Repeated ethanol production from sweet sorghum juice concentrated by membrane separation

Sequential batch fermentation from sweet sorghum juice concentrated by membrane separation (ultrafiltration permeation and nanofiltration concentration) to increase sugar contents, was investigated. Ethanol production at 5th batch fermentation by Saccharomyces cerevisiae BY4741 attained 113.7 ± 3.1 g L−1 (89.1 ± 2.2% of the theoretical ethanol yield) from 270.0 ± 22.6 g L−1 sugars, corresponding to 98.7% of ethanol titer attained at the 1st batch fermentation. This titer was comparable to ethanol production of 115.8 ± 0.6 g L−1 (87.1 ± 2.7% of the theoretical ethanol yield) obtained at 5th batch fermentation with 3 g L−1 yeast extract and 6 g L−1 polypeptone. Increase of cell density in the concentrated sweet sorghum juice was observed during sequential batch fermentation, as indicated by increased OD600. Utilization of sweet sorghum juice as the sole source, membrane separation, and S. cerevisiae was a cost-effective process for high ethanol production.