Amino acid uptake by Saccharomyces cerevisiae during ethanol production

Background and Objectives: Fuel ethanol produced from corn requires proper yeast nutrition. Corn without supplementation provides inadequate nitrogen at high solids levels. Inorganic nitrogen is typically added; however, organic nitrogen could also be added. To evaluate the impact of supplemental nitrogen and compare it with protease addition, we developed a solids-free corn media to study and compare fermentations.Findings: Amino acid concentrations showed uptake occurred rapidly as fermentation started and reached near zero levels for most amino acids. After sugar utilization was complete, amino acids were released by the yeast into the media. Protease addition without supplemental nitrogen reached rates and yields equivalent to supplemented media.Conclusions: Free amino acids decrease significantly at the beginning of fermentation but, under some conditions, are released again. Protease addition increased certain amino acids and reached equivalent ethanol yields without the addition of urea. Urea allowed the yeast to produce significantly more amino acids during fermentation that were released into the media after all the available sugar was consumed.Significance and Novelty: Amino acid uptake and release in corn fermentations has not been previously reported with this detail, and the improved understanding could lead to performance benefits.