Fractionation of corn fiber treated by soaking in aqueous ammonia (SAA) for isolation of hemicellulose B and production of C5 sugars by enzyme hydrolysis

Authors: MONTANTI, JUSTIN MATTHEW - Clemson University; Nghiem, Nhuan; Johnston, David; DRAPCHO, CAYE - Clemson University

Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2011
Publication Date: 3/12/2011
Citation: Montanti, J., Nghiem, N.P., Johnston, D., Drapcho, C. 2011. Fractionation of corn fiber treated by soaking in aqueous ammonia (SAA) for isolation of hemicellulose B and production of C5 sugars by enzyme hydrolysis. Applied Biochemistry and Biotechnology. 164:1390-1404.

Interpretive Summary: Corn fiber is a co-product of the corn wet milling process, and is composed of the cellulosic components of the corn kernel, namely the pericarp and endosperm fiber. Recently, modifications to the dry grind process have been developed to allow pericarp fiber production there as well. While industrial yields of corn fiber vary, corn fiber production averages 11.5% of the mass of corn processed on a dry basis (db) in corn wet milling facilities. Wet milling corn fiber is of particular interest because of its high carbohydrate content and its currently low value. In addition, unlike many other agricultural residues, corn fiber is already available onsite in ethanol facilities. Thus, its utilization as a feedstock for other processes within the facility avoids the costs of gathering and transportation associated with other agricultural residues such as corn stover. Corn fiber is a lignocellulosic biomass, composed primarily of cellulose, hemicellulose, and lignin. Although the composition of corn fiber varies by source, cellulose and hemicellulose typically account for about 50% of the dry weight, with adherent starch comprising another 10 – 20%. Thus, corn fiber typically consists of about 70% recoverable sugars. A process was developed to fractionate corn fiber generated by corn wet milling to produce value-added products in a corn ethanol biorefinery. The process consisted of a pretreatment step followed by hydrolysis using commercial enzymes, during which the hemicellulose B (corn fiber gum) was solubilized and subsequently recovered by precipitation with ethanol. The recovered corn fiber gum could be sold as a stand-alone product or hydrolyzed by other commercial enzymes to release the fermentable sugar xylose, which could be converted biologically to high value-added co-products. The developed process offered a means for production of corn fiber gum as a value-added co-product and C5 sugars, which could be converted to other valuable co-products through fermentation in a corn wet-milling biorefinery.

Technical Abstract: 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) followed by enzymatic cellulose hydrolysis, during which the hemicellulose B was solubilized by cleavage into xylo-oligosaccharides and subsequently recovered by precipitation with ethanol. The pretreatment step resulted in high retention of major sugars and improvement of subsequent enzymatic hydrolysis. The recovered hemicellulose B was hydrolyzed by a cocktail of enzymes that consisted of Beta-glucosidase, pectinase, xylanase, and ferulic acid esterase (FAE). Xylanase alone was ineffective, demonstrating yields of less than 2 percent of xylose and arabinose. The greatest xylose and arabinose yields, 44 percent and 53 percent, respectively, were obtained by the combination of pectinase and FAE. A mass balance accounted for 87 percent of the initially present glucan, 91 percent of the xylan, and 90 percent of the arabinan. The developed process offered a means for production of corn fiber gum as a value-added co-product and C5 sugars, which could be converted to other valuable co-products through fermentation in a corn wet-milling biorefinery.