High‐Solids Bio‐Conversion of Maize Starch to Sugars and Ethanol

In current industrial production, maize is the predominant crop used to produce starch which is converted to sugars. In this study, liquefaction and fermentation of normal maize starch at different solid contents are examined. Starch is liquefied at solid contents from 20 to 60% by thermostable α‐amylase at 90 °C. The molecular weight distributions of the dextrins from starch liquefaction, determined by gel‐permeation chromatography, are practically the same for those generated at 20–40% solids, whereas those at 50–60% solids contain increased levels of high molecular weight dextrins. A higher solids level (40–60%) requires more α‐amylase to produce liquefied starch with a reducing sugar content of 9–15%. The starch hydrolysates are subjected to a simultaneous saccharification and fermentation (SSF) process that is conducted at 20–60% solids, 30 °C for up to 72 h. The highest ethanol concentration (17.4%, v/v) is obtained after 72 h from the 30% starch hydrolysate with reducing sugar content of 12–14%. Enzymatic liquefaction of normal maize starch at high solids content (40–60%) is feasible and the high solids enzyme conversion of starch could find potential applications in productions of sugars and chemicals made by fermentation of sugars.