Simultaneous Saccharification and Fermentation (SSF) of High Digestible Grain Sorghum for Ethanol Production

Abstract

The potential of high digestible grain sorghum (HDGS) with a modified starch protein endosperm matrix as an alternative to corn in ethanol production was investigated using simultaneous saccharification and fermentation (SSF). Protein and starch digestibilities and glucose and ethanol yields of HDGS were compared with those of normal grain sorghum (NGS) and corn using commercially available Saccharomyces cerevisiae yeast and the enzymes a-amylase and glucoamylase. Results showed that HDGS yielded higher amounts of glucose and ethanol than NGS and corn, particularly in the early part of the saccharification and fermentation process. After 2.5 h of saccharification, a glucose yield of 89% was obtained for HDGS compared to 72% and 75% for NGS and corn, respectively. An ethanol yield of 94% was obtained from HDGS compared to 81% and 84% for NGS and corn, respectively, after 21 to 24 h of fermentation. These results suggest that HDGS also has higher starch digestibility, resulting in a faster rate and higher enzymatic conversion of starch to glucose and higher yield of ethanol during hydrolysis and fermentation. When used in the current corn ethanol system, HDGS is expected to have several potential advantages, such as improved productivity of ethanol and quality of co-product animal feed (dry distillers dried grains with soluble, DDGS), reduced energy consumption during gelatinization and liquefaction, and reduced amount of enzyme during operation.