Avaliação preliminar da produção de etanol a partir de farinha de milho por levedura termotolerante

Abstract

The Brazilian industry of sugar-based energy has, over the last several years, experienced a surge in the diversity of its biomass sources with the rise of corn-based ethanol, most noticeably in the central-west region of the country. However, production of ethanol in Brazil is not without its challenges, as maintaining fermentation vats within an optimal temperature range proves to be particularly difficult when they carry out an exothermic reaction in a tropical climate prone to heat waves and strong summer seasons. The present study has been carried out with the purpose of assessing the viability of utilizing the thermotolerant yeast strain Saccharomyces cerevisiae LBGA-01 in the production of corn-based ethanol and potentially enabling an industrial-scale process which operates at a more doable temperature range. The experiment has been conducted at bench-scale, using corn flour with a starch content of 66% m.m-1 and started off with sequential hydrolysis and fermentation (SHF) processes at 36 and 38 °C and initial glucose concentrations of 100 and 200 g.L⁻¹. The conditions of assay SHF-200-38 were chosen for the following fermentations for its high efficiency value of 94.5%, and thus the reaction’s kinetics were mathematically modeled based on the Andrews-Levenspiel kinetic model. The saccharification step at 38 °C was modeled after the Michaelis-Menten model with product-driven inhibition, obtaining a residual standard deviation value of 4.13%. Based on the approximated parameters, a simulation of the simultaneous saccharification and fermentation (SSF) assay was performed, and the reaction was carried out at 38 °C with concentrations of glucose and starch equivalent to 183 g.L⁻¹ glucose. The SSF assay reached a final concentration of 92.29 g.L⁻¹ ethanol and efficiency of 94.62%, with a glucose depletion time of 34 h, shorter than the 36 h it took for depletion in the SHF assay and in literature-reported experiments. The mathematical modeling of the SSF assay revealed that the model that best represented the process was that of Levenspiel (no inhibition by substrate), pointing to there not being any significant amount of inhibition by glucose in the concentration range of the conducted SSF. The LBGA-01 strain proved to be capable of withstanding and thriving at such a high temperature as 38 °C, promising for an industrial process with simpler and cheaper heat-exchanging needs.