Hemicellulosic Ethanol Production by Immobilized Wild Brazilian Yeast Scheffersomyces shehatae UFMG-HM 52.2: Effects of Cell Concentration and Stirring Rate.

The use of sugarcane bagasse hemicellulosic hydrolysates presents an interesting alternative to second generation (2G) ethanol production. Techniques to enhance the fermentation process, e.g., the use of immobilized cells, is one of the key factors for efficient production. Here, the effect of two important parameters (cell concentration in immobilized system and stirring rate) on the 2G ethanol production using the wild Brazilian yeast S. shehatae UFMG-HM 52.2 immobilized in calcium alginate matrix are presented. A 2(2) full factorial design of experiments was carried out to evaluate the effect of cell concentrations in sodium alginate solution for immobilized bead production (3.0, 6.0, and 9.0 g/L) and stirring rate (150, 200, and 250 rpm) for 2G ethanol production. Statistical analysis showed that the use of both variables at low levels enhanced ethanol yield (YP/S). Under these process conditions, YP/S of 0.31 g/g and ethanol productivity (Qp) of 0.12 g/L h were achieved. Results showed the potential of this immobilized yeast in 2G ethanol production from C5 sugars and demonstrate the importance of adequate cell concentration in immobilized systems, a finding that stands to increase bioprocesses yields and productivity.