Optimization of the alcoholic concentration obtained from sugary cassava (Manihot esculenta Crantz) by response surface methodology.

Sugary cassava or mandiocaba is a cassava variety of potential use for bioethanol production. In this study, laboratory-scale fermentations were carried out in a bioreactor with a working volume of 1L, using the yeast strain LNF CAT-1. A central composite design (CCD) was applied to determine the extent to which pH, temperature, and yeast concentration influence ethanol production with the aim of improving the fermentation process. The individual effects and the interaction of these factors were analyzed using a surface response method. Physicochemical properties of the material were also investigated and the analysis of root characterization showed high moisture content (~91%) and a low amount of starch (~4.0%), ash values close to 1.0%, total fibers 0.4%, proteins 0.15%, and lipids 0.1%. The results obtained from the wort presented a low acidity (~0.2%), pH close to neutrality (~6.5%), total soluble solids values of ~5.8%, glucose content ~2.3%, fructose ~1.0%, and sucrose ~1.2%. The second-order polynomial regression model determined that the maximum ethanol production of 2.8% (v/v) would be obtained when the optimum pH, temperature, and yeast concentration were ~5.0, 32-36 ºC, and ~10-14 g L-1, respectively