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Effect of Sorghum Decortication and Use of Protease Before Liquefaction with Thermoresistant α-Amylase on Efficiency of Bioethanol Production

¹Departamento de Biotecnología e Ingeniería de Alimentos, Centro de Biotecnología. Tecnológico de Monterrey, Av. Eugenio Garza Sada 2501 Sur, CP 64849, Monterrey, N.L. México. ²Corresponding author. Phone: 52-81-83284132. Fax: 52-81-83284136. E-mail: sserna@itesm.mx

The aim was to study the dual effect of sorghum decortication and protease treatment before liquefaction with α-amylase on the performance of subsequent steps of saccharification and fermentation. A bifactorial experiment with a level of confidence of P < 0.05 was designed to study differences among grains (maize, whole, and decorticated sorghum) and the effectiveness of the protease before liquefaction. Sorghum was decorticated to remove most of the pericarp and part of the germ and increase starch concentration of the feedstock. The decorticated sorghum had significantly higher starch hydrolysis during liquefaction compared with the whole kernel. These hydrolyzates contained ≈50% more reducing sugars than the untreated counterparts. At the end of saccharification, the final glucose concentration in hydrolyzates treated without protease was the highest for maize (180 mg/mL), followed by decorticated sorghum (165 mg/mL), and whole sorghum (145 mg/mL). Decortication and protease treatment had a significant effect on fermentation times. In decorticated sorghum mash treated with and without protease, fermentation times were 22 and 60 hr, respectively. The decorticated sorghum treated with protease yielded similar amounts of ethanol compared with maize and 44% more ethanol compared with the untreated whole sorghum. Both sorghum decortication and protease treatments before hydrolysis with α-amylase are recommended to increase ethanol yields, lower yields of distilled grains, and save liquefaction, saccharification, and fermentation times.