ARS | Publication request: Evaluation of waxy grain sorghum for ethanol production

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 24, 2011
Publication Date: November 1, 2011
Citation: Yan, S., Wu, X., Bean, S., Pedersen, J.F., Tesso, T., Chen, Y.R. and Wang, D. 2011. Evaluation of waxy grain sorghum for ethanol production. Cereal Chemistry. 88(6):589-595.

Interpretive Summary: Grain sorghum is one of starch-rich cereals that can be grown economically in the semi-arid regions of the world, unlike wheat, corn, and rice. Currently, feedstock for fuel ethanol production is about 95% corn grain and 4% sorghum grain which accounts for 35% total sorghum production in the United States. This means that sorghum could make a larger contribution to the nation’s fuel ethanol requirements. One of the aims for this study was to investigate whether ethanol yield and fermentation efficiency were influenced by the ratio of amylose and amylopectin of waxy grain sorghums. We found that the advantages of using waxy sorghums for ethanol production include less energy consumption during cooking process and shorter fermentation times. It was also found that the residue left after fermentation (DDGS) of waxy sorghums has higher protein but lower starch contents, which may have unique uses to the animal feed industry.

Technical Abstract: The objective of this research was to investigate the fermentation performance of waxy grain sorghum for ethanol production. Twenty-five waxy grain sorghum varieties were evaluated using a laboratory dry-grind procedure. Total starch and amylose contents were measured using colorimetric procedures. Total starch and amylose content ranged from 65.4 to 76.3% and 5.5 to 7.3%, respectively. Fermentation efficiencies were in the range of 86-93%, corresponding to ethanol yields of 2.61-3.03 gallons/bushel. The advantages of using waxy sorghums for ethanol production include less energy consumption during cooking process, higher starch and protein digestibility, higher free amino nitrogen content, and shorter fermentation times. The results showed a strong linear relationship between free amino nitrogen and fermentation rate. Fermentation rate increased as free amino nitrogen content increased, especially during the first 30 hours of fermentation (R2 = 0.90). Total starch content in distillers dried grains with solubles (DDGS) was less than 1% for all waxy varieties.