Evaluation of partial germ supplementation to improve dry fractionation ethanol fermentation
D. RAMCHANDRAN (1), P. Wang (2), B. Dien (3), W. Liu (1), M. A. Cotta (3), V. Singh (1). (1) University of Illinois, Urbana Champaign, Urbana, IL, U.S.A.; (2) National Energy Technology Laboratory, US Department of Energy, Pittsburgh, PA, U.S.A.; (3) National Center of Agricultural Utilization Research, USDA, Peoria, IL, U.S.A.
Ethanol fermentation of dry fractionated grits (corn endosperm pieces) containing different levels of germ was investigated using the dry grind process. Typically dry fractionated grits are prepared using a dry degerm defiber process, where germ and pericarp fiber are recovered as valuable co-products prior to fermentation of the endosperm (grit) fraction. Partial removal of germ fraction allows for marketing the germ fraction and potentially more efficient fermentation. Dry fractionated grits used in this study were obtained from a dry milling plant and a commercial dry grind facility. Dry milled endosperm grits were mixed with different amounts of germ (2, 5, 7 and 10% germ of the total sample) and compared to control grits (0% germ). Fermentation rates of germ supplemented grits (2, 5, 7 and 10% germ) were faster than control grits (0% germ). Addition of 2% germ was sufficient to achieve high ethanol concentration (19.1% v/v) compared to control grits (18.2% v/v). Commercial endosperm grits were prepared so as to recover 92, 95 and 97% of initial starch in the endosperm stream resulting in three grit samples: 92, 95 and 97% grits, respectively. Fermentation of 92, 95 and 97% grits were compared to ground whole corn (control) using conventional dry grind enzymes (comprising of alpha and gluco-amylases). Fermentation rates were slower and final ethanol concentrations were lower for commercial grits than control sample. However, in a final experiment, commercial grits were subjected to raw starch hydrolyzing enzyme (RSH) resulting in higher ethanol concentrations (20.2, 19.9, 19.5% v/v for 92, 95 and 97% grits, respectively) compared to whole corn control (18.6% v/v). Therefore, high ethanol concentrations can be achieved with dry fractionated grits provided inclusion of certain amount of germ and the use of RSH for controlled starch hydrolysis.
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