Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2006
Publication Date: 9/1/2006
Citation: Wang, P., Singh, V., Xue, H., Johnston, D., Rausch, K.D., Tumbleson, M.E. 2006. Comparison of raw starch hydrolyzing enzyme with conventional liquefaction and saccharification enzymes in dry-grind corn processing. Cereal Chemistry. 84(1):10-14. Interpretive Summary: The U. S. ethanol industry is growing rapidly and will become increasingly competitive as production levels reach the 7.5 billion gallon cap in the Renewable Fuel Standard. This necessitates the optimization of the overall process from a production and from an energy standpoint. The potential of using a reduced energy process for the conversion of starch to sugars by using new types of commercially available enzymes (native starch hydrolyzing enzymes) is of particular interest for energy reduction strategies. In order to evaluate the effectiveness of these new enzymes relative to the current process, a side-by-side comparison of the two processes was conducted using a laboratory scale procedure. The results show that the two processes produced similar yields of ethanol and coproducts. The native starch hydrolyzing enzymes are expected to significantly reduce the energy requirements for fuel ethanol production. These results will be useful to other ethanol researchers and producers and could help contribute to lowering the production cost of fuel ethanol benefiting farmers and fuel ethanol consumers.
Technical Abstract: In a conventional dry-grind corn process, starch is converted into dextrins using liquefaction enzymes at high temperatures (90–120 deg C) during a liquefaction step. Dextrins are hydrolyzed into sugars using saccharification enzymes during a simultaneous saccharification and fermentation (SSF) step. Recently, a raw starch hydrolyzing enzyme (RSH), Stargen 001, was developed that converts starch into dextrins at low temperatures (<48 deg C) and hydrolyzes dextrins into sugars during SSF. In this study, a dry-grind corn process using RSH enzyme was compared with two combinations (DG1 and DG2) of commercial liquefaction and saccharification enzymes. Dry-grind corn processes for all enzyme treatments were performed at the same process conditions except for the liquefaction step. For RSH and DG1 and DG2 treatments, ethanol concentrations at 72 hr of fermentation were 14.1–14.2% (v/v). All three enzyme treatments resulted in comparable ethanol conversion efficiencies, ethanol yields, and DDGS yields. Sugar profiles for the RSH treatment were different from DG1 and DG2 treatments, especially for glucose. During SSF, the highest glucose concentration for RSH treatment was 7% (w/v), whereas for DG1 and DG2 treatments, glucose concentrations had maximum of 19% (w/v). Glycerol concentrations were 0.5% (w/v) for RSH treatment and 0.8% (w/v) for DG1 and DG2 treatments.