Amino acid uptake by Saccharomyces cerevisiae during ethanol production

Authors: Johnston, David; Stoklosa, Ryan

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2023
Publication Date: 10/2/2023
Citation: Johnston, D., Stoklosa, R.J. 2023. Amino acid uptake by Saccharomyces cerevisiae during ethanol production. Cereal Chemistry. https://doi.org/10.1002/cche.10721.
DOI: https://doi.org/10.1002/cche.10721

Interpretive Summary: When corn is used for fuel ethanol production at high solids levels, the yeast used for producing the ethanol require sufficient nutrients to maintain good fermentation rates and reach high yields. Typically, urea is added as an inorganic nitrogen source so the yeast can produce the amino acids they need for proteins and ultimately the components needed for ethanol production. To better understand how yeast are impacted by nitrogen sources, we developed a solids free fermentation media made from corn and incorporated urea and/or a specific protease that was known to improve fermentation rates. The available amino acids in the media were followed during the fermentations and compared. The results showed that the protease increased the initial availability of certain amino acids and reached high ethanol yields without addition of urea. The urea addition allowed the yeast to produce significantly more amino acids during the fermentation process that were released into the media after all the available sugar was consumed. This information will benefit ethanol producers and researchers who are interested in optimization of ethanol production and conditions.

Technical Abstract: Fuel ethanol produced from corn requires proper yeast nutrients to maintain fermentation rates and to reach high yields. Corn used without supplementation provides an inadequate amount of nitrogen when fermentations are done at higher solids contents. Inorganic nitrogen in the form of urea or ammonia is typically used in commercial fuel ethanol production; however, organic nitrogen could also be used. To evaluate the impact of supplemental nitrogen and compare with the utilization of proteases, we developed a solids free media preparation to study and compare fermentations. Rates, yields, sugar utilization and amino acid concentrations were measured throughout the fermentations. Amino acid concentrations showed uptake occurred rapidly reaching 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 with supplemented media.