Simultaneous cold hydrolysis and fermentation of fresh sweet potato.

In recent decades, environmental and economic issues have pushed the production of biofuels worldwide. In this scenario, ethanol is the most produced biofuel. Starch is a potential substrate for this purpose, but the extra cost needed to hydrolyze it into glucose is still a drawback. As an alternative for the expensive and energy demanding conventional hydrolysis process, the cold hydrolysis is being studied. In this process, granular starch degrading enzymes act directly on raw starch granules; therefore, this hydrolysis is carried out below gelatinization temperature. As a consequence, the energy requirement can be significantly reduced. In this work, the cold hydrolysis and fermentation of fresh sweet potato were experimentally studied. For that, it was employed the sweet potato strain BRS Cuia, whose carbohydrate level reaches 28.7%. It can be translated into a potential to produce 185 L t−1 ethanol, or equivalently 7400 L ha−1. The enzymes blend adopted for the hydrolysis stage was Stargen™ 002. The surface response method indicated 200 g L−1 of sweet potato and 45 GAU g−1 of sweet potato as the best balance between high glucose formation rate and low enzyme consume. The 1 h pretreatment that achieved the highest glucose concentration was at 52 °C in the presence of the enzymes blend. Finally, the study of the simultaneous hydrolysis and fermentation showed that the medium supplementation has no significant effect over the fermentation performance, while the pH control is beneficial, improving the ethanol production in 54%.