ARS | Publication request: Heterogeneous Biocatalyic Liquefaction and Saccharificaation of Starch for Ethanol

Submitted to: Corn Utilization Conference Proceedings
Publication Acceptance Date: July 22, 2004
Publication Date: September 19, 2004
Citation: Robertson, G.H., Wong, D., Lee, C.C., Wagschal, K.C. 2004. Heterogeneous Biocatalyic Liquefaction And Saccharificaation Of Starch For Ethanol. Corn Utilization Conference Proceedings, June 6-9, 2004, Indianapolis, Indiana, Abstract.

Technical Abstract: The biorefining of crop components 'starch, grain fiber, and crop residues ' to fermentable substrates for the production of high-value products such as ethanol, butanol, lactic acid, and citrate, always requires disassembly of natural or biopolymers to convertable substrates. Disassembly achieves solubility and ultimately simple sugars like glucose or xylose. This research seeks to reduce disassembly costs by using the emerging techniques of directed molecular evolution to develop new and efficient enzymes for these tasks. The need for improved efficiency in biopolymer disassembly is particularly relevant to the burgeoning U. S. ethanol industry which produces nearly 3 billion gallons of ethanol per year from corn or wheat grain. The starch from these grains is cooked at high temperature prior to enzymatic conversion, requiring 10-20% of the fuel value of the ethanol from fermentation. This energy could be saved by direct enzymatic hydrolysis of raw starch granules, with the elimination of the cooking step. Estimates for the energy savings are 8.8 to 19.6 percent of the fuel value of the ethanol. Scientists at the Western Regional Research Center are developing and evaluating highly efficient biocatalysis for this conversion. This is done by creating large numbers of enzyme variants of a parent molecule (barley alpha-amylase) and screening for best activity using conditions that would be applied at a full scale. The expectation is to find enzymes unlike those in nature that are tailored to process conditions. To date we have developed a set of amylases with raw-starch degrading properties that have more than 100 times the total activity of the parent amylases and 30 times the specific activity. Work is in progress to fully evaluate these as components of native starch digestion processes at laboratory and small pilot scale.