Characterization of Amylose Lipid Complexes and Their Effect on the Dry Grind Ethanol Process

Amylose lipid complexes (AMLs) are likely to form during liquefaction of ground corn in the dry grind process. AML will form under high temperature (≥ 85 °C) and excess water conditions, due to interaction of gelatinized starch with corn lipids. AMLs are resistant to α-amylase action, resulting in a decrease in starch available for enzymatic hydrolysis. This affects sugar available for fermentation and the final ethanol yield. In this study, the effects of liquefaction temperature, corn particle size, slurry solids content, and different commercial α-amylases on AML formation are evaluated. AML content in post liquefaction solids (liquefact) is found to decrease from 3.46 to 1.00% as corn grind size is increased from 0.5 to 2.5 mm. Across all slurry solids contents tested (25, 32, and 34%), the mean difference in AML content for all three solids contents is 0.61% when liquefaction temperature is increased to 105 from 85 °C. At 85 °C, liquefact from all three α-amylases used, had similar AML content. However, when liquefaction temperature is increased to 105 °C, enzyme AA2 had lower AML production compared to other amylases. Overall, increasing liquefaction temperature to above 100 °C had the most predominant effect on reducing AML formation. Optimizing liquefaction parameters can help reduce AML formation and may improve profitability of the dry grind ethanol process.