This thesis can be divided into two parts: one was to evaluate the effect of integrating coproducts of enzyme assisted aqueous extraction of oil from soybean oilseeds, namely soy skim and soy insoluble fiber, in corn fermentation when different yeast species are used, and the second was to evaluate the efficacy of different chemical preservatives in increasing the shelf life of distillers wet grains (DWG), which is a co-product of the corn fermentation process and sold as animal feed.

For evaluating the performance of different yeast species in ethanol production in an integrated corn-soy fermentation system, a review of published literature was conducted to understand the enzyme-assisted extraction process (EAEP) of oil from soybean. The review paper discusses in detail the evolution of enzymes based extraction process from aqueous extraction process and compares the process with conventional solvent-based oil extraction. The review indicates that the total time of oil extraction decreased and the oil yield from soybean oilseeds increased by 43-45% when enzymes were added to hexane-based oil extraction process. In aqueous extraction process, where water is used as extraction medium, the oil yield increased from 50% to around 85% when the soybean seeds were crushed using milling, flaking or extrusion. Hydrolytic enzymes were added to breakdown down cellulose and the protein network that captures oil molecules, which increased the oil yield to 98%. Pre-extraction steps such as flaking and extrusion, and enzymes used for extraction and de-emulsification (proteases and cellulases) are important factors that affect the oil and protein yield of EAEP of soybeans.

Once the process and factors related to EAEP was understood, co-fermentation of corn and soy products was carried out while testing the fermentation performance of two yeasts species (Pichia stipitis and Candida shehatae) and comparing it with Saccharomyces cerevisiae. Since S. cerevisiae cannot assimilate pentose sugars such as xylose into ethanol, P. stipitis and C. shehatae were added to the system. Baseline data were obtained in synthetic media with 100% glucose, 100% xylose and glucose-xylose mixture. Further, fermentation was carried out for 72 hours in slurry containing just ground corn and water and slurry with ground corn, liquid soy skim and soy insoluble fiber. The performance of the three yeast species was compared on the basis of ethanol yield, ethanol production rate, ethanol final concentration and by-product concentration. It was observed that there was no significant difference at p<0.05 between the ethanol yields of the yeasts species and their mixture in corn only slurry, the mixture of S. cerevisiae and C. shehatae had the highest ethanol yield when compared to others in corn-soy product slurry. Individually, the production rate of P. stipitis and C. shehatae was slightly lower but when inoculated along with S. cerevisiae, the maximum production rate was comparable to S. cerevisiae.

Distillers wet grains is a co-product of ethanol production process from corn fermentation. These are unfermented ground corn; rich in fat, protein and few minerals. Addition of DWG to animal feed at 8-10% inclusion rate increased the total feeding value from 100 to 178 according to Klopfenstein et al (2008). Distillers grains are either fed as a wet product or dried to 20-30% moisture content. While the shelf life of dry product is higher and it is easy to transport, wet product is cheaper since no drying cost is involved. Wet product is preferred by livestock producers with farm near an ethanol plant. Since the moisture content is as high as 60%, chemical preservatives are used to increase the shelf life. The aim of the third objective was to test the efficacy of four commercial chemical preservatives and to compare their performance with a new preservative under development. Lactic acid bacteria, yeast and mold and aerobic heterotrophic cells were enumerated on the day of addition of preservatives up to day 10. Mold-X and Fungiless were very effective in controlling the population of yeasts and mold over the period of ten days. The performance of the new product, SHIELD, increased with increasing concentration and it was observed that the preservative was the most effective in decreasing the population of aerobic heterotrophs.