Monday, April 30, 2007 - 10:40 AM

Corn fiber: structure, composition, and response to enzymes for fermentable sugars and co-products

Danny E. Akin, Russell Research Center, Quality Assessment Research Unit, ARS-USDA, 950 College Station Road, Athens, GA 30605

Demands for ethanol require use of lignocellulosic sources and innovation to increase fermentation efficiencies. Corn fiber is a low-value residue that contains sugars and ferulic acid and could increase production efficiency.  Research was undertaken using enzymes to release sugars and ferulic acid from corn fiber.  Sections from intact corn kernels and corn fiber from commercial wet-milling sources were evaluated histochemically for type and location of aromatic compounds within cell walls. Milled corn fiber was incubated with commercial ferulic acid esterases and cellulases, and released phenolic acids and sugars were determined after various protocols.  Positive reactions with diazotized sulfanilic acid in the pericarp and aleurone layer suggested the presence of phenolic acids.  Treatment of corn fiber with alkali and assessment by gas chromatography indicated a prevalence of ferulic acid, most of which was ester-linked in the cell walls. Incubation with a commerical ferulic acid esterase mixture was effective in releasing ferulic acid and sugars (e.g., glucose, xylose) in the incubation medium.   Subsequent incubation with cellulase released more of these compounds.  Esterase + cellulase released significantly more fermentable sugars and ferulic acid than cellulase alone.  Various milling methods were tested to improve accessibility to enzymes and further increase the release of sugars and ferulic acids.  Ball milling changed the particle distribution based on standard sieves, significantly improved bioconversion of dry matter, and increased the enzymatic release of fermentable sugars and ferulic acid into the medium.  Esterases offer an opportunity to provide additional sugars as well as aromatic co-products from corn fiber.