Preheating Followed by Simultaneous Viscosity Reduction, Hydrolysis, and Fermentation: Simplifying the Process of Ethanol Production from Sweet Potato

Abstract

In traditional methods, the ethanol production from starchy raw materials includes the stages of viscosity reduction, full hydrolysis, and fermentation, which are carried out in two or more steps. We propose to perform all these steps together with the method called P-SVHF (preheating followed by simultaneous viscosity reduction, hydrolysis, and fermentation). The sweet potato starch was hydrolyzed by applying a commercial enzyme mixture specially developed to degrade granular starch. Nevertheless, when starch was previously gelatinized, the ethanol production was 52% higher than that in which starch was in the granular form. Thus, the proposed method (P-SVHF) also includes the starch gelatinization stage (preheating). In the P-SVHF method, energy is saved through (i) reducing the mass that is heated (only sweet potatoes), and (ii) applying a temperature (76 °C) which is lower than what is usually used during the liquefaction (≥ 85 °C), then an energy saving of 48% in comparison with traditional methods was estimated. After the method definition, a central composite design was carried out to evaluate the influence of pH, temperature, and time in the SVHF. The significant contributions of the optimization were the time reduction, i.e., from 24 h to 18–19 h, and the ethanol conversion efficiency increased to about 93%.