resulted in glucan reductions of 28%, 45%, 76%, and 80% in SBM, SB, SH, and WF respectively. Simultaneous saccharification and fermentation (SSF) trials were conducted at 5%, 10%, 15%, and 20% solids loading with Saccharomyces cerevisiae NRRL Y-2034 and Scheffersomyces stipitis NRRL Y-7124, with protein, fiber, and lipids analyzed at 10% solids trials for both saccharification and SSF. S. cerevisiae and S. stipitis produced ~3-12.5 g/L ethanol and ~2.5-8.6 g/L ethanol respectively on SB, SBM, and WF over these solid loading rates. Using SH as the feedstock resulted in higher ethanol titers for both S. cerevisiae (~9-23 g/L ethanol) and S. stipitis (~9.5-14.5 g/L). Protein concentrations decreased by 2.5-10% for the SB, SBM, and WF, but increased by 53%-55% in SH. Oil concentrations increased in all substrates; ~50% for SB, but by ~500-1300% for the other three. Soy molasses and soy solubles are byproducts of the conventional soy protein concentrate and soy protein isolate manufacturing processes, respectively. We examined conversion of the carbohydrates in these byproducts into ethanol. Standardized amounts of commercial cellulase enzymes (Novozyme cellulase, ~-glucosidase, and pectinase) were added to soy molasses and soy solubles solutions prepared at various solid loading rates (33%, 50%, 60%, 75%, and 80%) to hydrolyze oligosaccharides, followed by fermentation for 96 h using Saccharomyces cerevisiae NRRL Y-2034 and Scheffersomyces stipitis NRRL Y-7124. Ethanolextracted soybean meal (SBM) carbohydrates were also fermented for 96 h without enzymes. S. cerevisiae and S. stipitis produced ~12.5-45.0 g/L ethanol and ~6.0-28.0 g/L ethanol, respectively on molasses and solubles across these solid loading rates. The yeast produced ~6.5-17 g/L ethanol and ~6.5-22 g/L ethanol, respectively, on ethanol extracted carbohydrates.

Library of Congress Subject Headings

Soybean Biomass energy Ethanol



Number of Pages



South Dakota State University