ARS | Publication request: Liquefaction, Saccharification, and Fermentation of Ammoniated Corn to ethanol

Submitted to: Biotechnology Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 25, 2008
Publication Date: November 24, 2008
Citation: Taylor, F., Kim, T., Abbas, C.A., Hicks, K.B. 2008. Liquefaction, Saccharification, and Fermentation of Ammoniated Corn to ethanol. Biotechnology Progress. 24:1267-1271.

Interpretive Summary: Ethanol is produced from corn in fermentors, where yeast cells consume the glucose sugar that comes from the starch in the corn. However, ethanol produced this way is too expensive to compete directly with gasoline. It has been suggested that the cost of producing fuel ethanol can be reduced by treating the whole corn kernels with anhydrous ammonia. Added ammonia provides nitrogen for yeast nutrition, and this pretreatment may help to separate and recover valuable co-products after grinding but before fermentation. Removing the non-fermentable components of the kernel will improve the fermentation process, and the sale of co-products will reduce the net cost of corn. This, in turn, may significantly reduce the overall cost of producing ethanol from corn. In this paper, the fermentability of ammoniated corn is compared to that of non-ammoniated corn in 3, 6, and 12-L fermentors and 50-mL shake flasks. Application of this technology may benefit ethanol producers, corn growers, transportation fuel consumers and taxpayers.

Technical Abstract: Treatment of whole corn kernels with anhydrous ammonia gas has been proposed as a way to facilitate the separation of non-fermentable coproducts before fermentation of the starch to ethanol, but the fermentability of ammoniated corn has not been thoroughly investigated. Also, it is intended that the added ammonia nitrogen in ammonia treated corn (~1 g per kg corn) may satisfy the yeast nutritional requirement for free amino nitrogen. In this study, several procedures for ammoniation, liquefaction, saccharification and fermentation at several scales (3-L, 6-L, 12-L and 50-mL) were used to determine the fermentation rate, final ethanol concentration, and ethanol yield from starch in ammoniated or non-ammoniated corn. It was found that the time to finish ammoniated corn fermentation was about eight hours longer than with non-ammoniated corn. The maximum achievable ethanol concentration at 50 h fermentation time was lower with ammoniated corn than with non-ammoniated corn. The extra nitrogen in ammoniated corn satisfied some of the yeast requirement for free amino nitrogen, thereby reducing the requirement for corn steep liquor. Based upon these results, ammoniation of corn does not appear to have a positive impact on the fermentability of corn to ethanol. Ammoniation may still be cost effective, if the advantages in terms of improved separations outweigh the disadvantages in terms of decreased fermentability.