Date of Award

8-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Biosystems Engineering

Advisor

Drapcho, Caye M

Committee Member

Walker , Terry H

Committee Member

Nghiem , Nhuan P

Abstract

Corn fiber is a co-product of the corn wet-milling process that holds potential to become a value-added product. A process was developed to fractionate and isolate the hemicellulose B component of corn fiber generated by corn wet milling. The process consisted of pretreatment by soaking in aqueous ammonia (SAA) of starch-free corn fiber followed by enzymatic cellulose hydrolysis, during which the hemicellulose B was solubilized by cleavage into xylo-oligosaccharides. The hemicellulose A and B fractions were separated by adjustment of pH, and the hemicellulose B recovered by precipitation with ethanol.
The pretreatment step resulted in a high retention of major sugars, with 94% of initial glucan, 76% of initial xylan, and 78% of initial arabinan remaining in the pretreated material. Additionally, the pretreated material demonstrated a high glucan digestibility, with 85% of available glucan released as glucose after 72 hours of hydrolysis with cellulase. Xylan and arabinan digestibilities were low and very little xylan and arabinan remained in the solid phase after hydrolysis, indicating their cleavage to soluble xylo-oligosaccharides. A mass balance conducted around the process accounted for 87% of the initially present glucan, 91% of the initially present xylan, and 90% of the initially present arabinan.
The hemicellulose B was then hydrolyzed by a cocktail of enzymes that consisted of β-glucosidase, pectinase, xylanase, and ferulic acid esterase. Used by itself, the xylanase was very ineffective, demonstrating yields of less than 2% of xylose and arabinose. The greatest xylose and arabinose yields, 44% and 53%, respectively, were obtained by the combination of pectinase, used at 100 x manufacturer recommended dosage, and ferulic acid esterase, loaded at 10 x manufacturer recommended dosage. Addition of xylanase to this mixture had very little effect, increasing xylose yield by 0.03% while decreasing arabinose yield by 0.44%.
The glucose solutions resulting from the hydrolysis of the cellulose and starch fractions were then utilized in ethanol fermentation. They were combined in equal volumes and used instead of water to produce a corn mash, which was fermented for 70 hours. Compared to the fermentation of corn mashed with water, the use of the glucose solutions resulted in an increase of ethanol concentration in the beer of 2% (v/v). The overall fermentation efficiency was increased by 7% when the hydrolysis solutions were used in mashing.

Share

COinS