ARS | Publication request: Germ derived free amino nitrogen as supplement for corn endosperm fermentation

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2011
Publication Date: June 1, 2011
Citation: Vidal, B.C., Johnston, D., Rausch, K.D., Tumbleson, M.E., Singh, V. 2011. Germ derived free amino nitrogen as supplement for corn endosperm fermentation. Cereal Chemistry. 88(3)328-332.

Interpretive Summary: In an effort to improve the economics and efficiency of the corn to fuel ethanol industry, several plants have begun to use dry fractionation of the kernel prior to fermentation. This separation typically results in poor fermentation performance due to the removal of key nutrients required by the yeast. In an effort to overcome the performance issues, we investigated the use of a protease (an enzyme that converts protein into amino acids) to convert the available protein into a form that the yeast can utilize and compared this to supplementation with urea (a source of non-protein nitrogen). The addition of the protease was found to result in increased fermentation rates over urea supplementation. However, it did not increase the ethanol yields when compared to urea supplementation. The ethanol yields were found to be significantly greater than when there was no urea or protease supplementation. These results will be useful to other ethanol researchers and producers using or evaluating dry fractionation processes and could help lower the production cost of fuel ethanol benefiting farmers and fuel ethanol consumers.

Technical Abstract: Corn endosperm separated by dry fractionation could exhibit poor fermentation performance due to loss of germ components beneficial for yeast growth. Inorganic nitrogen and other nutritional supplementations are used to overcome sluggish fermentation. We investigated the use of a protease in generating free amino nitrogen (FAN) from germ as an alternative to exogenous nitrogen sources. Up to 300% more FAN can be generated from germ in 6 hr incubation with protease than without protease. Protease incubation also resulted in higher dry solid (ds) and total glucose contents in the germ hydrolyzates. During fermentation, ethanol yields were dependent on mash FAN concentrations. Ethanol yields increased to a maximum when FAN level was 80 to 90 mg FAN/100 g ds. At half the optimal FAN level (~40 mg FAN/100 g ds), nitrogen limitation occurred. However, germ FAN did not increase ethanol yields compared to urea supplementation, likely because germ FAN resulted in lower substrate consumption compared to urea supplementation. Lower substrate consumption correlated to the increase in residual maltose with increase in initial FAN. Ethanol production rates in 0 to 24 hr fermentation period were higher with germ FAN than with urea, thus decreasing overall fermentation time.