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Germination-Improved Ethanol Fermentation Performance of High-Tannin Sorghum in a Laboratory Dry-Grind Process¹

¹Contribution No. 09-009-J from the Kansas Agricultural Experiment Station, Manhattan, KS 66506. ²Department of Biological and Agricultural Engineering, Kansas State University, Manhattan, KS 66506. ³Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506. ⁴Corresponding author. Phone: 785-532-2919. Fax: 785-532-5825. E-mail address: dwang@ksu.edu

A high-tannin sorghum cultivar with 3.96% tannin content was used to study the effects of germination on its ethanol fermentation performance in a laboratory dry-grind process. High-tannin sorghum sample was germinated for 3 and 4 days. Original and germinated samples were analyzed for tannin, starch, protein, free amino nitrogen (FAN), and glucose content. Endosperm structures and flour pasting properties of germinated and nongerminated sorghum samples were examined using a scanning electron microscope (SEM) and rapid visco analyzer (RVA). Germination reduced tannin content from 3.96% to negligible levels. The free fermentable sugars (glucose, maltose, and maltotriose) in the germinated samples were significantly higher than those in the nongerminated control. Judged by the starch (starch plus dextrin) and free amino nitrogen contents in the mashed samples, germination improved degree of hydrolysis for starch by 13–20% and for protein by 5- to 10-fold during mashing. Germination significantly shortened the required fermentation time for ethanol production by 24–36 hr, increased ethanol fermentation efficiency by 2.6–4.0%, and reduced the residual starch content in the distillers dried grain with solubles (DDGS) compared to the nongerminated control. Ethanol yield for the 3-day germinated samples was 2.75 gallons/bushel, which was 3.1% higher than the 2.67 gallons for the nongerminated control. Ethanol yield for the 4-day germinated sorghum was 2.63 gallons/bushel due to excessive loss of starch during germination.