Effects of nitrogen source on ethanol production in very high gravity fermentation of corn starch

Nitrogen sources, the critical media component, were optimized to enhance ethanol production by Saccharomyces cerevisiae in very high gravity (VHG) fermentation of corn starch (340 g/l). Screening experiments revealed yeast extract as an ideal nitrogen source for ethanol production. When yeast extract concentration was controlled at 2%, ethanol yield and fermentation efficiency reached approximately 20.3% and 84.5%, respectively, after 72 h of fermentation. To reduce ethanol production cost, yeast extract supplementation was partially replaced with less expensive nitrogen sources, namely urea and ammonium sulfate. Combined effects of the three nitrogen sources on ethanol production were determined through central composite design. The optimum combination of nitrogen sources (0.6% yeast extract, 69 mM urea, and 26 mM ammonium sulfate) enabled ethanol yield and fermentation efficiency comparable to those supplemented with 2% yeast extract, indicating that urea and ammonium sulfate synergistically enhanced ethanol production by S. cerevisiae in VHG fermentation. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.