Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2005
Publication Date: 9/9/2005
Citation: Wang, P., Singh, V., Xu, L., Johnston, D., Rausch, K.D., Tumbleson, M.E. 2005. Comparison of enzymatic (e-mill) and conventional dry-grind corn processes using a granular starch hydrolyzing enzyme. 2005. Cereal Chemistry.82(6):734-738.
Interpretive Summary: The production of ethanol using the current commercial process requires a significant amount of energy. The current ethanol process is still very efficient (net positive energy); further reductions in energy input could improve the overall economics of the process. Recently a commercial enzyme preparation that can hydrolyze (convert to sugars) starch without needing to cook (heat to make the starch more accessible to the conversion to sugars) was produced and if adopted by industry could significantly lower the energy requirements of ethanol production. Using this new enzyme together with a newly developed coproduct recovery procedure, may further improve the overall energy and economics of the process. To determine if this new type of enzyme could be used with this modified process, it was compared side-by-side with a procedure that used the new enzyme without coproduct recovery. The results were compared based on ethanol and coproduct yields. The data produced indicates that the new enzyme can be used in the modified process and has good product yields and economics. In fact the new enzymatic process produced 2.8 gallons of ethanol from a bushel of corn whereas only 2.6 gallons per bushel were produced by the old, conventional process. These results will benefit US corn growers, the US consumers and the US economy since improved domestic production of fuel can substitute for a material (oil) that must now be imported. These results will also benefit producers of fuel ethanol and enzyme companies wanting to improve production efficiencies.
Technical Abstract: A new low temperature liquefaction and saccharification enzyme STARGEN 001 (Genencor International, Palo Alto, CA) with high granular starch hydrolyzing activity was used in enzymatic dry-grind corn process to improve recovery of germ and pericarp fiber before fermentation. The enzymatic dry-grind corn process was compared with a conventional dry-grind corn process using STARGEN 001 with the same process parameters of dry solid content, pH, temperature, enzyme and yeast usage, and time. Sugar, ethanol, glycerol and organic acid profiles, fermentation rate, ethanol and coproducts yields were investigated. Final ethanol concentration of the enzymatic dry-grind corn process was 15.5 plus or minus 0.2% (v/v), which was 9.2% higher than the conventional process. Fermentation rate was also higher for enzymatic dry-grind corn process. Ethanol yields of enzymatic and conventional dry-grind corn processes were 0.395 plus or minus 0.006 and 0.417 plus or minus 0.002 L/kg (2.65 plus or minus 0.04 and 2.80 plus or minus 0.01 gal/bu), respectively. Three additional coproducts, germ 8.0 plus or minus 0.4% (db), pericarp fiber 7.7 plus or minus 0.4% (db), and endosperm fiber 5.2 plus or minus 0.6% (db) were produced in addition to DDGS with the enzymatic dry-grind corn process. DDGS generated from the enzymatic dry-grind corn process was 66% less than conventional process.