Modified simultaneous saccharification and fermentation for the production of bioethanol from highly concentrated raw corn starch

Bioethanol is one of the main bio-based molecules produced mainly from sugar cane, molasses and corn. Its environmental advantages allow it to be considered as safe and the cleanest fuel alternative. Starch is a wide-spread renewable carbohydrate conventionally used for bioethanol production via energy demanding liquefac-tion and saccharification processes. Raw starch hydrolysis using enzymes capable of degrading it below the gelatinization temperature significantly simplifies the process and reduces the cost of starch processing. In this study, an innovative modified simultaneous saccharification and fermentation process is proposed for the pro-duction of bioethanol from highly concentrated raw corn starch (30 % w/v). A two-step synergistic hydrolysis and fermentation was carried out in a single bioreactor vessel. To ensure high process efficiency, factors influ-encing the hydrolysis of concentrated raw corn starch by raw starch degrading alpha-amylase from Bacillus para-licheniformis ATCC 9945a (BliAmy) and commercial glucoamylase were investigated. Box-Behnken experimental design was used to predict the effects of different ratios of added enzymes, glucoamylase addition time, incu-bation time, and pH on hydrolysis yield. Optimal conditions for the highest yield of hydrolysis of raw corn starch (90 %) were obtained after 8 h using 5.0 IU BliAmy per mg of starch and 0.5 % (v/v) glucoamylase at pH 4.5 and 60 degrees C. Obtained glucose was further fermented with Saccharomyces cerevisiae at 30 degrees C in the same vessel for bioethanol production. Bioethanol concentration at 129.2 g/L, with productivity of 2.94 g/L/h and ethanol yield (YP/S) at 0.50 g EtOH/g total sugar, equivalent to 87.8 % theoretical yield, was obtained by modified simulta-neous saccharification and fermentation. This work enriches the information of bioethanol production and offers a novel strategy for raw starch hydrolysis under industrial conditions.