Optimization of bioethanol production during simultaneous saccharification and fermentation in very high-gravity cassava mash.

Hydrolysis and fermentation conditions for production of ethanol from very high-gravity cassava mash by Saccharomyces cerevisiae during simultaneous saccharification and fermentation (SSF) processing were optimized using a statistical methodology. During the first part of the study, Placket-Burman design (PBD) was used to study 19 factors that could potentially influence ethanol production. Gravity, particle size, initial pH, and fermentation temperature were identified as key factors that significantly increased final ethanol concentration. The main and interaction effects of these factors were subsequently evaluated based on a quadratic equation generated by central composite design (CCD) using response-surface methodology (RSM). Under the optimized very high-gravity conditions, the final ethanol concentration obtained from experiment increased from 8.21% (wt.%) to 15.03% (wt.%) and was in good agreement with model prediction. By employing two other commercial Saccharomyces strains, similar results were obtained under the same optimized condition. Therefore, we conclude that final ethanol concentration, ethanol productivity (V (P/max)), glucose utilization (Y (G/s), Y (P/s)), and fermentation efficiency (η (f)) were enhanced or maintained under the optimized condition of 40% gravity, 390 μm particle size, initial pH 5.5, and 27°C fermentation temperature.